The Murphy LM500-TF-PM Oil Level Maintainer includes a test feature that confirms both the float and switch are operating correctly with a single press of the test button. The LM500 series maintains the crankcase oil level of an engine, pump or compressor. Adjusted to the correct running-oil-level, it will replenish oil as it is used. The low-level switch will alarm and/or shutdown the equipment if supply oil is lost and the equipment continues to use oil. The LM500-TF-PM maintains oil level on any size engine. It also supports installations that require a 3-wire, snap-action switch. The form C (3-wire) contact allows a controller/annunciator to be wired as a closed-loop system, resulting in a reliable fault-sensitive circuit.

As crankcase oil level drops, the LM500-TF-PM float also drops and opens the Thumb-Valve. This allows oil to flow from the supply tank, through the LM500-TF-PM, and into the crankcase. When proper level is achieved in the crankcase, the LM500-TF-PM float rises, causing the Thumb-Valve to close off further oil flow. The simple and unique Thumb-Valve is non-clogging and provides a positive, leak-free seal.