The body has a fluid inlet port for receiving pressurized fluid and a fluid outlet port connected to the retention balloon. A first passage connects the fluid inlet port and the fluid outlet port, A second passage in the body is connected to the balloon fluid return path and is at the pressure of the retention balloon. A. valve prevents fluid flow through the first passage when actuated. The valve includes a pressure-responsive member movable to a position to obstruct fluid flow in response to fluid pressure in the second passage exceeding the predetermined level. Flexible means such as a membrane defines a normally open portion of the first fluid passage, which is closed by the moveable means bearing on the membrane when pressure exceeding the predetermined level actuates the valve.
