Air compressor with inlet control mechanism and automatic inlet control mechanismAir Compressor Abstract Air Compressor Claims 1. An automatic inlet control mechanism for connection to a compression cylinder inlet of a reciprocating air compressor unit which produces compressed air at a predetermined rate of production through the use of a piston that reciprocates within a compression cylinder, said inlet control mechanism comprising: a mechanism body having a valve cavity, said valve cavity having a valve control chamber and a valve inlet chamber, a valve piston assembly positioned between said valve control chamber and said valve inlet chamber and constructed to prevent air flow between said valve control chamber and said valve inlet chamber; a valve inlet positioned to allow air to flow from the atmosphere surrounding the compressor unit and into said valve inlet chamber; a valve outlet having a valve outlet hole positioned to allow air to flow from said valve inlet chamber to the compression cylinder inlet, said valve outlet hole having a size sufficient to enable the compressor unit to produce compressed air at its predetermined rate of production; said valve piston assembly including a valve piston, said valve piston assembly being positioned to reciprocate within said valve cavity, a biasing member having a force which moves said valve piston assembly to a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet; a vent passageway allowing air to flow between said valve control chamber and the compression cylinder inlet; said vent passageway comprising at least one source of air to the compression cylinder inlet for a period of time after the compressor unit begins to draw air through the compression cylinder inlet, following the movement of said valve piston assembly to a position which prevents air from flowing from said valve inlet chamber through said valve outlet; said vent passageway including a vent orifice which restricts the flow of air from said valve control chamber to said compression cylinder inlet; and said vent orifice having an orifice size which allows air to be drawn, by the compressor unit, from said valve control chamber to the compression cylinder at a preselected rate which causes the compressor unit to produce compressed air at less than its predetermined rate of production, said valve control chamber having a volume which enables air to be drawn through said orifice from said valve control chamber by the compressor unit over a preselected time period until air within said valve control chamber is at a reduced pressure level which enables atmospheric pressure on said valve piston assembly from within said valve inlet chamber to overcome the force of said biasing member sufficiently to move said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to enable the compressor unit to produce compressed air at its predetermined rate of production. 2. The automatic inlet control mechanism of claim 1 wherein said valve piston assembly includes a diaphragm positioned between said valve control chamber and said valve inlet chamber, said diaphragm being constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said diaphragm being positioned to move toward said valve control chamber when air pressure within said valve inlet chamber is greater than air pressure within said valve control chamber, said diaphragm being positioned to move toward said valve inlet chamber when air pressure within said valve control chamber is greater than the air pressure within said valve inlet chamber. 3. The automatic inlet control mechanism of claim 1 wherein said vent passageway is included within said valve piston assembly, said vent orifice being located at a position in said valve piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to the compression cylinder inlet as said valve piston assembly reciprocates within said inlet control mechanism. 4. The automatic inlet control mechanism of claim 1 wherein said valve piston assembly includes a valve stem, said vent passageway being included within said valve piston assembly and extending through said valve stem, said vent orifice being located at a position in said valve piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to the compression cylinder inlet as said valve piston assembly reciprocates within said inlet control mechanism. 5. The automatic inlet control mechanism of claim 1 wherein said valve outlet includes a valve outlet hole having a tapered portion, said tapered portion having at least a first inner diameter and a second inner diameter, said first inner diameter of said tapered portion being larger than said second inner diameter and being located at a position that is closer to said valve inlet chamber than said second inner diameter when said mechanism is installed, said second inner diameter being sufficiently small to form an air restriction against said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet, said first inner diameter of said tapered portion being sufficiently large to allow air to pass between said tapered portion of said valve outlet and said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which allows air to flow from said valve inlet chamber through said valve outlet. 6. The automatic inlet control mechanism of claim 1 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet. 7. The automatic inlet control mechanism of claim 1 wherein said valve inlet includes a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 8. The automatic inlet control mechanism of claim 1 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet, said valve inlet including a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 9. The automatic inlet control mechanism of claim 1 wherein the compression cylinder inlet includes a cylinder inlet chamber for receiving air from the compression cylinder inlet before the air enters the compression cylinder, said vent passageway being positioned to allow for air to flow, outside said valve piston assembly, directly between said valve control chamber and the cylinder inlet chamber. 10. The automatic inlet control mechanism of claim 1 wherein: the compression cylinder inlet includes a cylinder inlet chamber for receiving air from the compression cylinder inlet before the air enters the compression cylinder, said vent passageway being positioned to allow for air to flow, outside said valve piston assembly, directly between said valve control chamber and the cylinder inlet chamber; and said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet. 11. The automatic inlet control mechanism of claim 1 wherein the compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from the compression cylinder inlet enters the compression cylinder, said automatic inlet control mechanism being located at least partially within the cylinder inlet chamber. 12. The automatic inlet control mechanism of claim 1 wherein: the compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from the compression cylinder inlet enters the compression cylinder, said automatic inlet control mechanism being located at least partially within the cylinder inlet chamber; and said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet. 13. An automatic inlet control mechanism for connection to a compression cylinder inlet of a reciprocating air compressor unit which produces compressed air at a predetermined rate of production through the use of a piston that reciprocates within a compression cylinder, said inlet control mechanism comprising: a mechanism body having a valve cavity, said valve cavity having a valve control chamber and a valve inlet chamber, a valve piston assembly positioned between said valve control chamber and said valve inlet chamber and constmcted to prevent air flow between said valve control chamber and said valve inlet chamber; a valve inlet positioned to allow air to flow from the atmosphere surrounding the compressor unit and into said valve inlet chamber; a valve outlet having a valve outlet hole positioned to allow air to flow from said valve inlet chamber to the compression cylinder inlet, said valve outlet hole having a size sufficient to enable the compressor unit to produce compressed air at its predetermined rate of production; said valve piston assembly including a valve piston, said valve piston assembly being positioned to reciprocate within said valve cavity, a biasing member having a force which moves said valve piston assembly to a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet; a vent passageway allowing air to flow between said valve control chamber and the compression cylinder inlet; said vent passageway comprising the primary source of air to the compression cylinder inlet for the period of time after the compressor unit begins to draw air through the compression cylinder inlet following the movement of said valve piston assembly to the position which prevents air from flowing from said valve inlet chamber through said valve outlet; said vent passageway including a vent orifice which restricts the flow of air from said valve control chamber to said compression cylinder inlet; and said vent orifice having an orifice size which allows air to be drawn, by the compressor unit, from said valve control chamber to the compression cylinder at a preselected rate which causes the compressor unit to produce compressed air at less than its predetermined rate of production, said valve control chamber having a volume which enables air to be drawn through said orifice from said valve control chamber by the compressor unit over a preselected time period until air within said valve control chamber is at a reduced pressure level which enables atmospheric pressure on said valve piston assembly from within said valve inlet chamber to overcome the force of said biasing member sufficiently to move said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compressor chamber inlet to enable the compressor unit to produce compressed air at its predetermined rate of production. 14. The automatic inlet control mechanism of claim 13 wherein said valve piston assembly includes a diaphragm positioned between said valve control chamber and said valve inlet chamber, said diaphragm being constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said diaphragm being positioned to move toward said valve control chamber when air pressure within said valve inlet chamber is greater than air pressure within said valve control chamber, said diaphragm being positioned to move toward said valve inlet chamber when air pressure within said valve control chamber is greater than the air pressure within said valve inlet chamber. 15. The automatic inlet control mechanism of claim 13 wherein said vent passageway is included within said valve piston assembly, said vent orifice being located at a position in said valve piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to the compression cylinder inlet as said valve piston assembly reciprocates within said inlet control mechanism. 16. The automatic inlet control mechanism of claim 13 wherein said valve piston assembly includes a valve stem, said vent passageway being included within said valve piston assembly and extending though said valve stem, said vent orifice being located at a position in said valve piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to the compression cylinder inlet as said valve piston assembly reciprocates within said inlet control mechanism. 