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.主體具有用於接納加壓流體之一流體入口埠及連接至壓力氣囊之一流體出口埠。一第一通路連接該流體入口埠與該流體出口埠。該主體中之一第二通路連接至氣囊流體返回路徑且處於壓力氣囊之壓力處。當被致動時，一閥防止流體流動穿過該第一通路。該閥包括回應於該第二通路中之流體壓力超過預定位準而可移動至一位置以阻斷流體流動之一壓力回應部件。諸如一薄膜之撓性構件界定該第一流體通路之一正常係打開之部分，當超過該預定位準之壓力致動該閥時該正常係打開之部分由承靠在該薄膜上之可移動構件關閉。
