Patent ID: 8714515

Claim:
A sliding stem valve assembly comprising: a control valve having a fluid inlet and a fluid outlet, the control valve comprising a valve plug that is movably positioned between the fluid inlet and the fluid outlet to control fluid flow through the control valve, the valve plug being connected to a control valve stem; an actuator for moving the valve plug, the actuator comprising an actuator housing and a diaphragm mounted within the actuator housing, the diaphragm dividing the actuator housing into at least two chambers, an actuator stem being operatively coupled to the diaphragm at one end and moving in a reciprocating manner in response to movement of the diaphragm, the actuator stem being connected to the control valve stem at another end; and a hydraulic sleeve mounted between the control valve and the actuator housing, the hydraulic sleeve being connected to one of the control valve stem and the actuator stem, the hydraulic sleeve moving either the control valve stem or the actuator stem in response to varying hydraulic pressure within the hydraulic sleeve, wherein the hydraulic sleeve includes a sleeve housing and a hydraulic piston, the sleeve housing having an interior volume defined between a longitudinal inner surface of an outer wall and a longitudinal outer surface of an inner wall, the control valve stem being slidably disposed within a longitudinal opening defined by a longitudinal inner surface of the inner wall, wherein an inner surface of the hydraulic piston is adjacent to the outer surface of the inner wall of the sleeve housing, and wherein a first end of the hydraulic piston is slidably disposed within the interior volume of the sleeve housing and a second end of the hydraulic piston is slidably disposed outside of the interior volume of the sleeve housing; wherein the hydraulic piston is an elongated hollow cylinder having a flange portion at the first end, the flange portion sealingly engaging the inner surface of the outer wall to divide the interior volume into a low pressure chamber and a high pressure chamber, wherein pressure changes in the low pressure chamber and the high pressure chamber cause the hydraulic piston to displace within the sleeve housing.