PRESSURE RELIEF VALVE, PRESENTLY FOR HYDRAULIC REMOVAL ELEMENTS OF UNDERGROUND PIT OPERATION

摘要

An excess pressure valve particularly for props having telescopic parts which are extensible or retractable by fluid under pressure used in underground mining operations, comprises a valve housing having a bore therethrough with a connection end connectable to the fluid under pressure and an opposite opened end. A tubular sleeve is slidable in the bore and has a passage therethrough for the fluid under pressure and it has an annular inlet end face facing the connection end and an opposite annular pressure end face which opposes a piston which is also slidable in the bore between the sleeve and the opened end. The fluid under pressure maintains the sleeve and the piston in slightly spaced relationship so that there is a small space therebetween which is sealed by an annular pressure seal. When the fluid under pressure reaches a predetermined pressure the space moves beyond the seal and communicates with a discharge relieving bore and when it moves beyond this initial position it communicates with a larger bore permitting the discharge of the fluid under pressure from the valve. The construction advantageously includes a spring plate which is biased by a spring against the piston to urge it to the connection end. An additional spring is employed to bias the sleeve in a direction toward the piston. The spring plate is advantageously interposed between a coil spring and the piston and this spring plate carries a rod member which forms a load indicating device which projects out the open end when the pressure increases to indicate by indications on the rod the amount of pressure in the fluid pressure system.