17. The automatic inlet control mechanism of claim 13 wherein said valve outlet includes a valve outlet hole having a tapered portion, said tapered portion having at least a first inner diameter and a second inner diameter, said first inner diameter of said tapered portion being larger than said second inner diameter and being located at a position that is closer to said valve inlet chamber than said second inner diameter when said mechanism is installed, said second inner diameter being sufficiently small to form an air restriction against said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber though said valve outlet, said first inner diameter of said tapered portion being sufficiently large to allow air to pass between said tapered portion of said valve outlet and said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which allows air to flow from said valve inlet chamber through said valve outlet. 18. The automatic inlet control mechanism of claim 13 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber though said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet. 19. The automatic inlet control mechanism of claim 13 wherein said valve inlet includes a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 20. The automatic inlet control mechanism of claim 13 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet, said valve inlet including a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 21. The automatic inlet control mechanism of claim 13 wherein the compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from the compression cylinder inlet enters the compression cylinder, said automatic inlet control mechanism being located at least partially within the cylinder inlet chamber. 22. The automatic inlet control mechanism of claim 13 wherein: the compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from the compression cylinder inlet enters the compression cylinder, said automatic inlet control mechanism being located at least partially within the cylinder inlet chamber; and said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet. 23. An automatic inlet control mechanism for connection to a compression cylinder inlet of a reciprocating air compressor unit which produces compressed air at a predetermined rate of production through the use of a piston that reciprocates within a compression cylinder, said inlet control mechanism comprising: a mechanism body having a valve cavity, said valve cavity having a valve control chamber and a valve inlet chamber, a valve piston assembly positioned between said valve control chamber and said valve inlet chamber and constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said valve piston assembly including a diaphragm positioned between said valve control chamber and said valve inlet chamber, said diaphragm being constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said diaphragm being positioned to move toward said valve control chamber when air pressure within said valve inlet chamber is greater than air pressure within said valve control chamber, said diaphragm being positioned to move toward said valve inlet chamber when air pressure within said valve control chamber is greater than the air pressure within said valve inlet chamber; a valve inlet positioned to allow air to flow from the atmosphere surrounding the compressor unit and into said valve inlet chamber; a valve outlet having a valve outlet hole positioned to allow air to flow from said valve inlet chamber to the compression cylinder inlet, said valve outlet hole having a size sufficient to enable the compressor unit to produce compressed air at its predetermined rate of production; a valve piston and a valve stem included in said valve piston assembly, said valve piston assembly being positioned to reciprocate within said valve cavity, a biasing member having a force which moves said valve piston assembly to a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet; a vent passageway included in said valve piston assembly, said vent passageway allowing air to flow between said valve control chamber and the compression cylinder inlet; said vent passageway comprising at least one source of air to the compression cylinder inlet for a period of time after the compressor unit begins to draw air through the compression cylinder inlet, following the movement of said valve piston assembly to a position which prevents air from flowing from said valve inlet chamber through said valve outlet to the compression cylinder inlet; a valve outlet hole having a tapered portion included in said valve outlet, said tapered portion having a first inner diameter and a second inner diameter, said first inner diameter of said tapered portion being larger than said second inner diameter and being located at a position that is closer to said valve inlet chamber than said second inner diameter when said inlet control mechanism is installed, said second inner diameter being sufficiently small to form an air restriction against said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet, said first inner diameter of said tapered portion being sufficiently large to allow air to pass between said tapered portion of said valve outlet hole and said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which allows air to flow from said valve inlet chamber through said valve outlet; said vent passageway including a vent orifice which restricts the flow of air from said valve control chamber to said compression cylinder inlet; and said vent orifice having an orifice size which allows air to be drawn by the compressor unit from said valve control chamber to the compression cylinder at a preselected rate which causes the compressor unit to produce compressed air at less than its predetennined rate of production, said valve control chamber having a volume which enables air to be drawn through said orifice from said valve control chamber by the compressor unit over a preselected time period until air within said valve control chamber is at a reduced pressure level which enables atmospheric pressure on the valve piston assembly from within the valve inlet chamber to overcome the force of said biasing member sufficiently to move said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber through said valve outlet to enable the compressor unit to produce compressed air at its predetermined rate of production. 24. The automatic inlet control mechanism of claim 23 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet. 25. The automatic inlet control mechanism of claim 23 wherein said valve inlet includes a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 26. The automatic inlet control mechanism of claim 23 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet, said valve inlet including a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 27. An automatic inlet control mechanism for connection to a compression cylinder inlet of a reciprocating air compressor unit which produces compressed air at a predetermined rate of production through the use of a piston that reciprocates within a compression cylinder, said inlet control mechanism comprising: a mechanism body having a valve cavity, said valve cavity having a valve control chamber and a valve inlet chamber, a valve piston assembly positioned between said valve control chamber and said valve inlet chamber and constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said valve piston assembly including a diaphragm positioned between said valve control chamber and said valve inlet chamber, said diaphragm being constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said diaphragm being positioned to move toward said valve control chamber when air pressure within said valve inlet chamber is greater than air pressure within said valve control chamber, said diaphragm being positioned to move toward said valve inlet chamber when air pressure within said valve control chamber is greater than the air pressure within said valve inlet chamber; a valve inlet positioned to allow air to flow from the atmosphere surrounding the compressor unit and into said valve inlet chamber; a valve outlet having a valve outlet hole positioned to allow air to flow from said valve inlet chamber to the compression cylinder inlet, said valve outlet hole having a size sufficient to enable the compressor unit to produce compressed air at its predetermined rate of production; a valve piston and a valve stem included in said valve piston assembly, said valve piston assembly being positioned to reciprocate within said valve cavity, a biasing member having a force which moves said valve piston assembly to a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet; a vent passageway included in said valve piston assembly, said vent passageway allowing air to flow between said valve control chamber and the compression cylinder inlet; said vent passageway comprising the primary source of air to the compression cylinder inlet for a period of time after the compressor unit begins to draw air through the compression cylinder inlet, following the movement of said valve piston assembly to a position which prevents air from flowing from said valve inlet chamber through said valve outlet to the compression cylinder inlet; a valve outlet hole having a tapered portion included in said valve outlet, said tapered portion having a first inner diameter and a second inner diameter, said first inner diameter of said tapered portion being larger than said second inner diameter and being located at a position that is closer to said valve inlet chamber than said second inner diameter when said inlet control mechanism is installed, said second inner diameter being sufficiently small to form an air restriction against said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet, said first inner diameter of said tapered portion being sufficiently large to allow air to pass between said tapered portion of said valve outlet hole and said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which allows air to flow from said valve inlet chamber through said valve outlet; said vent passageway including a vent orifice which restricts the flow of air from said valve control chamber to said compression cylinder inlet; and said vent orifice having an orifice size which allows air to be drawn by the compressor unit from said valve control chamber to the compression cylinder at a preselected rate which causes the compressor unit to produce compressed air at less than its predetermined rate of production, said valve control chamber having a volume which enables air to be drawn through said orifice from said valve control chamber by the compressor unit over a preselected time period until air within said valve control chamber is at a reduced pressure level which enables atmospheric pressure on the valve piston assembly from within the valve inlet chamber to overcome the force of said biasing member sufficiently to move said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber through said valve outlet to enable the compressor unit to produce compressed air at its predetermined rate of production. 