Prefill valve for hydraulic clamping devices

Claim 1

In a fluid-operated press having a relatively small diameter piston to provide rapid movement of a ram member to a predetermined position and a relatively large diameter piston to provide a large force, a valve member including an end wall and a valve body attached thereto, said valve member having at least a pair of fluid inlets and a pair of fluid outlets, each of said fluid outlets being adapted to communicate with one of said pistons, one of said fluid inlets being in communication with a source of relatively low-pressure fluid and the other of said fluid inlets being in communication with a source of relatively high-pressure fluid, a generally annular closure member slidably positioned within said valve body in fluidtight relationship therewith and incorporating a double-acting piston adapted to selectively open or close said low-pressure fluid inlet between said source of relatively low-pressure fluid and one of said actuating pistons, said closure member being biased to a position to permit flow from said low-pressure source and said actuating piston, the improvement comprising: a. at least one auxiliary piston slidably positioned in said end wall in abutting relationship with an end of said annular closure member, said piston having closed end faces and an internal bore including at least a pair of spaced radial passageways extending through the sidewall of said piston; b. means for providing communication between said source of high-pressure fluid and one of said end faces of said auxiliary piston; c. means for providing communication between said source of high-pressure fluid and said bore of said auxiliary piston through one of said radial passageways in said auxiliary piston; d. wherein said annular closure member provides communication between the head of said double-acting piston and the opposite face of said closure member.