Pressure relief valve for hydraulic pip-prop - has gas spring to hold valve piston on its seat

摘要

The hydraulic pit prop is fitted with a valve to relieve excessive hydraulic pressure in the event of a rock slip imposing an excessive load on the pit prop. The working length of the pit prop is thus reduced with a simultaneous reduction in load so preventing damage to the pit prop. The valve has a cylindrical body (1) with an axial inlet (4) and a number of radial outlets. The body houses a piston (6), which, together with the body and the end cap (12) forms a gas spring. The upper end of the piston has a sealing ring (9) which co-operates with a valve seat formed in the body. The tip (29) of the piston (6) is conical with a concave surface which facilitates the radial outflow of the hydraulic fluid.