Priority hydraulic control valve

Claim 1

An open-center valve section which establishes priority flow in the adjacent upstream section in a series of connected open-center valves utilized in a stack, the valve section having a body provided with a bore and a valve element slidable therein defining an open-center flow passage connecting a fluid pressure source to reservoir through the other sections in the stack; a motor passage; a return passage connected to reservoir; a blind-ended power passage connecting the fluid pressure source to said bore; the valve element having a first position with flow to the motor passage blocked and the open-center passage open, allowing fluid from the pressure source to pass to reservoir and second position blocking flow in the open-center passage and allowing flow from the power passage to the motor passage, the improvement comprising: a load check valve means positioned in the power passage normally springbiasing the power passage closed; and servo means having a piston and connecting chamber separate from said power passage operating the load check valve responsive to pressure in the open-center passage opening the power passage only when sufficient pressure exists in the open-center passage.