28. The automatic inlet control mechanism of claim 27 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet. 29. The automatic inlet control mechanism of claim 27 wherein said valve inlet includes a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 30. The automatic inlet control mechanism of claim 27 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to the compression cylinder inlet, said valve inlet including a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 31. A reciprocating air compressor unit which produces compressed air at a predetermined rate of production through the use of a piston that reciprocates within a compression cylinder, said air compressor unit comprising: an automatic inlet control mechanism for connection to said compression cylinder inlet, said automatic inlet control having a mechanism body having a valve cavity, said valve cavity having a valve control chamber and a valve inlet chamber, a valve piston assembly positioned between said valve control chamber and said valve inlet chamber and constructed to prevent air flow between said valve control chamber and said valve inlet chamber; a valve inlet positioned to allow air to flow from the atmosphere surrounding said compressor unit and into said valve inlet chamber; a valve outlet having a valve outlet hole positioned to allow air to flow from said valve inlet chamber to said compression cylinder inlet, said valve outlet hole having a size sufficient to enable said compressor unit to produce compressed air at its predetermined rate of production; said valve piston assembly including a valve piston and a valve stem, said valve piston assembly being positioned to reciprocate within said valve cavity, a biasing member having a force which moves said valve piston assembly to a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet when said compressor unit is not drawing air through said valve outlet; a vent passageway allowing air to flow between said valve control chamber and said compression cylinder inlet; said vent passageway comprising at least one source of air to said compression cylinder inlet for a period of time after said compressor unit begins to draw air though said compression cylinder inlet, following the movement of said valve piston assembly to a position which prevents air from flowing from said valve inlet chamber though said valve outlet to the compression cylinder inlet; said vent passageway including a vent orifice which restricts the flow of air from said valve control chamber to said compression cylinder inlet; and said vent orifice having an orifice size which allows air to be drawn, by the compressor unit, from said valve control chamber to said compression cylinder at a preselected rate which causes said compressor unit to produce compressed air at less than its predetermined rate of production, said valve control chamber having a volume which enables air to be drawn though said orifice from said valve control chamber by said compressor unit over a preselected time period until air within said valve control chamber is at a reduced pressure level which enables atmospheric pressure on said valve piston assembly from within said valve inlet chamber to overcome the force of said biasing member sufficiently to move said valve piston assembly away from said position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet enable said compressor unit to produce compressed air at its predetermined rate of production. 32. The reciprocating air compressor unit of claim 31 wherein said valve piston assembly includes a diaphragm positioned between said valve control chamber and said valve inlet chamber, said diaphagm being constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said diaphragm being positioned to move toward said valve control chamber when air pressure within said valve inlet chamber is greater than air pressure within said valve control chamber, said diaphragm being positioned to move toward said valve inlet chamber when air pressure within said valve control chamber is greater than the air pressure within said valve inlet chamber. 33. The reciprocating air compressor unit of claim 31 wherein said vent passageway is included within said valve piston assembly, said vent orifice being located at a position in said valve piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to said compression cylinder inlet as said valve piston assembly reciprocates within said inlet control mechanism. 34. The reciprocating air compressor unit of claim 31 wherein said valve piston assembly includes a valve stem, said vent passageway is included within said valve piston assembly and extends through said valve stem, said vent orifice being located at a position in said piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to said compression cylinder inlet as said piston assembly reciprocates within said inlet control mechanism. 35. The reciprocating air compressor unit of claim 31 wherein said valve outlet includes a valve outlet hole having a tapered portion, said tapered portion having at least a first inner diameter and a second inner diameter, said first inner diameter of said tapered portion being larger than said second inner diameter and being located at a position that is closer to said valve inlet chamber than said second inner diameter, said second inner diameter being sufficiently small to form an air restriction against said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet, said first inner diameter of said tapered portion being sufficiently large to allow air to pass between said tapered portion of said valve outlet and said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which allows air to flow from said valve inlet chamber through said valve outlet. 36. The reciprocating air compressor unit of claim 31 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet. 37. The reciprocating air compressor unit of claim 31 wherein said valve inlet includes a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 38. The reciprocating air compressor unit of claim 31 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet, said valve inlet including a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 39. The reciprocating air compressor unit of claim 31 wherein said compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from said compression cylinder inlet enters said compression cylinder, said automatic inlet control mechanism being located at least partially within said cylinder inlet chamber. 40. The reciprocating air compressor unit of claim 31 wherein: said compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from said compression cylinder inlet enters said compression cylinder, said automatic inlet control mechanism being located at least partially within said cylinder inlet chamber; and said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet. 41. A reciprocating air compressor unit which produces compressed air at a predetermined rate of production through the use of a piston that reciprocates within a compression cylinder, said air compressor unit comprising: an automatic inlet control mechanism for connection to said compression cylinder inlet, said automatic inlet control having a mechanism body having a valve cavity, said valve cavity having a valve control chamber and a valve inlet chamber, a valve piston assembly positioned between said valve control chamber and said valve inlet chamber and constructed to prevent air flow between said valve control chamber and said valve inlet chamber; a valve inlet positioned to allow air to flow from the atmosphere surrounding said compressor unit and into said valve inlet chamber; a valve outlet having a valve outlet hole positioned to allow air to flow from said valve inlet chamber to said compression cylinder inlet, said valve outlet hole having a size sufficient to enable said compressor unit to produce compressed air at its predetermined rate of production; said valve piston assembly including a valve piston and a valve stem, said valve piston assembly being positioned to reciprocate within said valve cavity, a biasing member having a force which moves said valve piston assembly to a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet when said compressor unit is not drawing air through said valve outlet; a vent passageway allowing air to flow between said valve control chamber and said compression cylinder inlet; said vent passageway comprising the primary source of air to said compression cylinder inlet for a period of time after said compressor unit begins to draw air through said compression cylinder inlet following the movement of said valve piston assembly to a position which prevents air from flowing from said valve inlet chamber through said valve outlet to the compression cylinder inlet; said vent passageway including a vent orifice which restricts the flow of air from said valve control chamber to said compression cylinder inlet; and said vent orifice having an orifice size which allows air to be drawn, by the compressor unit, from said valve control chamber to said compression cylinder at a preselected rate which causes said compressor unit to produce compressed air at less than its predetermined rate of production, said valve control chamber having a volume which enables air to be drawn through said orifice from said valve control chamber by said compressor unit over a preselected time period until air within said valve control chamber is at a reduced pressure level which enables atmospheric pressure on said valve piston assembly from within said valve inlet chamber to overcome the force of said biasing member sufficiently to move said valve piston assembly away from said position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet to enable said compressor unit to produce compressed air at its predetermined rate of production. 42. The reciprocating air compressor unit of claim 41 wherein said valve piston assembly includes a diaphragm positioned between said valve control chamber and said valve inlet chamber, said diaphragm being constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said diaphragm being positioned to move toward said valve control chamber when air pressure within said valve inlet chamber is greater than air pressure within said valve control chamber, said diaphragm being positioned to move toward said valve inlet chamber when air pressure within said valve control chamber is greater than the air pressure within said valve inlet chamber. 43. The reciprocating air compressor unit of claim 41 wherein said vent passageway is included within said valve piston assembly, said vent orifice being located at a position in said valve piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to said compression cylinder inlet as said valve piston assembly reciprocates within said inlet control mechanism. 44. The reciprocating air compressor unit of claim 41 wherein said valve piston assembly includes a valve stem, said vent passageway is included within said valve piston assembly and extends through said valve stem, said vent orifice being located at a position in said piston assembly to enable said vent orifice to restrict the flow of air from said valve control chamber to said compression cylinder inlet as said piston assembly reciprocates within said inlet control mechanism. 