Centrifugal hydraulic head relief valve

A hydraulic clutch having a centrifugal head relief valve comprising, a friction clutch including a plurality of rotating friction disks forming a disk stack, a hydraulic actuator defining a hydraulic fluid pressurizing chamber for engaging said friction disks of said disk stack, a relief valve in communication with said pressurizing chamber, said relief valve including an annular clutch drum defining a radial valve supporting opening and a vent passage, relief passage means connecting said pressurizing chamber with said valve, a valve aligning means concentrically mounted in said valve supporting opening providing connecting passage means and a vent opening between said vent passage and said relief passage means, a movable valve element reciprocally mounted in said valve supporting opening slidably engaging said valve aligning means and defining an expansible fluid pressure chamber, a valve cover removably retaining said valve aligning means concentrically within said opening, resilient means normally biasing said movable valve element radially outward, a central opening communicating with said connecting passage means in the outer end of said valve aligning means for admitting pressurized fluid to said expansible fluid pressure chamber to bias said movable valve element radially inwardly of said clutch drum to close said relief valve when fluid is pressurized in said pressurizing chamber and the clutch is engaged, said valve aligning means defining said vent opening extending to communicate with said vent passage in said clutch drum for release of fluid from said pressurizing chamber when said clutch is released.