Patent ID: 7278561

Claim:
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.