Patent ID: 7284475

Claim:
Reciprocating pneumatic drive apparatus for use in association with a compressed gas system having an area of higher pressure and an area of lower pressure, said apparatus comprising: (a) a cylinder having a cylindrical sidewall extending between a pair of cylinder heads, each of which has a piston rod opening; (b) a piston having first and second piston faces plus first and second piston rods, each projecting from a corresponding piston face, said piston being reciprocatingly slidable within the cylinder, with each piston rod being sealingly slidable through the piston rod opening of a corresponding one of the cylinder heads, said piston demarcating first and second variable-length cylinder chambers, one at each end of the cylinder; (c) a pair of spaced-apart piston seals disposed circumferentially around the piston, for sealing between the piston and the sidewall, said piston seals defining the ends of an annular space; (d) valve means operable between a first position in which the first and second cylinder chambers are in fluid communication with the areas of higher and lower pressure respectively, and a second position in which the first and second cylinder chambers are in fluid communication with the areas of lower and higher pressure respectively, so as to induce reciprocating movement of the piston within the cylinder; and (e) switch means operable to switch the position of the gas flow valve at or near the end of each stroke of the piston; wherein: (f) the piston has a transverse passage extending between the piston faces, and a radial passage extending between the transverse passage and the annular space; and (g) the apparatus further comprises shuttle valve means retainingly disposed within the transverse passage, for enabling gas from whichever cylinder chamber is under lower pressure to flow through the transverse and radial passages into the annular space, while preventing the flow of gas from the cylinder chamber under higher pressure into the transverse passage.