apparatus for controllably transferring fluid from a pierceable pressurized container includes a valve body , a stem member which is threadably connected to the valve body at one end and a fluid - conducting hose at the other end , and an elastomeric valve ball disposed in a cavity between the body and the stem member . the valve ball controls fluid flow from the container through the valve body and stem member to the hose in response to rotation of the valve stem relative to the body . simultaneously , the valve balls acts as a check valve to prevent flow of fluid to the container . an o - ring seal between the stem and the valve body is adapted to leak at high pressure and bleed off fluid .