A valve for a plumbing system has a housing with an inlet and an outlet and a valve body movable in the housing between a throttle position with a decreased a flow cross section and reduced flow between the inlet and outlet and an open position with a large flow cross section and free flow between the inlet and outlet. Structure in the valve body applies hydraulic pressure from the inlet or outlet to the valve body to shift same into the throttle position when a pressure differential between the inlet and the outlet exceeds a specified value and into the open position in the absence of a pressure differential between the inlet and the outlet.
