No PAS, No Entry: Mechanical Air Shutoff Installation


Installing a Positive Air Shutdown system gets your work truck one step closer to contract work in mining, petroleum and forestry markets

(By Bruce W. Smith/Senior Editor)

PAS. It’s a small device that can be held in the palm of your hand, yet it’s the most important safety item on diesel pickups working within a number of industries.

If your truck isn’t equipped with one, forget about any chance at contract work in many lucrative markets.

The  PAS, which is officially known as a “positive air shutdown system,” prevents a runaway diesel engine by providing a mechanical component that closes off the air supply, ensuring that outside fuel source through the air intake stops.

BD’s PAS kit is well-designed and robust.BD’s PAS kit is well-designed and robust.

A diesel engine only needs air and fuel to run. Cut off one and the engine quits.

But when that fuel source comes from outside the truck in the form of a combustible vapor, you can’t turn off the engine and  it will keep running and revving until it blows up using that volatile outside fuel source.

(Think spraying a can of starting fluid into the air intake but with an unrestricted supply.)

Installing a PAS makes diesel pickups compliant with regulations mandated by many contracts including septic tank removal, forestry project s and oil/gas well service.

PAS is operated in either manual or automatic mode via toggle switch.

One of the best designs is offered by BD Diesel Performance.

The easy-to-install kit ($1,135/US) comes with the controller, special boots and the automatic/manual shutdown unit.

All the parts are aluminum and stainless, so corrosion will never be a factor, and the electrical connections are waterproof.

It uses an in-line butterfly valve activated by a heavy-duty solenoid placed in the charge-air-cooler air intake line (CAC). The rpm sensor is wired into the main engine harness to pick up the crankshaft position.

The system’s computer, housed in a small control box, will trip the solenoid and close the valve automatically when the engine hits a predetermined rpm (4,600rpm for late-model Duramax) – or manually when the driver flips the dash-mounted switch to the “off” position.

Shutdown is almost instantaneous. To restart the engine requires opening the hood and physically resetting the trip mechanism on the PAS.

We installed a BD PAS kit on a 2008 GMC Sierra 3500HD  so it’d be all set to use for whatever work comes its way.