Air handling systems on big trucks.

If you have been near a big truck that is running you have probably heard the fairly loud “pssssst” burst of noise. That is the sound of the “Purge Valve” doing it’s job.

The air system on big trucks is an integral part of the whole. The air compressor under the hood and in the engine compartment has to maintain a constant pressure in the tanks to service many functioning parts on a truck.

The air bags at the rear of the trucks make the ride easier.


There are air bags under the cab of the truck that also make the ride easier.


You can’t really see them. There are two air bags and each are fairly small.


The brakes are run on air. There is an air chamber on the brake pods. One for each set of wheels. Two for the front axles and four for the rear axles.

These brake pods are from the trucks in Massachusetts. The rust is from the chemicals used to melt the snow and ice on their roads.


We have automatic transmissions in these International ProStar trucks we are delivering to Michigan.



The air system is used in the shifting of the gears. There is an actuator within the transmissions that rely on steady air pressure.

The seats of the trucks are raised and lowered with the aid of air. Once again, these photos are from the Massachusetts trucks.


This is our second set of trucks out of Van Buren, Arkansas going to Oak Park, Michigan – a suburb of Detroit. My first truck had a problem with the “Purge Valve”. It would stick open sometimes and I would lose air pressure.

Getting off I-55 in St. Louis, Missouri to get on I-70 there was a mile long back up of traffic due to a car stalled at a busy junction point. Using the brake as I had been I noticed my pressure gauges going down. That is NOT a good thing to see.


Right where this truck is on the exit ramp to I-70 is where I lost all my air.


I caused another mile long back up when I had to get out of my truck, crawl underneath it and fix my stuck open purge valve.

Here is a video I took of doing just that. Only this video was taken in a hotel parking lot and not on the highway. You will have to click the link to view the video.

I love my job…I love my job….I love my job. Maybe I can convince myself to hang in there for a few months longer.

Or not.



About Message In A Fold

I am an over the road truck driver in Drive-Away Transport part of the year, and the sole bookkeeper of this operation the other part of the year. I do a lot of whining until I can get in my craft room and play with paper and glue. View all posts by Message In A Fold

2 responses to “Air handling systems on big trucks.

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