Abstract: A deformable seal element is installed in a seal groove to thereby form a completed seal between static components being the housing of a rockdrill and an insert in the housing. The seal element is deformed to assume the shape of the seal groove. A rib in the seal groove digs into the seal element, whereby axial movement or dither of the seal element in the seal groove is restrained.

Abstract: Disclosed is a device for converting pressure fluid input of one fluid to pressure fluid output of a second fluid without contaminating either fluid. The transformation is accomplished by a unique H section piston which cooperates the internally protruding endcaps enclosed in a double ended cylinder; the piston having a central control valve which reverses the piston on control pin end of stroke contact. Positive reverse action is obtained by means of endcap plungers which operate in response to piston position and pressure of the one fluid. The device is double acting and is enclosed totally within a single cylindrical module which is compact and inexpensive to manufacture.