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The present invention provides a head valve assembly for a pneumatic fastener including a piston assembly reciprocated within a cylinder assembly for driving a fastener and a housing having an end cap for at least partially enclosing the head valve assembly. The head valve assembly includes a valve

The present invention provides a head valve assembly for a pneumatic fastener including a piston assembly reciprocated within a cylinder assembly for driving a fastener and a housing having an end cap for at least partially enclosing the head valve assembly. The head valve assembly includes a valve piston for causing supply pressure to be ported to the piston assembly for moving the piston assembly within the cylinder assembly from a non-actuated position to an actuated position for driving the fastener. Further, an inner cap is disposed within the end cap around the valve piston. The inner cap includes an inlet port for porting pressure to the valve piston. In addition, a main seal is coupled to the valve piston for sealing the cylinder assembly from supply pressure while pressure is ported to the valve piston by the inner cap for holding the piston assembly in the non-actuated position. The main seal seals pressure ported to the valve piston by the inner cap from supply pressure ported to the piston assembly.

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What is claimed is: 1. A head valve assembly for a pneumatic fastener including a piston assembly reciprocated within a cylinder assembly for driving a fastener and a housing having an end cap for at least partially enclosing the head valve assembly, the head valve assembly comprising: a valve pist

What is claimed is: 1. A head valve assembly for a pneumatic fastener including a piston assembly reciprocated within a cylinder assembly for driving a fastener and a housing having an end cap for at least partially enclosing the head valve assembly, the head valve assembly comprising: a valve piston for causing supply pressure to be ported to the piston assembly for moving the piston assembly within the cylinder assembly from a non-actuated position to an actuated position for driving the fastener; an inner cap disposed within the end cap around the valve piston, the inner cap including an inlet port for porting pressure to the valve piston; and a main seal coupled to the valve piston for sealing the cylinder assembly from supply pressure while pressure is ported to the valve piston by the inner cap for holding the piston assembly in the non-actuated position, wherein the main seal seals pressure ported to the valve piston by the inner cap from supply pressure ported to the piston assembly. 2. The head valve assembly as claimed in claim 1, wherein the inner cap further comprises an exhaust port for porting exhaust from the head valve assembly. 3. The head valve assembly as claimed in claim 1, wherein the inner cap is formed of a lubricious plastic. 4. The head valve assembly as claimed in claim 1, wherein the main seal comprises a lip seal for forming a seal with the inner cap. 5. The head valve assembly as claimed in claim 1, further comprising a snap-lock mechanism for coupling the main seal to the piston valve. 6. The head valve assembly as claimed in claim 5, wherein the snap-lock assembly comprises a plurality of legs extending from the main seal and a plurality of leg receivers disposed in an inner surface of the valve piston, each of the plurality of leg being received in a corresponding one of the plurality of leg receivers for coupling the main seal to the valve piston. 7. The head valve assembly as claimed in claim 6, wherein the piston assembly includes a projection, the plurality of legs for receiving and retaining the projection upon return of the piston assembly from the actuated position to the non-actuated position. 8. The head valve assembly as claimed in claim 6, further comprising a compression spring for biasing the valve piston toward the piston assembly and causing the main seal to seal the cylinder assembly from supply pressure. 9. The head valve assembly as claimed in claim 8, wherein the compression spring traps the plurality of legs for preventing the main seal from separating from the piston valve by the piston assembly as the piston assembly moves from the non-actuated position to the actuated position. 10. The head valve assembly as claimed in claim 1, wherein the main seal provides shook absorption to the piston assembly. 11. The head valve assembly as claimed in claim 1, further comprising a lip seal disposed between the valve piston and the inner cap. 12. A pneumatic fastener, comprising: a housing; a cylinder assembly disposed within the housing; a piston assembly reciprocated within the cylinder assembly for driving a fastener; an end cap coupled to the housing; a head valve assembly at least partially disposed within the end cap, the head valve assembly including: a valve piston for causing supply pressure to be ported to the piston assembly for moving the piston assembly within the cylinder assembly from a non-actuated position to an actuated position for driving the fastener; an inner cap disposed within the end cap around the valve piston, the inner cap including an inlet port for porting pressure to the valve piston; and a main seal coupled to the valve piston for sealing the cylinder assembly from supply pressure while pressure is ported to the valve piston by the inner cap for holding the piston assembly in the non-actuated position, the main seal sealing pressure ported to the valve piston by the inner cap from supply pressure ported to the piston assembly, wherein the head valve assembly ports supply pressure to the piston assembly for actuating the piston assembly for driving the fastener. 13. The pneumatic fastener as claimed in claim 12, wherein the inner cap further comprises an exhaust port for parting exhaust from the head valve assembly. 14. The pneumatic fastener as claimed in claim 12, wherein the inner cap is fanned of a lubricious plastic. 