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.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.
