Temperature responsive bypass valve

Claim 1

For use in a fluid circuit embodying fluid guide structure defining a pair of distinct fluid paths and a bypass passage interconnecting said paths and having a valve set therein, an improved thermally responsive valve subassembly comprising: (a) a valve member; (b) means mounting said valve member in one of said paths for movement toward and away from seating engagement with said valve seat; (c) means resiliently biasing said valve member away from said valve seat; (d) thermally responsive means disposed in said one path and connected to said valve member to overcome said biasing means and thereby move said valve member to engage said valve seat when the fluid temperature in said one path exceeds a predetermined magnitude; (e) means responsive to pressure of the fluid at the face of said valve member for normally exerting a force on said valve member counterbalancing the effect of fluid pressure acting on the face of said valve member; and (f) means for disabling said counterbalancing force exerting means when the fluid pressure at the face of said valve member exceeds a predetermined limit, wherein said counterbalancing force exerting means includes a piston chamber, a piston in said chamber, a normally closed spring biased check valve means mounted on said piston, means communicating the fluid pressure at said valve member face to said piston chamber, and a relief passage at the downstream side of said check valve means whereby the check valve means will open and relieve the pressure in said piston chamber when the pressure therein is excessive.