(under subclass 19) Valves, which operate as a direct result of a pressure change in the fluid normally filling the distributing pipes or an auxiliary system of pipes extended into the area to be protected. These valves are used principally in dry pipe distributing systems and usually include a "water-valve", which is held closed against the pressure of the source by force transmitted from an "air-valve" exposed to the pressure of the fluid normally filling the distributing-pipes.
