At first glance this may appear to be a very simple and insignificant device. However, Electronic Positive Air Shutdown (EPAS) is likely the most important safety component you can install on your diesel truck.
As a contractor/supplier to the Canadian oil & gas industry, this unit is a must-have on all of JT Hotshotting’s fleet trucks. Not only does it save your diesel engine from a runaway situation but it’s also mandated in the CANADA OIL AND GAS ACT. Without it, you’re not getting on any work site.
“Section 13 (4)(b) a shut-off valve that is located between the engine air inlet filter and the induction system flame arrester and that is capable of being closed automatically by the engine overspeeding device and manually;”
How The Electronic Positive Air Shutdown (EPAS) Works
Diesel engines only need 2 elements to run – air and fuel. Cut off one of these and the engine will stall. However, when your fuel source comes from outside of the truck in the form of hydrocarbon vapour, simply turning off your ignition or killing the diesel supply will not shut down the engine. As long as that volatile external fuel supply has access to your intake manifold, your engine will continue running and over-revving until it grenades.
Most late model diesel engines already incorporate an electronic throttle body (butterfly valve) just before the intake manifold (charge-air-cooler side) to aid in EGR function by partially restricting air flow. The BD EPAS unit simply connects directly to this unit and will completely close the valve to shut off the outside air supply when it senses the engine revving higher than a predetermined level. On Cummins 6.7L engines the threshold is 4200 rpm. The EPAS module reads RPM’s through a secondary connection to the crankshaft position sensor.
Alternatively, there is also a dash mounted switch which the driver can flip to the “off” position.
In both cases, the in-line butterfly valve will remain closed until the engine RPM drop to zero and for an additional 5 seconds afterwards. The valve will automatically reset itself to the open position once the shutdown process is complete.
What If My Truck Doesn’t Have An Electronic Throttle Body?
There’s no problem at all. There are other BD PAS (Positive Air Shutdown) kits available and while they may be a bit more labour intensive to install they still yield the same result and actually cost around the same as the electronic EPAS kit. The difference in these kits is that they provide you with the missing butterfly valve.
The only drawback with these kits is that in order to restart your engine after an emergency shutdown, you need to open your hood and physically reset the trip mechanism on the PAS.
There Are So Many Various PAS (Positive Air Shutdown) Systems Available. Which One Should I Choose?
We recommend the PAS systems from BD Diesel Performance for a few reasons. Firstly, they are local to us and have products readily available. Everything they manufacture is incredibly easy to install and is frankly top shelf quality backed by a solid warranty.
BD offers both the Electronic Positive Air Shutdown (EPAS) kit and Positive Air Shutdown (PAS) kit.