Abstract: A gate valve provides an efficient and effective seal from high pressures to pressure differentials below 50 psi through a self-aligning gate of reduced mass (semi-gate). The invention provides a transmission between the gate and stem which permits its sealing surface to remain normal to the relative surface of the seat irrespective of pressure, circulation rate, or flow medium (gas or liquid). This is accomplished through the full floating nut element which, when loosely engaged to the stem and inserted into an oversized slot at the upper end of the semi-gate, allows the gate to move axially in the direction of flow without interfering with the vertical movement of the gate by the stem. This feature is accomplished by introducing a clearance between the stem and nut. The gate is of reduced mass to allow a more instantaneous response to pressure transients because of its lighter weight and reduced profile.

Abstract: A single acting pump has a piston with an elastomeric and synthetic fabric seal ring and is provided with means to supply fluid to the piston and passages in the piston for circulating fluid to cool and clean the piston on both the pressure stroke and the back stroke. The passages in the piston include a check valve preventing flow of fluid to the back side of the piston during the pressure stroke and permitting fluid flow to the seal ring during the back stroke.