Expanding gate valve with pneumatic actuator

An actuator device for actuation of a gate valve of the expanding gate type which comprises a valve body with a valve chamber therein and a flow passage extending through said valve body and communicating with said valve chamber, an expandable gate assembly mounted within said valve chamber for movement in a collapsed condition between open and closed positions with respect to said flow passage, said gate assembly including a gate element and a segment which are expanded away from each other at said open and closed positions and are provided with ports which are aligned with one another and the flow passage in said open position, said gate element and segment being each provided with an outer sealing surface for sealing against valve seats provided in said valve body at opposite sides of the gate assembly when the gate assembly is expanded in the open and closed positions, said valve body having a bore extending form the exterior of the valve body into said valve chamber in generally transverse relation to said flow passage;

• pneumatic powered actuator means for moving the gate assembly transversely with respect to said flow passage said open and closed positions, said actuator means comprising an actuator housing mounted on said valve body and defining a first piston chamber therewith;
• a primary piston slidably mounted in said first piston chamber;
• fluid inlet means provided through the wall of said housing and adapted for connection to a source of pneumatic pressure whereby pressurized fluid may be selectively admitted to said first piston chamber on a fluid receiving side of said primary piston;
• means including one side of said primary piston for defining a second piston chamber;
• a drive piston slidably received in said second piston chamber;
• and actuator stem connected at one end to said drive piston and at its other end to the gate assembly, said drive piston being movable with the actuator stem in the axial direction of the stem to move the gate assembly transversely with respect to said flow passage between said open and closed positions;
• spring means in said actuator housing for continuously urging said drive piston to an abutting relationship with said primary piston and in a direction opposed to the pneumatic pressure applied to said primary piston, said primary piston being provided with a flow control orifice extending through the primary piston whereby pressurized pneumatic fluid admitted to said first piston chamber will be communicated to said drive piston through said flow control orifice;
• and stop means for limiting the length of the primary piston stroke to a lesser length than that of the drive piston stroke when pressurized pneumatic actuating fluid is admitted to said first piston chamber, said orifice acting to restrict the flow of pneumatic actuating fluid into said second piston chamber after termination of the primary piston stroke and thereby control the velocity and momentum of said drive piston, actuator stem, and gate assembly in the operation of the gate valve by maintaining the velocity substantially constant.