45. The reciprocating air compressor unit of claim 41 wherein said valve outlet includes a valve outlet hole having a tapered portion, said tapered portion having at least a first inner diameter and a second inner diameter, said first inner diameter of said tapered portion being larger than said second inner diameter and being located at a position that is closer to said valve inlet chamber than said second inner diameter, said second inner diameter being sufficiently small to form an air restriction against said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which prevents air from flowing from said valve inlet chamber through said valve outlet, said first inner diameter of said tapered portion being sufficiently large to allow air to pass between said tapered portion of said valve outlet and said valve piston assembly when said valve piston assembly is at a position within said inlet control mechanism which allows air to flow from said valve inlet chamber through said valve outlet. 46. The reciprocating air compressor unit of claim 41 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet. 47. The reciprocating air compressor unit of claim 41 wherein said valve inlet includes a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 48. The reciprocating air compressor unit of claim 41 wherein said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet, said valve inlet including a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 49. The reciprocating air compressor unit of claim 41 wherein said compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from said compression cylinder inlet enters said compression cylinder, said automatic inlet control mechanism being located at least partially within said cylinder inlet chamber. 50. The reciprocating air compressor unit of claim 41 wherein: said compression cylinder inlet includes a cylinder inlet chamber for receiving air before the air from said compression cylinder inlet enters said compression cylinder, said automatic inlet control mechanism being located at least partially within said cylinder inlet chamber; and said valve piston assembly includes a valve stem and a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when the compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to the compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet. 51. A reciprocating air compressor unit which produces compressed air at a predetermined rate of production, said reciprocating air compressor unit comprising: an automatic inlet control mechanism including a mechanism body having a valve cavity, said valve cavity having a valve control chamber and a valve inlet chamber, a valve piston assembly positioned between said valve control chamber and said valve inlet chamber and constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said valve piston assembly including a diaphragm positioned between said valve control chamber and said valve inlet chamber, said diaphragm being constructed to prevent air flow between said valve control chamber and said valve inlet chamber, said diaphragm being positioned to move toward said valve control chamber when air pressure within said valve inlet chamber is greater than air pressure within said valve control chamber, said diaphragm being positioned to move toward said valve inlet chamber when air pressure within said valve control chamber is greater than the air pressure within said valve inlet chamber; a valve inlet positioned to allow air to flow from the atmosphere surrounding said compressor unit and into said valve inlet chamber; a valve outlet having a valve outlet hole positioned to allow air to flow from said valve inlet chamber to said compression cylinder inlet, said valve outlet hole having a size sufficient to enable said compressor unit to produce compressed air at its predetermined rate of production; a valve piston and a valve stem included in said valve piston assembly, said valve piston assembly being positioned to reciprocate within said valve cavity, a biasing member having a force which moves said valve piston assembly to a position within said mechanism body which prevents air from flowing from said valve inlet chamber to said valve outlet when the compressor unit is not drawing air through said valve outlet; a vent passageway included in said valve piston assembly, said vent passageway allowing air to flow between said valve control chamber and said compression cylinder inlet; said vent passageway comprising the primary source of air to the compression cylinder inlet for a period of time after the compressor unit begins to draw air through said compression cylinder inlet following the movement of said valve piston assembly to a position which prevents air from flowing from said valve inlet chamber through said valve outlet;. a valve outlet hole having a tapered portion included in said valve outlet, said tapered portion having a first inner diameter and a second inner diameter, said first inner diameter being larger than said second inner diameter, said first inner diameter of said tapered portion being located at a position that is closer to said valve inlet chamber than said second inner diameter of said tapered portion, said second inner diameter of said tapered portion being sufficiently small to form an air restriction against said valve piston assembly when said valve piston assembly is at a position within said mechanism body which prevents air from flowing from said valve inlet chamber through said valve outlet, said first inner diameter of said tapered portion being sufficiently large to allow air to pass between said tapered portion of said valve outlet hole and said valve piston assembly when said valve piston assembly is at a position within said mechanism body which allows air to flow from said valve inlet chamber through said valve outlet; said vent passageway including a vent orifice which restricts the flow of air from said valve control chamber to said compression cylinder inlet; and said vent orifice having an orifice size which allows air to be drawn by said compressor unit from said valve control chamber to said compression cylinder at a preselected rate which causes the compressor unit to produce compressed air at less than its predetermined rate of production, said valve control chamber having a volume which enables air to be drawn through said orifice from said valve control chamber by said compressor unit over a preselected time period until air within said valve control chamber is at a reduced pressure level which enables atmospheric pressure on the valve piston assembly from within said valve inlet chamber to overcome the force of said biasing member sufficiently to move said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber through said valve outlet to enable said compressor unit to produce compressed air at its predetermined rate of production. 52. The reciprocating air compressor unit of claim 51 wherein said valve piston assembly includes a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when said compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet. 53. The reciprocating air compressor unit of claim 51 wherein said valve inlet includes a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. 54. The reciprocating air compressor unit of claim 51 wherein said valve piston assembly includes a sliding seal mounted to reciprocate along at least a portion of said valve stem to contact said valve outlet to cause said valve piston assembly to prevent air from flowing from said valve inlet chamber through said valve outlet when said air compressor unit is not drawing air through said valve outlet, the movement of said valve piston assembly away from the position at which said valve piston assembly prevents air from flowing from said valve inlet chamber and through said valve outlet to said compression cylinder inlet causing said sliding seal to move away from said valve outlet to allow air to flow to said compression cylinder inlet, said valve inlet including a filter to remove impurities from air that passes through said valve inlet and enters said valve inlet chamber. Air Compressor Description Portable reciprocating air compressor units are commonly used in a variety of applications to produce pneumatic pressure from mechanical energy that is generated from a conventional energy source such as gasoline or electricity. Such an air compressor unit normally includes a compressor pump having a reciprocating piston located within a compression cylinder, a power plant such as a motor or engine that supplies mechanical energy to the piston to cause it to reciprocate and an air reservoir for storing compressed air. The compression cylinder is configured to draw air from the environment surrounding the compressor unit and to compress the drawn air that is discharged into an air reservoir, creating a supply of air pressure having a predeterminable magnitude. A motor, engine, or other power plant is normally connected to the compressor pump to drive the reciprocating piston within a compression cylinder. During operation of the compressor unit, a rotating crankshaft, flywheel, or other assembly connected to the reciprocating piston stores a sufficient amount of angular momentum to substantially reduce the amount of high speed torque that must be exerted by the power plant to cause the piston to reciprocate. This allows the compressor pump to devote more of the total torque output of the power plant to drawing air into the compression cylinder, compressing the air and discharging the air into the air reservoir. However, prior to operation, the crankshaft does not rotate and therefore has no angular momentum. The power plant must therefore contend with a substantially increased low speed torque requirement to overcome the combined inertial and compression loaded resistance of the piston and other components of the compressor pump until operating speed is achieved. This increased low speed torque requirement can result in adverse system effects on the power plant such as stalling, overloading, or premature wear. It can also require that a larger or more sophisticated power plant be used to overcome the initial starting torque of the compressor unit, even if such a power plant is not actually needed to sustain reciprocation of the piston after the compressor has attained an operating speed. It follows that if the compression loaded resistance of the piston can be reduced prior to the compressor pump reaching its full operating speed, it becomes possible for the power plant to devote more total torque output to overcoming inertial resistance. This in turn can minimize the adverse effects of combined inertial and compression loading, can allow for the use of a smaller or less powerful and/or less sophisticated power plant or starting system, and can therefore lead to substantial reductions in energy usage by the compressor unit. SUMMARY The invention is an automatic inlet control mechanism and an air compressor unit having both a piston reciprocating within a compression cylinder and a compression cylinder inlet for which the automatic inlet control mechanism is a component. The air compressor unit includes a power plant such as a motor or engine to reciprocate the piston and an air reservoir to store compressed air. The control mechanism itself includes a mechanism body having a valve inlet, a valve cavity and a valve outlet. The valve cavity is divided into a valve control chamber and a valve inlet chamber. A valve piston assembly is positioned