Abstract: In one embodiment, a valve body contains a flexible valve sleeve between a fluid inlet and a fluid outlet, and an annular chamber around the sleeve connects with the inlet so that fluid pressure in the chamber normally compresses the sleeve to a closed position. A manually operated pilot valve reduces pressure in the chamber so that the sleeve is expanded by fluid pressure from the inlet to open the valve.In another embodiment, a valve body contains a flexible diaphragm which normally closes an inlet valve port and defines a pressure chamber isolated from a fluid outlet. A manually operated pilot valve reduces pressure in the chamber so that the diaphragm is unseated from the inlet port by fluid pressure from the inlet to open the valve.