15. The pneumatic fastener as claimed in claim 12, wherein the main seal comprises a lip seal for forming a seal with the inner cap. 16. The pneumatic fastener as claimed in claim 12, further comprising a snap-lock mechanism for coupling the main seal to the piston valve. 17. The pneumatic fastener as claimed in claim 16, wherein the snap-lock assembly comprises a plurality of legs extending from the main seal and a plurality of leg receivers disposed in an inner surface of the valve piston, each of the plurality of legs being received in a corresponding one of the plurality of leg receivers for coupling the main seal to the valve piston. 18. The pneumatic fastener as claimed in claim 17, wherein the piston assembly includes a projection, the plurality of legs for receiving and retaining the projection upon return of the piston assembly from the actuated position to the non-actuated position. 19. The pneumatic fastener as claimed in claim 17, further comprising a compression spring for biasing the valve piston toward the piston assembly and causing the main seal to seal the cylinder assembly from supply pressure, the compression spring traps the plurality of legs for preventing the main seal from separating from the piston valve by the piston assembly as the piston assembly moves from the non-actuated position to the actuated position. 20. The pneumatic fastener of claim 12, further comprising a handle coupled to the housing, wherein the handle comprises an outlet passageway for exhausting air from the head valve assembly. 21. The pneumatic fastener of claim 20, wherein an end of the handle opposite the housing includes an outlet port in communication with the outlet passageway. 22. The pneumatic fastener of claim 20, wherein the handle further comprises an inlet passageway for delivering compressed air to the head valve assembly. 23. The pneumatic fastener of claim 20, wherein the inner cap further comprises an outlet port for delivering gas from the head valve assembly to the outlet passageway. 24. A head valve assembly for a pneumatic fastener including a piston assembly reciprocated within a cylinder assembly for driving a fastener and a housing having an end cap for at least partially enclosing the head valve assembly, the head valve assembly comprising: means for porting supply pressure to the piston assembly for moving the piston assembly within the cylinder assembly from a non-actuated position to an actuated position for driving the fastener; means, disposed at least partially within the end cap and around the supply pressure porting means, for porting pressure to the supply pressure porting means; and means, coupled to the supply pressure porting means, for sealing the cylinder assembly from supply pressure for holding the piston assembly in the non-actuated position, wherein the sealing means seals pressure ported to the supply pressure porting means from supply pressure ported to the piston assembly. 25. A pneumatic fastener, comprising: a housing; a trigger and a trigger valve coupled to the housing for actuation of the pneumatic fastner; a fastener driving assembly disposed within the housing, the fastener driving assembly including a cylinder and a piston that reciprocates within the cylinder to drive a fastener; a head valve coupled to the fastener driving assembly, wherein actuation of the head valve causes compressed air to drive the piston within the cylinder to drive the fastener; an end cap coupled to the housing; and an inner cap disposed at least partially within the end cap, the inner cap including an inlet port for delivering the compressed air from an external compressed air source to the head valve. 26. The pneumatic fastener of claim 25, wherein the inner cap further comprises an exhaust port for porting exhaust from the fastener driving assembly. 27. The pneumatic fastener of claim 26, further comprising a handle coupled to the housing, wherein the handle comprises an outlet passageway for exhausting air from the exhaust port. 28. The pneumatic fastener of claim 27, wherein an end of the handle opposite the housing includes an outlet port in communication with the outlet passageway. 29. The pneumatic fastener of claim 27, wherein the handle further comprises an inlet passageway for delivering compressed air to the inlet port. 30. The pneumatic fastener of claim 25, wherein the inner cap comprises plastic. 31. The pneumatic fastener of claim 25, further comprising a seal coupled to the valve for sealing the fastener driving assembly from supply pressure while pressure is ported to the piston by the inner cap. 32. A head valve assembly for a pneumatic fastener including a fastener driving assembly disposed within a housing, the fastener driving assembly including a cylinder and a piston that reciprocates within the cylinder to drive a fastener, the head valve assembly comprising: a valve piston coupled to the fastener driving assembly, wherein actuation of the valve piston causes compressed air to drive the piston within the cylinder to drive the fastener; and a single unitary sealing member coupled to the valve piston between the valve piston and the fastener driving assembly, the sealing member configured to seal the cylinder from supply pressure while pressure is ported to the valve piston. 33. The head valve assembly of claim 32, further comprising a snap-lock mechanism for coupling the sealing member to the piston valve. 34. The head valve assembly of claim 33, wherein the snap-lock assembly comprises a plurality of legs extending from the sealing member and a plurality of leg receivers disposed in an inner surface of the valve piston, each of the plurality of leg being received in a corresponding one of the plurality of leg receivers for coupling the main seal to the valve piston. 35. The head valve assembly of claim 34, wherein the piston assembly includes a projection, the plurality of legs for receiving and retaining the projection upon return of the piston assembly from the actuated position to the non-actuated position.