between the valve control chamber and the valve inlet chamber and is constructed to prevent the flow of air between the two chambers. The valve inlet allows air to flow from the atmosphere surrounding the compressor unit into the valve inlet chamber. The valve outlet allows air to flow from the valve inlet chamber to the compression cylinder inlet and has a size that allows a sufficient amount of air to flow into the compressor unit to allow the compressor unit to produce compressed air at a predetermined rate of production. The valve piston assembly includes a valve piston that is configured to reciprocate within the valve cavity. In some embodiments, the valve piston assembly includes a diaphragm that is positioned to prevent airflow between the valve control chamber and the valve inlet chamber. A biasing member provides a force that moves the valve piston assembly to a position within the inlet control mechanism that prevents air from flowing from the valve inlet to the valve outlet when the compressor unit is not drawing air through the valve outlet. This occurs, by way of example, when a compressor unit is shut down or when a continuously running compressor unit is unloaded and is idling. A vent passageway allows air to flow between the valve control chamber and the compression cylinder inlet when compression is begun at the start-up of a compressor unit or at the loading of an idling compressor unit, as the case may be. The vent passageway is at least one source of air to the compressor cylinder inlet at this time and for a period of time after the compressor unit begins to draw air through the compression cylinder inlet, following the movement of the valve piston assembly to a position which prevents air from flowing from the valve inlet chamber and through the valve outlet to the compression cylinder inlet. A vent orifice restricts the flow of air from the valve control chamber to the compression cylinder inlet. The vent orifice has a size that allows the air to be drawn by the compressor unit from the valve control chamber to the compressor cylinder at a preselected rate which causes the compressor unit to produce compressed air at less that its predetermined rate of production. The valve control chamber has a volume that enables air to be drawn through the vent orifice into the compression cylinder inlet for a preselected period of time, until the air within the control chamber is at a sufficiently reduced pressure level to allow the valve inlet chamber to overcome the force of the biasing member sufficiently to move the valve piston assembly away from the position at which air is prevented from flowing between the valve inlet chamber and the compression cylinder inlet. During the preselected period of time, the absence of air flow from the valve inlet chamber to the compression cylinder inlet allows the power plant to dedicate more of its torque output on inertial rather than compression loading. Thus, during this preselected period of time, the compressor unit increases its operating speed without subjecting the full combined load of inertial and compression loading on the power plant. This removal of initial operating torque when compression is started can allow for a substantial reduction in power plant wear or allow for a reduction in the power plant size to that which is necessary to maintain the reciprocation of the piston under load when the compressor has attained its operating speed. By the time that the compressor unit achieves an operating speed, the valve piston assembly has moved away from a position that prevents air from flowing between the valve inlet chamber and compression cylinder inlet. Air then flows unobstructed from the environment surrounding the compressor into the compression cylinder, allowing the compressor to produce air at its predetermined rate of production. Those skilled in the art will realize that this invention is capable of embodiments that are different from those shown and that details of the structure of the disclosed inlet control mechanism can be changed in various manners without departing from the scope of this invention. Accordingly, the drawings and descriptions are to be regarded as including such equivalent inlet control mechanisms as do not depart from the spirit and scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1. is a partial cross sectional view of an air compressor unit having an automatic inlet control mechanism according to one embodiment of the invention; FIG. 2A is a side cross sectional view of the automatic inlet control mechanism of FIG. 1 in a fully closed position; FIG. 2B is a side cross sectional view of the automatic inlet control mechanism of FIG. 1 in an intermediate position; FIG. 2C is a side cross sectional view of the automatic inlet control mechanism of FIG. 1 in an open position; FIG. 3 is an exploded perspective view of the automatic inlet control mechanism of FIGS. 2A C; FIG. 4 is a partial cross sectional view of an air compressor unit having an automatic inlet control mechanism according to one embodiment of the invention; FIG. 5 is a partial cross sectional view of an air compressor unit having an automatic inlet control mechanism according to one embodiment of the invention; FIG. 6A is a side cross sectional view of the automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 6B is a side cross sectional view of the inlet control mechanism of FIG. 6A in an intermediate position; FIG. 6C is a side cross sectional view of the inlet control mechanism of FIG. 6A in an open position; FIG. 7A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 7B is a side cross sectional view of the inlet control mechanism of FIG. 7A in an intermediate position; FIG. 7C is a side cross sectional view of the inlet control mechanism of FIG. 7A in an open position; FIG. 8A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 8B is a side cross sectional view of the inlet control mechanism of FIG. 8A in an intermediate position; FIG. 8C is a side cross sectional view of the inlet control mechanism of FIG. 8A in an open position; FIG. 9A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 9B is a side cross sectional view of the inlet control mechanism of FIG. 9A in an intermediate position; FIG. 9C is a side cross sectional view of the inlet control mechanism of FIG. 9A in an open position; FIG. 10A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 10B is a side cross sectional view of the inlet control mechanism of FIG. 10A in an intermediate position; FIG. 10C is a side cross sectional view of the inlet control mechanism of FIG. 10A in an open position; FIG. 11A is a cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a closed position; FIG. 11B is a cross sectional view of the inlet control mechanism of FIG. 11A in an open position; FIG. 12A is a cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a closed position; FIG. 12B is a cross sectional view of the inlet control mechanism of FIG. 12A in an open position; FIG. 13A is a cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a closed position; FIG. 13B is a cross sectional view of the inlet control mechanism of FIG. 13A in an open position; FIG. 14A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention at a LOW setting; FIG. 14B is a side cross sectional view of the inlet control mechanism of FIG. 14A at a MEDIUM setting; FIG. 14C is a side cross sectional view of the inlet control mechanism of FIG. 14A at a HIGH setting; FIG. 15A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention at a LOW setting; FIG. 15B is a side cross sectional view of the inlet control mechanism of FIG. 15A at a MEDIUM setting; FIG. 15C is a side cross sectional view of the inlet control mechanism of FIG. 15A at a HIGH setting; FIG. 15D is a magnified view of the inlet control mechanism of FIG. 15A at the LOW setting; FIG. 16A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention at a low setting; FIG. 16B is a side cross sectional view of the inlet control mechanism of FIG. 16A at an intermediate setting; FIG. 16C is a side cross sectional view of the inlet control mechanism of FIG. 16A at a high setting; FIG. 16D is a magnified view of the adjustment mechanism of FIG. 16A; FIG. 17A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a closed position; FIG. 17B is a side cross sectional view of the inlet control mechanism of FIG. 17A in an intermediate position; FIG. 17C is a side cross sectional view of the inlet control mechanism of FIG. 17A in an open position; FIG. 18A is a partial cross sectional view of an air compressor unit having an automatic inlet control mechanism according to one embodiment of the invention; FIG. 18B is a magnified side cross sectional view of the automatic inlet control mechanism of FIG. 18A; FIG. 19A is a partial cross sectional view of an air compressor unit having an automatic inlet control mechanism according to one embodiment of the invention; FIG. 19B is a magnified side cross sectional view of the automatic inlet control mechanism of FIG. 19A; FIG. 20A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a closed position; FIG. 20B is a side cross sectional view of the inlet control mechanism of FIG. 20A in a closed, intermediate position; FIG. 20C is a side cross sectional view of the inlet control mechanism of FIG. 20A in an open position; FIG. 21A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 21B is a side cross sectional view of the inlet control mechanism of FIG. 21A in a closed, intermediate position; FIG. 21C is a side cross sectional view of the inlet control mechanism of FIG. 21A in a fully open position; FIG. 22A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 22B is a side cross sectional view of the inlet control mechanism of FIG. 22A in a fully open position; FIG. 23A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 23B is a side cross sectional view of the inlet control mechanism of FIG. 23A in a fully open position; FIG. 24A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 24B is a side cross sectional view of the inlet control mechanism of FIG. 24A in a fully open position; FIG. 25A is a front perspective view of an individual labyrinth restrictor of FIGS. 24A and B; FIG. 25B is a rear view of the labyrinth restrictor of FIG. 25A; FIG. 25C is a rear perspective view of the labyrinth restrictor of FIG. 25A; FIG. 25D is a side view of the labyrinthine restrictor of FIG. 25A; FIG. 26A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 26B is a magnified side cross sectional view of the restriction in the vent passageway of the inlet control mechanism of FIG. 26A; FIG. 26C is a side cross sectional view of the inlet control mechanism of FIG. 26A in a fully open position; FIG. 27A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention in a fully closed position; FIG. 27B is a magnified side cross sectional view of the restriction in the vent passageway of the inlet control mechanism of FIG. 27A; FIG. 27C is a side cross sectional view of the inlet control mechanism of FIG. 27A in a fully open position; FIG. 28A is a side cross sectional view of an automatic inlet control mechanism according to one embodiment of the invention at a closed position; FIG. 28B is a side cross sectional view of the inlet control mechanism of FIG. 28A at an intermediate position; FIG. 28C is a side cross sectional view of the