Abstract: A hydraulic servo valve assembly and a control system therefor employing a pneumatic sensor-actuator are disclosed. The servo valve assembly comprises a servo-operated power valve assembly including a differential piston, a solenoid operated override and hysteresis adjustment. The valve assembly is a "snap-action" device wherein the power valve differential piston is selectively positioned through use of the pneumatic sensor controlled servo valve to vent the pressure applied to the larger area reaction surface of the piston.

Abstract: A valve construction having a housing provided with an inlet and an outlet and a movable valve seat disposed between the inlet and the outlet. A movable valve member is provided for opening and closing the valve seat. A condition responsive unit is operatively associated with the valve member to move the valve member relative to the valve seat in response to the conditions sensed by the condition responsive unit. A snap opening unit is interconnected to the valve seat to rapidly move the valve seat away from the valve member when the valve member has initially opened the valve seat a certain amount.

Abstract: A valve body includes a base section having an inlet and an outlet and means forming a valve seat therebetween. A flexible diaphragm is supported for movement relative to the valve seat and includes a center by-pass port which is opened and closed by a valve member supported for axial movement by a closure section of the valve body. A pin-like actuating lever is pivotally supported by a flexible seal secured to the closure section and has an inner end portion projecting into an opening formed within the valve member. An elongated U-shaped bimetallic actuating element is mounted on the closure section generally parallel to the lever and includes a movable head portion. The bimetallic actuating element is preferably connected as a resistance in series with an electrical load, and a spring is compressed against the outer end of the actuating lever to cause rapid snap-action movement of the lever, and the valve member in response to slower movement of the head portion of the actuating element.