Abstract: Pressurized fluid circuits are provided which are suitable for use in a pressure drop detector for a pressurized fluid fire alarm system. The pressurized fluid circuits are provided as channels in the surface of a block of material and include one channel connected to a source of fluid pressure. The channels are associated with valve regions by means of which, with a diaphragm pressed thereagainst, a required one or more of the channels can be closed off.In its application to a pressure drop detector a normally pressurized region of the diaphragm may support a mechanical linkage of the detector such that if the pressure drops, on release of pressure in the system, the collapsing of the diaphragm allows the mechanical linkage to be released thus actuating a fire alarm.

Abstract: Pressure drop detectors are provided which are suitable for use in pressurized fluid fire alarm systems. The pressure drop detectors have pressurized fluid circuits provided as channels in the surface of a block of material, including one channel connected to a source of fluid pressure. The channels are associated with valve regions by means of which, with a first diaphragm pressed thereagainst, a required one or more of the channels can be closed off.The pressure drop detectors have a normally pressurized region of the first diaphragm which by means of a first piston normally supports a mechanical linkage of the detector. If the pressure drops however on release of pressure in the circuit connected to the detector, the collapsing of the first diaphragm allows the mechanical linkage to be released thus actuating a fire alarm.