inlet control mechanism of FIG. 28A at an open position; FIG. 29A is a side cross sectional view of a compressor pump having an automatic inlet control mechanism according to one embodiment of the invention in a closed position; FIG. 29B is a side cross sectional view of the compressor pump of FIG. 29A in an open position; FIG. 30A is a side cross sectional view of a compressor pump having an automatic inlet control mechanism according to one embodiment of the invention in a closed position; and FIG. 30B is a side cross sectional view of the compressor pump of FIG. 30A in an open position. DETAILED DESCRIPTION Referring to the drawings, similar reference numerals are used to designate the same or corresponding parts throughout the several embodiments and figures. In some drawings, some specific embodiment variations in corresponding parts are denoted with the addition of lower case letters to reference numerals. FIG. 1 depicts a typical wheeled portable reciprocating air compressor unit 32a. The compressor unit 32a includes a compressor pump 48a mounted on an air reservoir 50 that forms a structural chassis to support the various components of the compressor unit 32a. The compressor unit 32a is supported with one or more legs 52 and wheels 54 that are positioned near the ends of the air reservoir 50. A handle 56 allows one end of the compressor unit 32a to be lifted off of its legs 52 to enable the compressor unit 32a to be moved about on its wheels 54. An electric motor 58 and pressure switch 60 are also mounted on the air reservoir 50. Although FIG. 1 depicts an electric motor, it will be appreciated that other types of power plants can be similarly implemented and are within the contemplated scope of the invention. The electric motor 58 is connected to draw electrical current from an electrical circuit (not shown) when the pressure switch 60 assumes an ON position. When the pressure switch 60 assumes an ON position, the motor 58 drives a pulley 34 connected to a crank shaft 62 on the compressor pump 48a with a drive belt 65. Although the crank shaft 62 is depicted as being belt driven in FIG. 1, it will be appreciated that the invention can be similarly implemented into a direct drive system in which rotational energy is transferred directly from a motor or other power plant to the crankshaft of a compressor pump through a shaft, gear, or other connective mechanism. In some embodiments, the pulley 34 can also function as a flywheel or, alternatively a separate flywheel (not shown) can be connected to the crankshaft 62. The pressure switch 60 is configured to be responsive to air pressure within the air reservoir 50 and to allow operation of the electric motor 58 when the magnitude of the pressure within the air reservoir 50 falls below a predetermined magnitude. A screen guard 66 encloses the drive belt 65 and pulley 34. Although FIG. 1 depicts an air compressor unit 32a having basic compressor components arranged in a typical single reservoir configuration, it will be appreciated that other portable compressor unit configurations are also possible. Such compressor units include those having upright standing, pancake, spherical or multiple air reservoirs and/or liftable, all legged, tailored, wheelbarrow, or sliding chassis configurations. Other similar variations are also possible and are contemplated to be included within the types of portable reciprocating air compressor units that are suitable for use with the invention. FIG. 1 includes a partial cross sectional view of internal components within the compressor pump 48a to further illustrate their relation to the rest of the compressor unit 32a. An automatic inlet control mechanism 36a is connected to a threaded inlet port 40a of a compression cylinder inlet 38a. The inlet control mechanism 36a and compression cylinder inlet 38a allow air to enter the compressor pump 48a during each reciprocation of a piston 42 that is located within a compression cylinder 44. The inlet port 40a is positioned to channel air from the inlet control mechanism 36a to a cylinder inlet chamber 46a which receives air before the air is channeled into the compression cylinder 44 through a cylinder inlet valve 64 positioned within a cylinder inlet hole 66. The cylinder inlet hole 66 and cylinder inlet valve 64 can be included as part of a valve plate 68 that is positioned between the cylinder inlet chamber 46a and compression cylinder 44. The cylinder inlet valve 64 is unidirectional in that it only allows air to flow through the cylinder inlet hole 66 from the cylinder inlet chamber 46a when, during an intake stroke (downward as depicted in FIG. 1) of the piston 42, the piston 42 draws air into the compression cylinder 44. During a compression stroke (upward as depicted in FIG. 1) of the piston 42, the cylinder inlet valve 64 closes to prevent air from flowing from the compression cylinder 44, through the cylinder inlet hole 66 and back into and through the cylinder inlet chamber 46a. The electric motor 58 effects reciprocation of the piston 42 by turning the pulley 34 and crankshaft 62 of the compressor pump 48a with the drive belt 65. The crankshaft 62 in turn causes reciprocation of a piston shaft 70 which drives the piston 42, the piston shaft 70 being connected to the piston 42 with a piston pin 72. The amount of work that the electric motor 58 must perform to cause the reciprocation of the piston 42 ultimately depends on the amount of air that is drawn through the compression cylinder inlet 38a during each piston reciprocation. This is due to the fact that the amount of air that is drawn through the compression cylinder inlet 38a ultimately determines the amount of air that the piston 42 can draw into the compression cylinder 44 and compress during each reciprocation. Thus, the amount of energy that the electric motor 58 must exert to run the compressor unit 32a is directly dependent on the amount of air that is permitted to pass through the automatic inlet control mechanism 36a during each reciprocation. A compression cylinder outlet 74a is positioned to receive air that has been compressed in the compression cylinder 44 and to channel air from the compression cylinder 44 out of the compressor pump 48a during each compression stroke of the piston 42. The compression cylinder outlet 74a includes a cylinder outlet chamber 76a for receiving air that has been compressed in the compression cylinder 44, an outlet port 78, and a unidirectional cylinder outlet valve 80 located in a cylinder outlet hole 82 for channeling air into the cylinder outlet chamber 76a. The cylinder outlet hole 82 and cylinder outlet valve 80 can be included as part of the valve plate 68 that is positioned between the compression cylinder 44 and cylinder outlet chamber 76a. The cylinder outlet valve 80 is unidirectional in that it only allows air to flow through the cylinder outlet hole 82 and into the cylinder outlet chamber 76a when, during a compression stroke of the piston 42, the piston 42 expels air from the compression cylinder 44. During an intake stroke of the piston 42, the cylinder outlet valve 80 closes to prevent air from flowing from the cylinder outlet chamber 76a back through the cylinder outlet hole 82 and into the compression cylinder 44. A discharge tube 84 is connected to the outlet port 78 to channel compressed air from the compressor pump 48a to the air reservoir 50. A check valve 86 is positioned at the end of the discharge tube 84 to allow air to flow from the discharge tube 84 into the air reservoir 50 while preventing backflow from the reservoir 50 into the discharge tube 86 and to prevent loss of air pressure from within the reservoir 50. The pressure switch 60 is connected to the electric motor 58 and is mounted at a location that allows the pressure switch 60 to sense the pressure of air contained within the air reservoir 50. As air is forced into the air reservoir 50, pressure in the air reservoir 50 increases. When the air pressure within the air reservoir 50 reaches a predetermined maximum magnitude of pressurization, the pressure switch 60 assumes an OFF position since additional air compression is not necessary. Once the air pressure within the air reservoir 50 falls below a minimum predetermined magnitude, the pressure switch 60 assumes an ON position, allowing the electric motor 58 to cause the compressor pump 48a to add compressed air to the air reservoir 50 until the air pressure within the air reservoir 50 rises to the predetermined maximum magnitude at which time the pressure switch 60 returns to an OFF position. However, the amount of air that is compressed, and consequently the amount of work that is performed by the electric motor 58 with each reciprocation of the piston 42, will continue to depend on the amount of air that is permitted to enter the compression cylinder through the compression cylinder inlet 38a Since it is the electric motor 58 that is responsible for turning the drive belt 65 and pulley 34 to effect reciprocation of the piston 42, the electric motor 58 must also provide sufficient energy to contend with additional loads resulting from combined inertial and compression loaded resistance of the piston 42 and other components of the compressor pump 48a. Thus, if air is permitted to freely enter the compression cylinder 44 through the compression cylinder inlet 38a, the electric motor 58 must contend with an increased starting torque that includes both with the compression loaded resistance of the piston 42 and the combined inertial resistance of the piston 42 and other components of the compressor unit 32a. If air is restricted from entering the compression cylinder 44 through the compression cylinder inlet 38a, the electric motor 58 need only contend with the combined inertial resistance of the piston 42 and other components of the compressor unit 32a once air is removed from the compression cylinder inlet 38a and compression cylinder 44. During operation, the rotating crankshaft 62, pulley 34, drive belt 65, and other components of the compressor unit 32a rotate at an operating speed and therefore store a sufficient amount of angular momentum to substantially reduce the amount of high speed torque that must be exerted by the electric motor 58 to maintain the reciprocating motion of the piston 42. This allows the compressor pump 48a to devote more of the total torque output of the electric motor 58 to drawing air into the compression cylinder 44, compressing the air, and discharging the air into the air reservoir 50. However, prior to operation, the crankshaft 62, pulley 34, and other components do not rotate at an operating speed and therefore do not provide angular momentum that to assist the electric motor 58 in causing the reciprocation of the piston 42 while the piston is compression loaded. Therefore, in order to reduce the total torque output required from the electric motor 58 at the start of operation, i.e. in order to reduce the starting torque, it is necessary to temporarily remove the compression loaded resistance of the piston 42 until the motor 58 overcomes the inertial resistance of the compressor pump 48a, allowing the compressor pump 48a to first reach a full operating speed and restore angular momentum to the crankshaft 62, pulley 34, and other components of the compressor unit 32a. The automatic inlet control mechanism 36a is