Patent ID: 8066197

Claim:
A thermal bypass valve for a heat exchanger circuit, comprising: a valve housing forming a valve chamber including a bypass passage and having a first port for flow of a heat exchange fluid into said valve chamber, a second port for flow of said heat exchange fluid out of said valve chamber, a third port for flow of said heat exchange fluid from said valve chamber to a heat exchanger, a fourth port for flow of said heat exchange fluid from said heat exchanger to said valve chamber, and a bypass port defined by a valve seat provided in said housing; axially aligned first and second thermally sensitive actuators mounted in said chamber, connected to one another, and having respective first and second actuator bodies and respective first and second movable pistons, each extendible from one end of its respective actuator body, at least one of said actuator bodies being normally movable in the valve chamber in response to extension of its piston, one of said actuators being adapted to extend its piston at a selected higher temperature than a predetermined temperature required for the other actuator to extend its respective piston; a valve member mounted on one of said first and second actuators which is adjacent said valve seat and movable by either the first or the second actuator from a first position, where said bypass port is in an open state, to a closed position where said bypass port is closed by said valve member engaging said valve seat; and a return spring mechanism mounted in said housing and adapted to bias an adjacent one of said actuators away from the valve seat, wherein the bias of the return spring mechanism can be overcome during use of the bypass valve by extension of either said first piston or said second piston depending on the temperature to which the actuator bodies are heated.