Patent ID: 7367785

Claim:
A valve assembly for a gas-driven motor comprising: a shiftable valve for alternatively supplying a motive gas through first and second supply ports to opposed first and second power pistons in opposed motive gas chambers, respectively, and for effecting alternating exhaust of said chambers; the shiftable valve having a longitudinal axis and a front face with a valve projection located thereon, and a rear face with a valve projection located thereon, the valve projections being coaxially aligned along the longitudinal axis; a valve block having a chamber with a front end and a rear end disposed around the shiftable valve and permitting axial movement of the shiftable valve along its longitudinal axis, wherein the front face of the shiftable valve is located in the front end of the chamber and the rear face of the shiftable valve is in the rear end of the chamber; the valve block further comprising inner exhaust passages in fluid communication with the front and rear ends of the chamber, outer exhaust passages corresponding to and in fluid communication with each of the inner exhaust passages, and constricted regions between the inner and outer exhaust passages, the constricted regions configured to define valve seats into which the valve projections mate, such that upon reciprocating movement of the shiftable valve along the longitudinal axis, the inner exhaust passageways are alternately opened to their corresponding outer exhaust passageways.