Maintenance,Air Dryers/Compressors/Valves

You like saving money, right?Well did you know that a properly maintained air treatment system can help save thousands of dollars in costly service and vehicle downtime?Sure, it’s easy enough to regularly check a truck’s air system for leaks by conducting a 90 to 100 psi brake application and following it up with a walk-around inspection, keeping an ear open for the telltale hiss of escaping air. But there are also several simple, straightforward ways for owner-operators and small fleets to help reduce the risk of leaks in the first place by keeping close tabs on air system operation and maintaining air quality.

What to Watch For

Air tanks should be manually drained regularly: At least every three months for a typical line haul truck, and as frequently as once a month for trucks with high air demand, such as residential refuse trucks and other severe service vehicles.

While draining the air tanks, keep an eye on the drain valve and note whether it’s discharging excessive water or a mix of oil and water – either one is a sign of potential trouble. A lot of water coming out of the drain valve signals that the system’s air dryer isn’t removing enough of the moisture in the air, while a water/oil mix indicates that the dryer’s desiccant bed has been contaminated by oil aerosols passing in the compressor. Typically, a thimbleful of water is acceptable.

Keep in mind that ambient temperature shifts of greater than 30 degrees Fahrenheit can cause

a temporary accumulation of moisture, so if a significant temperature change took place in the previous 24 hours, just continue to operate the vehicle under normal conditions. The small amount of water that may have condensed due to the temperature shift will be reabsorbed by the dry air once the vehicle is in operation. To be safe, check the air system again after a week.

Other points to check include the compressor’s unloader – watch for excessive oil buildup – and the purge valve. Purge valves can be susceptible to corrosion and damage, particularly from winter road treatments, and can also attract an accumulation of dirt, oil, and water on the exhaust outlet.

Air Dryer Keys

Naturally, Bendix recommends sticking to the manufacturer’s air dryer cartridge replacement schedule – although, again: Dryer life cycles will vary depending on things like the application and operating environment. We also advise replacing the dryer’s purge valve at the same time, using a high-quality, original equipment component. Replacing the purge valve takes less than 5 minutes.

Because air system cleanliness relies so heavily on the dryer cartridge doing its job, this isn’t a place to cut corners. Given the risk that oil aerosols pose to air system components – corroding seals, valves, and diaphragms, for instance – oil-coalescing cartridges are the best choice. (I can’t help but point out here that the design of our Bendix® PuraGuard® filter actually removes oil from the air before the air passes through the dryer desiccant, which extends the cartridge’s life and effectiveness.) Replacing a standard cartridge with an oil-coalescing one is an easy upgrade to improve air quality: Just make sure that if a vehicle is already using an oil-coalescing cartridge, replace it with another one.

We have plenty more information on air system maintenance available for deeper dives in our free courses on dryers and compressors at the Bendix On-Line Brake School, and a detailed look at Bendix oil-coalescing technology in this Tech Talk from the 2017 Mid-America Trucking Show.

Protecting the air that helps keep truck systems like brakes and automated manual transmission systems running safely and smoothly should be a priority. But it doesn’t need to be a hassle.

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