Murphy 4-1/2 inch (114 mm) diameter dial pressure Switchgauge instruments accurately and reliably measure and indicate pressures in applications such as gas compressors control panels, pumping applications, industrial process applications, etc. The Switchgauge versions incorporate adjustable switch contacts which operate in unison with the indicating dial readout to operate alarms, shutdown or automation processes. The OPL series is a flange mounting, indicating pressure gauge and switch. Adjustable high and low limit ungrounded contacts are used to operate alarm, shutdown or start- stop circuits. Pointer closure against either of the adjustable contacts completes the pilot-duty circuit. A SPDT toggle switch is provided to override the low limit contact for equipment start-up. Suitable for engines or electric motors with appropriate Murphy Magnetic Switch or Transformer Relay assembly.