configured to allow for the temporary removal of piston compression loading until the compressor pump 48a reaches a full operating speed. FIG. 1 depicts the inlet control mechanism 36a connected to the inlet port 40a of the compressor unit 32a, the inlet control mechanism 36a being shown in a closed position. A magnified view of the inlet control mechanism 36a of FIG. 1 is depicted in FIG. 2A. An exploded view depicting the components of the inlet control mechanism is depicted in FIG. 3. Comparing FIGS. 1, 2A, and 3, the control mechanism 36a includes a mechanism body 88a having a valve cavity 90a that is divided into a valve control chamber 92a and a valve inlet chamber 94a. The mechanism body 88a can include an inlet segment 87a and a control segment 89a that can be detached from each other prior to assembly to allow for the installation of a valve piston assembly 96a and/or other mechanism components into the valve cavity 90a. A male connector 91 on the inlet segment 87a allows for engagement with a female connector 93 on the control segment 89a, the male connector 91 and female connector 93 being snap connected when the mechanism body 88a is assembled. When the mechanism body 88a is assembled, the valve piston assembly 96a is positioned between the valve control chamber 92a and valve inlet chamber 94a and is configured to reciprocate within the valve cavity 90a while preventing air from flowing directly between the valve control chamber 92a and valve inlet chamber 94a. A valve inlet 98a extends through the mechanism body 88a and allows air to flow from the atmosphere surrounding the compressor unit 32a into the valve inlet chamber 94a. The valve inlet 98a can include a filter 100 to remove impurities from air that passes through the valve inlet 98a before the air enters the valve inlet chamber 94a. A valve outlet 102a includes a valve outlet hole 104a positioned to allow air to flow from the valve inlet chamber 94a into the compression cylinder inlet 38a. The valve outlet 102a is threaded to allow for connection to the inlet port 40a of the compression cylinder inlet 38a. The valve outlet hole 104a is sized to allow a sufficient amount of air to flow from the inlet control mechanism 36a to the compression cylinder inlet 38a to allow the compressor unit 32a to produce air at its predetermined rate of production. The valve outlet hole 104a can further include a tapered portion 103a. The valve piston assembly 96a includes a valve piston 108a, a diaphragm 106, a valve stem 110a, and a valve stem seal 116a that are configured to reciprocate within the valve cavity 90a along a valve axis 112. Within the valve cavity 90a, the diaphragm 106 forms a seal between the inside surface of the mechanism body 88a and the rest of the valve piston assembly 96a to prevent air from moving directly between the valve control chamber 92a and valve inlet chamber 94a. A spring biasing member 114a produces a force that biases the valve piston assembly to move toward the valve inlet chamber 94a and away from the valve control chamber 92a to a position within the inlet control mechanism 36a in which the valve stem seal 116a contacts the inside surface of the mechanism body 88a to prevent air from flowing from the valve inlet chamber 94a through the valve outlet 102a. A vent passageway 118a extends through the valve stem 110a, opening to the valve control chamber 92a and allowing for the communication of air between the valve control chamber 92a and valve outlet 102a or compression cylinder inlet 38a through a stem hole 120. An orifice 122a forms a restriction to air that flows through the vent passageway 118a, delaying the rate at which air can communicate between the valve control chamber 92a and valve outlet 102a or compression cylinder inlet 38a. The valve stem 110a also includes a sliding surface 124 on which the valve stem seal 116a reciprocates in response to the movement of the valve stem 110a with the valve piston assembly 96a and/or the air pressure differential between the compression cylinder inlet 38a and valve inlet chamber 94a. The valve stem seal 116a can be constructed of rubber, teflon, a resilient polymer, or any other material that allows for sliding or reciprocation of the valve stem seal 110a along the sliding surface 124 while also allowing for the creation of a seal between the sliding surface of the valve stem 110a and the inside surface of the mechanism body 88a when the piston assembly is in a position within the valve cavity 90a that prevents air from flowing from the valve inlet chamber 94a to the compression cylinder inlet. A lip 126 and an expanded radius 128 are positioned at opposite ends of the sliding surface 124 to restrict the reciprocating movement of the valve stem seal 116a. To better understand the operation of the automatic inlet control mechanism 36a, consider the air compressor unit 32a prior to operation, as depicted in FIGS. 1 and 2A. Electric current from an electric circuit (not shown) is not connected to the pressure switch 60 since the compressor unit 32a is either not in use (power OFF) or is instead in use (power ON) but air pressure within the air reservoir 50 is greater than a predetermined minimum magnitude. In either case, the pressure switch 60 does not permit electric current to flow to reach the electric motor 58. The electric motor 58 does not cause rotation of the drive belt 65, pulley 34, and drive shaft 62. Therefore, the piston 42 does not reciprocate within the compression cylinder 44 and air is neither drawn through the cylinder inlet valve 64 nor forced through the cylinder outlet valve 80 in the compressor pump 48a. The spring biasing member 114a forces the valve piston assembly 96a away from the valve control chamber 92a and toward the valve inlet chamber 94a. The valve stem seal 116a, having a larger diameter than part of the tapered portion 103a of the valve outlet 102a, seals between the valve outlet 102a and sliding surface 124 of the valve stem 110a as the expanded radius 128 forces the valve stem seal 116a against the tapered portion 103a under the force of the spring biasing member 114a. The resulting seal between the valve stem 110a and valve outlet 102a prevents air from the atmosphere surrounding the air compressor unit from 32a entering the compression cylinder 44 through the valve inlet chamber 94a. Now consider the compressor unit 32a when electric current is initially connected to the pressure switch 60 (power ON) and/or when pressure within the air reservoir 50 falls below a predetermined minimum magnitude while power is ON. The pressure switch 60 senses the low air pressure within the air reservoir 50 and in response connects the electric motor 58 to electric current from the electrical circuit. The motor 58 begins to rotate the drive belt 65, pulley 34, and drive shaft 62 to initiate reciprocation of the piston 42. However, the motor 58 must contend with the inertial resistance of each of these components. In addition, the motor 58 must also contend with any air that is present within the compressor pump 48a or discharge tube 84. However, the valve stem 10a and valve stem seal 116a prevent air from the atmosphere surrounding the compressor unit 32a from entering the compressor pump 48a through the inlet control mechanism 36a. As the piston 42 begins to reciprocate, remaining air is quickly drawn out of the cylinder inlet chamber 46a and forced through the cylinder outlet valve 80 into the cylinder outlet chamber 76a and discharge tube 84. During a very short time interval, the speed of the initial rotation of the drive belt 65, pulley 34, and drive shaft 62 and the speed of reciprocation of the piston 42 is very low. During this very short interval, the electric motor 58 must bear the combined inertial and compression loaded resistance of the piston 42 and other components. Thus, during this short interval, the combined loads cause the electric motor 58 to experience a high current draw or "current spike." However, after a very small number of piston reciprocations, most of the air initially present in the cylinder inlet chamber 46a is removed by the reciprocating piston 42. Most of the air is removed from the cylinder inlet chamber 46a while the piston 42 reciprocates at a very low relative speed. Since the valve stem 110a and valve stem seal 116a prevent additional amounts of air from entering the compressor pump 48a from the atmosphere through the valve inlet 98a of the inlet control mechanism 36a, air drawn through the vent passageway 118a from the valve control chamber 92a becomes the primary source of air to the compression cylinder inlet 38a as the speed of the electric motor 58 and the reciprocation rate of the piston 42 begin to increase. The air drawn through the vent passageway 118a from the valve control chamber 92a continues to be the primary source of air to the compression cylinder inlet 38a as long as the valve piston assembly 96a is in a position that prevents air from flowing from the valve inlet chamber 94a to the compressor cylinder inlet 38a. However, the orifice 122a forms a restriction that limits the rate at which air can be drawn into the compression cylinder inlet 38a through the vent passageway 118a. As a result of this restriction, the amount of air that can be drawn into the compression cylinder inlet 38a from the valve control chamber 92a during a given time interval is very small compared to the amount of air that can be drawn from the valve inlet chamber 94a when the valve piston assembly 96a is in a position that does not prevent air from flowing between the valve inlet chamber 94a and compression cylinder inlet 38a. Consequently, compression loading of the piston 42 is greatly reduced as long as the valve control chamber 92a remains the primary source of air to the compression cylinder inlet 38a. This reduction in compression loading of the piston 42 allows the electric motor 58 to devote more total torque output to overcoming inertial resistance as the speed of the motor 58 and reciprocation rate of the piston 42 increase. Since compression loading of the piston 42 is reduced, the compressor unit 32a produces compressed air at less than its predetermined rate of production. However, the reduction in initial compression loading can be effective in significantly reducing wear of the electric motor 58 and/or can allow the motor 58 to be reduced in size to only that which is necessary to maintain the reciprocation of the piston 42 once the piston has achieved an operating speed. This can in turn allow for a substantial reduction in wear, component cost, or energy usage. As the speed of the motor 58 and the reciprocation rate of the piston 42 continue to increase, air continues to be drawn through the vent passageway 118a, orifice 122a, and stem hole 120 from the valve control chamber 92a into the cylinder inlet chamber 46a. This reduces the amount of air pressure that is present within the valve control chamber 92a. Atmospheric pressure within the valve inlet chamber 94a is maintained by air communication through the valve inlet 98a. The sealed separation between the valve inlet chamber 94a and valve control chamber 92a created by the diaphragm 106 results in a pressure differential between the chambers that begins to force the diaphragm 106 and the rest of the valve piston assembly 96a, against the force of the spring