Valve mounted changeover switches provide position status via a robust volt free changeover switch, rated to 230V 10 amps, allowing direct switching of pumps or relays upon valve actuation or 0.75 amp rated nonmercury normally open switches.
Single phase mercury switch assemblies house one single pole changeover switch, whilst three phase installations have three SPCO switches, housed within one enclosure.
The SPCO switch is a steel encased mercury switch, potted within a dielectric resin and encapsulated within a sealed terminal enclosure, which in turn, is fixed within a grey ABS valve mounted housing. The switching action is generated by valve closure. As the valve lever travels from 45 degrees above the horizontal plane of the pipe to 45 degrees below the pipe, although both single and three phase versions can also be used with vertically mounted Free Fall Fire Valves.