Pilot controlled check valve

摘要

A cartridge for an unlockable check valve for a mining support frame ram has a two part cartridge housing 72, 72 coupled by a thread 75. Hollow valve piston 78 having a fluid port A and radial apertures 52 in the housing is spring 84 biased in a closing direction such that a flange 56 engages seat 58 in the housing to separate the fluid port from a load port 54. The valve piston engages within a control piston 76 with a sliding fit. The control piston slides within a bore 60 supplied with control fluid through a port 50 which is spaced from the bore closed end. The circumference of the piston is recessed to provide an annular or ring gap 64 in the port region to provide damping. A circuit is also provided (Fig. 2) in which two such check valves communicate with a ram head end inlet, one (A) connecting to a valve block (A) and the other (R) to tank (R). Control fluid is supplied from a ram rod end line (B).