Abstract: A bypass system has a source of a fluid to be cooled and a heat exchanger for selectively cooling the fluid. A bypass valve is mounted on a line to selectively bypass the fluid prior to reaching the heat exchanger. The bypass valve includes a valve poppet, a valve seat, a piston, a valve housing and a wax portion. A piston is moveable along an axis and allows movement of the valve poppet toward and away from the valve seat. The piston moves within a valve housing. A wax portion expands as a temperature increases, and causes the valve poppet to move against the valve seat. The wax portion cools if the temperature lowers such that the valve poppet moves away from the valve seat. There is a sealing surface on the valve poppet in sealing contact with the valve seat. The sealing surface is part-circular in a plane in which the axis lies. A bypass valve is also disclosed.

Abstract: A novel digital servo valve system for use in controlling a displaceable actuator includes a valve body with ports, a valve spool displaceable within the valve body to regulate fluid flow through the ports, and a motor having a drive shaft which displaces the valve spool. The system is characterized by a null adjustment mechanism which makes a null rotational position of the drive shaft coincide with a null position of the valve spool, at which positions the valve spool cuts off fluid flow through the ports. The null adjustment mechanism provided in accordance with the present invention permits the null positions of the valve spool and stepper motor to be adjusted without having to disassemble the servo valve.