Abstract: A valve for use in a pressure differentially operated servo-motor to regulate the flow of fluid through a bore in a hub from first and second sources in response to movement of an input member by an operator. The valve has a resilient disc member with a peripheral surface and a central opening. First and second annular ribs symmetrically extend from opposite sides of the disc adjacent the central opening. A spring connected to the input member holds the peripheral surface in sealing engagement with the hub. In a first mode of operation, the spring holds the input member against the first annular rib to allow the fluid from the first source to freely communicate between first and second passages in the hub by way of the bore.