Control valve means for hydraulic press

Claim 1

In a hydraulic press: a main ram cylinder, a main ram in said main ram cylinder and extendable to and retractable From a clamping position, said main ram having a rearwardly directed surface against which fluid pressure may act to extend said ram to its clamping position and a forwardly directed surface against which fluid pressure may act to retract said ram, a booster ram cylinder in said main ram, a hollow booster ram having a front end portion extending into said booster ram cylinder, stationary support means connected to a rear end portion of said booster ram and having a first chamber therein communicating with the interior of said booster ram, a source of prefill fluid, a control valve body disposed in surrounding relationship to said booster ram in the zone between said main ram cylinder and said support means and having a fluid passage for communicating said source of prefill fluid with the interior of said main ram cylinder behind said main ram, a prefill valve piston within said control valve body disposed in surrounding relationship to said booster ram and being movable between a first position in which said fluid passage is open and a second position in which said fluid passage is closed off to block the flow of prefill fluid between said main ram cylinder and said source of prefill fluid, said stationary support means further including a generally cylindrical prefill pin chamber communicating intermediate the ends thereof with said first chamber in said stationary support means, communicating at its rear end with a pilot pressure port and communicating at its front end with the interior of said control valve body at a location in alignment with the path of movement of said prefill valve piston, a one piece cylindrical prefill valve pin movably disposed in said chamber and comprising a pilot pressure reaction surface at the rear end thereof, a surface at the front end thereof for engaging said prefill valve piston to urge the prefill valve piston toward its closed second position, and a circumferentially grooved portion in the periphery of said cylindrical pin intermediate the ends thereof of such length as to remain in communication with said first chamber in said stationary means throughout the range of movement of said prefill valve pin and to communicate with the space behind said prefill valve piston when the prefill valve pin reaches its forwardmost position, a source of pressurized pilot fluid and means for applying said pilot fluid to said pilot pressure reaction surface, means defining a fluid passage from said space behind said prefill valve piston to the interior of the rear end portion of said main ram cylinder when said prefill valve piston is in its said second position, pressurized fluid source means, a first multiposition valve external to said main and booster ram cylinders and being connected to said pressurized fluid source means, conduit means operably connected to said first multiposition valve for directing pressurized fluid to said first chamber in said support means in a first position of said first multiposition valve and for directing pressurized fluid to the interior of said main ram cylinder ahead of said forwardly directed surface of said main ram in a second position of said first multiposition valve, and means, including a second multiposition valve external to said main and booster ram cylinders and having a position it assumes just prior to actuation of said first multiposition valve to the said second position of said first multiposition valve, for communicating said space behind said prefill valve piston with said source of prefill fluid to relieve the pressure behind said main ram prior to application to said main ram of fluid pressure in a direction to retract said main ram.