biasing member 114a and toward the valve control chamber 92a to an intermediate position within the valve cavity 90a. FIG. 2B depicts the inlet control mechanism 36a in which the valve piston assembly 96a is located at such an intermediate position within the valve cavity 90a. As the valve stem 110a moves toward the valve control chamber 92a, very little pressure continues to occupy the compression cylinder inlet 38a though atmospheric pressure continues to exist within the valve inlet chamber 94a. This creates a pressure differential that continues to force the valve stem seal 116a against the tapered portion 103a of the valve outlet 102a. As the valve stem 110a moves with the rest of the valve piston assembly 96a toward the valve control chamber 92a, the valve stem seal 116a slides against the sliding surface 124 of the valve stem 110a, maintaining the seal between the valve stem 110a and the inside surface of the mechanism body 88a while continuing to prevent air from flowing from the valve inlet chamber 94a and compression cylinder inlet 38a. The valve stem 110a is normally configured so that the valve stem seal 116a continues to seal between the valve stem 110a and mechanism body 88a until the electric motor 58 and compressor unit 32a achieve an operating speed. As the piston 42 continues to draw air from the valve control chamber 92a, the pressure differential between the valve inlet chamber 94a and compression cylinder inlet 38a continues to force the valve stem seal 116a against the tapered portion 103a of the valve outlet 102a until the valve stem seal 116a, sliding across the sliding surface 124, contacts the lip 126 of the valve stem 110a. The lip 126 forces the valve stem seal 116a away from the tapered portion 103a of the valve outlet 102a. The valve piston assembly 96a continues to move toward the valve control chamber 92a until the air in the valve control chamber 92a is at a sufficiently reduced pressure level that enables atmospheric pressure in the valve inlet chamber 94a to overcome the force of the spring biasing member 114a sufficiently to move the valve piston 108a to contact the mechanism body 88a as shown in FIG. 2C. This movement creates an air space 130a allowing air from the valve inlet chamber 94a and atmosphere to enter the compression cylinder inlet 38a. However, by the time that the valve stem seal 116a moves away from the mechanism body 88a, the electric motor 58 and compressor unit 32a will normally have achieved an operating speed and are therefore better equipped to deal with additional compression loading against the piston 42. The amount of time required for the valve piston assembly 96a to move to a position, such as that depicted in FIG. 2C, that does not prevent air from flowing from the valve inlet chamber 94a through the valve outlet 102a into the compression cylinder inlet 38a depends on the rate at which air can be drawn by the piston 42 from the valve control chamber 92a, which in turn depends on the size of the orifice 122a. Thus, the amount of time during which the automatic inlet control mechanism 36a removes compression loading on the piston depends on the size or effective size of the vent restriction of air flowing through the vent passageway 118a. This amount of time can be preselected by incorporating an orifice or other restriction having a size or effective size that corresponds to the rate of allowed air flow allowing for sufficient time for the compressor unit 32a to achieve a desired operating speed while unloaded. It will be appreciated that the invention can be similarly implemented in continuously operated compressor units. Referring now to FIG. 4, an air compressor unit 32b is depicted in which a pilot valve 132b takes the place of a pressure switch to enable the electric motor 58 to run continuously without continuously causing the compressor pump 48b to add compressed air to the air reservoir 50. The pilot valve 132b is positioned on the air reservoir 50 and is configured to be responsive to the magnitude of air pressure that is contained within the air reservoir 50. The pilot valve 132b communicates pneumatically through a pilot tube 134 with an inlet unloader 136 that is positioned on the compressor pump 48b. The inlet unloader 136 includes an unloader pin 138 that is positioned to extend to and retract from the inlet unloader 136 to interfere with the operation of the cylinder inlet valve 64 and to prevent further reservoir pressurization when the reservoir 50 is fully pressurized to a predetermined maximum magnitude of pressurization. Consider the air compressor unit 32b when, due to usage of air pressure by devices connected to the compressor unit 32b, the magnitude of air pressure contained within the air reservoir 50 falls below a predetermined minimum magnitude. The electric motor 58 will be at an idle speed, as explained below. The pilot valve 132b senses low pressure within the reservoir 50 and assumes an OFF condition. In response, the pilot valve 132b pneumatically communicates the OFF condition to the inlet unloader 136 by removing a pneumatic pressure signal from the pilot tube 134. In turn, the inlet unloader 136 retracts the unloader pin 138 away from the inlet valve 64, allowing the inlet valve 64 to operate to permit air to be drawn from the cylinder inlet chamber 46b and through the cylinder inlet hole 66 and into the compression cylinder 44 during each intake stroke of the piston 42, while preventing air from being expelled from the compression cylinder 44 back through the cylinder inlet chamber 46b during each compression stroke of the piston 42. The pilot valve 132b will continue to prevent the inlet unloader 136 from interfering with the inlet valve 64 as long as air pressure within the reservoir 50 remains below a predetermined maximum magnitude which is larger than the predetermined minimum magnitude. Since the motor 58 runs continuously, the amount of air that is compressed with each reciprocation of the piston 42 and the amount of torque output required to continue reciprocation of the piston 42 will continue to depend on the amount of air that is permitted by the automatic inlet control mechanism 32b to enter the compression cylinder inlet 38b. When the pilot valve 132b initially removes the pneumatic pressure signal from the pilot tube 134 to cause retraction of the unloader pin 138, the valve piston assembly 96b is normally in a position in which the valve stem seal 116 prevents air from moving from the valve inlet chamber 94b through the valve outlet 102b and into the cylinder inlet chamber 46b. Air from the valve control chamber 92b becomes the primary source of air to the compression cylinder 44 for an interval of time until which the valve piston assembly 96b moves to a position that allows for air to move from the valve inlet chamber 94b through the valve outlet 102b into the cylinder inlet chamber 46b. Since during this interval, the amount of air that can flow from the valve control chamber 92b into the compression cylinder inlet 38b is restricted by the orifice 122b, there is a substantial reduction in the amount of compression loading of the piston 42. As the piston 42 continues to reciprocate, the valve piston assembly 96b gradually moves from an intermediate position that does not permit air to flow between the valve inlet chamber 94b and valve outlet 102b to an intermediate position that does permit airflow between the valve inlet chamber 94b and valve outlet 102b, and then continues to move to a fully open position that allows greater air flow to the compression cylinder inlet 38b. This has the effect of allowing full compression loading to be reached gradually rather than suddenly. Although the compressor unit 32b is a continuous-run system, such smooth operation can nevertheless substantially reduce wear, and can allow for the use of a smaller or less powerful power plant due to the more gradual compression loading. This further allows for reductions in both apparatus cost and energy consumption. Now consider the same air compressor unit 32b when, due to the compression of air by the piston 42, the magnitude of air pressure contained within the reservoir 50 rises above the predetermined minimum magnitude. The pilot valve 132b continues to pneumatically communicate the OFF condition to the inlet unloader 136 until the air pressure within the air reservoir 50 rises above the predetermined maximum magnitude. When the air pressure contained within the reservoir 50 rises above the predetermined maximum magnitude, the pilot valve 132b senses that the reservoir 50 is fully pressurized and assumes an ON condition. In response, the pilot valve 132b pneumatically communicates the ON condition to the inlet unloader 136 by adding a pneumatic pressure signal through the pilot tube 134. In turn, the inlet unloader 136 extends the unloader pin 138 to contact the inlet valve 64 and to prevent the inlet valve 64 from closing during each compression stroke of the piston 42. Although the open inlet valve 64 allows air to be drawn from the valve inlet chamber 94b and cylinder inlet chamber 46b through the inlet hole 66 into the compression cylinder 44 during each intake stroke of the piston 42, the piston 42 also expels air from the compression cylinder 44 back through the inlet hole 66 into the cylinder inlet chamber 46b and valve inlet chamber 94b, valve inlet 98b, and into the environment during each compression stroke as long as the inlet unloader 136 prevents the cylinder inlet valve 64 from closing. Since the open inlet valve 64 prevents the piston 42 from removing air pressure from the cylinder inlet chamber 46b and valve outlet 102b, air is no longer drawn from the valve control chamber 92b through the vent passageway 118b and orifice 122b. Consequently, the spring biasing member 114b is free to force the valve piston assembly 96b back toward the valve outlet 102b. Moreover, since air pressure is restored within the valve outlet 102b and compression cylinder inlet 38b, air is free to return to the valve control chamber 92b as the valve piston 108b moves toward the valve inlet chamber 94b. This continues until the valve piston assembly 96b returns to a position that prevents air from moving from the valve inlet chamber 94b to the valve outlet 102b. However, the piston 42 continues to be prevented from drawing significant amounts of air from the valve control chamber 92b as long as the unloader pin 138 prevents the inlet valve 64 from closing during each compression stroke of piston 42. The motor 58 then runs continuously at an idle speed, as explained below. However, the compressor pump 48b will be prevented from adding air pressure to the reservoir 50, regardless of the amount of electric current drawn by the motor 58 from the electrical circuit, the amount of air that is permitted by the automatic inlet control mechanism 36b to enter through the compression cylinder inlet 38b, or the amount of torque output that is available from the electric motor 58, until the pilot valve 132b again senses that reservoir pressure is below the predetermined minimum magnitude and accordingly removes its pneumatic pressure signal from the pilot tube 134. It will be further appreciated that the invention can be implemented into compressor units having different types of power plants. For example, FIG. 5 depicts a continuous dri |