DISPOSITIF DE MANOEUVRE DE SOUPAPE

摘要

A seepage-resistant valve system employing a pressure operated valve operator. A selectively operated valve position control system may apply gas to a piston in a cylinder associated with a housing to move the same to control valve position. The housing is in fluid communication with the cylinder and a back pressure valve is employed so that a positive gas pressure is maintained in both the cylinder and the housing regardless of the position of piston within the cylinder to preclude seepage of ground water into the valve operator.