Quick acting valves

DETAILED DESCRIPTION I claim: 1.
A quick acting isolating valve comprising in combination a valve body having a fixed seat defining an opening through which connected system fluid may flow in a path between an inlet and an outlet, a moveable head adapted to cooperate with said seat to open and close said opening to fluid flow, said head being carried on a stem which is provided with a piston reciprocable in a piston chamber formed in the valve body substantially isolated from the fluid flow path, means operatively effective for applying system pressure to both sides of said piston, auxiliary valve means selectively operable between a first position for retaining system fluid pressure at the underside of said piston and a second position relieving system fluid pressure from the underside of said piston to enable movement of said head toward said seat, a fluid outlet from the chamber communicating the underside of said piston with said auxiliary valve means and effective when said auxiliary valve means is in said second position to permit discharge of system fluid from the chamber upon movement of the piston within the chamber as the moveable head moves toward said seat and means for effecting progressive restriction of fluid flow through the outlet to cushion movement of said head as the moveable head approaches the position of abutment with said seat.
2.
A valve according to claim 1 wherein the means for effecting progressive restriction of fluid flow from the piston chamber comprises at least one fixed orifice in the chamber progressively restricted in aperture by the movement of the piston and stem.
3.
A valve according to claim 2 wherein one or more fixed orifices are provided in an end wall of the chamber, and the piston stem provides the means for restricting in aperture each of said orifices.
4.
A valve according to claim 3 wherein a fixed orifice is formed in the end wall of the chamber as the mouth of a sleeve in which the stem of the piston reciprocally moves and the stem is of variable cross section over the portion which co-acts with the mouth of the sleeve so that the cross-sectional area of the aperture between the stem and the mouth of the sleeve varies as the stem moves in the sleeve