Closing assist for valves

Claim 1

A shut-off valve for use in a line carrying steam under pressure comprising: a valve body; an inlet in said valve body; an outlet in said valve body; a circular main valve seat between said inlet and said outlet; a cylindrical section in said valve body coaxial with and spaced from said valve seat; a closure member slidably engaged in said cylindrical section on the upstream side of said valve seat, said closure member engaging said main valve seat when said shut-off valve is in closed position; a valve stem connected with said closure member and extending through said valve body to the exterior thereof; spring means urging said stem and said closure member toward said valve seat; a power cylinder rigidly connected to said valve body above said body said power cylinder being concentric with said cylindrical section; a power piston slidably mounted within said power cylinder; a piston rod connected to said piston and extending downward from said piston and through said power cylinder, said piston rod being connected at its bottom to said stem; a control cylinder, rigidly connected with said power cylinder, intermediate said power cylinder and said valve body; a pilot valve port extending downward through said closure member; a pilot valve seat on the upper end of said pilot passage; a pilot valve at the lower end of said stem, said closure member being connected to said stem for limited sliding movement, said pilot valve engaging said pilot valve seat when said stem is displaced to the limit of its movement relative to said closure member in the direction of said pilot passage, said pilot valve being disengaged from said pilot valve seat when said stem is displaced to the limit of its movement relative to said closure member in the direction away from said pilot valve port; a control piston slidably mounted within said control cylinder and connected to said piston rod; a first oil line connected to said control cylinder above said control piston; an air-oil booster connected with said first oil line; a second oil line connected to said control cylinder below said control piston; an oil valve connected between said first oil line and said second oil line so that when said oil valve is closed oil will flow only through said first oil line; an air-oil booster connected with said first oil line; a first air line carrying air under pressure, said first air line being connected to said air-oil booster; whereby air pressure in said power-cylinder below said power piston can be released so that said spring means will move said valve stem and said closure member toward said valve seat with said control cylinder regulates the speed at which said shut-off valve can be closed, actuation of said air valve will allow air from said first air line to act on said air-oil booster so that oil in said first oil line and in said control cylinder above said control piston will be pressurized to urge said control piston and said closure member toward said seat to close said valve and to prevent fluid flow between said inlet and said outlet.