How To Install A Positive Air Shutdown System
PAS kit a must-have upgrade for many mining, forestry, refueling and petroleum contract work
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 in or around petroleum production facilities. If your truck isn’t equipped with one, you’re not getting onsite.
The device is called a positive air shutdown system, or PAS.
If you are a contractor who has spent much time around the mining and petroleum-production trades, PAS devices are old hat.
But bring up the subject to the typical construction or landscaping contractor who is trying to expand their business and you’re more than likely to get a blank stare.
The operation of a PAS is very simple: 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.)
To prevent a runaway diesel engine there has to be a mechanical component that closes off the air supply, ensuring that outside fuel source through the air intake stops. Hence, the PAS.
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.
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.