The Viking Explosion-Proof/Watertight Pressure Supervisory Switches are for use in areas exposed to weather or explosive atmospheres. The switches are designed to actuate an electric alarm at either a predetermined low-pressure setting or a predetermined high-pressure setting on any system pressurized with air, nitrogen, or water. These systems include dry-pipe systems, preaction systems, pneumatic release lines, foam/water sprinkler systems, and any other system pressurized with air or nitrogen, as well as pressure tanks and waterflow control systems. The switch may also initiate signals to release control panels, annunciator panels, or any other auxiliary equipment that can be controlled by the opening or closing of an electrical switch.