A Positive Air Shut Off (PASS) valve is a safety device designed to monitor a diesel engine’s RPM. In the event of a diesel engine runaway, where the engine uncontrollably accelerates by using flammable gases from the ambient air as fuel, the PASS valve engages.

Positive air shutoff systems are used to protect people and equipment from diesel engine runaway. This occurs when a diesel engine ingests a hydrocarbon vapor and uses it as an uncontrolled fuel source. When this happens, the only way to effectively shut down the engine is by either removing the air or fuel supply.

Positive air shutoffs are designed to keep a diesel engine from over-revving and “running away”. This is a unique hazard with diesel engines because they do not require a spark for ignition and can continue to burn hydrocarbons in the air even when the diesel fuel is exhausted or the key is removed.

The positive air shut off system will stop the fuel supply without turning off the engine. Such technology allows you to take the necessary safety precautions without stopping your work. Installing the PAS in your truck allows you to comply with the safety requirements in several states.