Abstract: A cartridge type sleeve and plunger hydraulic valve is retained in a blind bore along with a biasing spring by a closure plug. Spaced transverse passages intersecting the bore are either separated or connected depending upon whether the plunger is either shifted by the spring bias or by fluid pressure overcoming the spring bias. An elastomeric seal eliminates leakage when the valve is in closed position. To insure against accidental fall out of any loose parts when the valve is disassembled under difficult working conditions, as in mines, O-rings are utilized as retainers for the spring and other parts.

Abstract: A valve, the housing and gate of which are composed of molded rigid polyvinylchloride, the valve body having an interior chamber with a main upstream inlet and a main downstream outlet and an annular valve seat in the housing, and a gate being arranged in the housing which is spring-biased to a normally closed position with an O-ring in sealing relation on the seat to effectively block fluid flow through the valve and said spring being selected so as to have a resiliency to yield in response to predetermined upstream fluid pressure to unseat the valve member and permit flow of fluid through the valve so long as the predetermined pressure is exceeded.