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Listen Up for Air Supply Problems

By on July 1, 2018

Frequent Air Dryer Purging Could be Sign of Pending Trouble

It only takes about one week for anyone who’s driven an OTR truck to realize the importance of having your brake system operate at peak efficiency. Being in close proximity to other trucks running at different Interstate speeds can be nerve-racking enough. Mix in the crazy antics and total lack of respect for trucks and drivers exhibited by some four-wheelers, and you quickly realize great brakes go a long way toward preventing bad breaks on the Big Road.

Monitoring your entire braking system and having it checked regularly should be at the top of your maintenance checklist. In this installment of Maintenance Matters, I would like to address a braking subsystem that can be easily overlooked. Specifically, have you ever heard your air dryer purging frequently, but your air gauges hardly move?

This condition can often be traced back to an air leak in your truck’s air supply subsystem. It’s comprised of your air compressor, air governor, air dryer, wet tank, and all related lines. This braking subsystem is typically not monitored by air gauges, because the Code of Federal Regulations Standard 121 only requires a pressure gauge in each service brake system, but not the air supply subsystem. This means you can have a leak in the supply subsystem, and your gauges may not move at all. The only indication that you have a leak may be the frequent cycling of your air dryer purge valve. While you’ll be more likely to hear an air leak once your truck’s engine is shut off, sometimes these leaks are not so obvious.

How Your Governor Works

Knowing we’re not talking politics, let’s dig a little deeper into how your governor works. It monitors the air pressure in the wet tank. Once the air pressure builds to the set maximum of the air governor, it will open and send air to the air compressor to unload or stop the compressor from building any additional air. At the same time, it sends air to the air dryer to start a purge cycle of the air dryer, so it can clean itself with a blast of air. Once the air pressure reaches the set minimum requirement, the air governor will shut off the air to the compressor unloader, causing the air compressor to once again start building air.

The air brake supply subsystem has proven to be very challenging to many in the trucking industry, but I believe this subsystem is very simple and so are most of the root causes of any defects. For example, if your unloader valve in your air compressor is sticking, the air pressure may build slowly, not at all, or it may build too much air pressure. The cause may simply be that water in the wet tank has not been drained daily.

Dangers of Water Buildup

When water builds in your wet tank and the governor opens to tell the compressor to stop building air, some of that water will travel with the air to the unloader valve in the compressor. Over time, this important valve will begin to stick, and you’ll have air pressure buildup problems or very high air pressure in the system. You may end up needing an unloader rebuild kit, new compressor head, or in some cases, a new compressor. Avoiding these significant expenses comes back to regularly performing the inspections and simple maintenance items as required.

The air supply subsystem is isolated from the rest of your truck’s air brake system by two check valves. They allow air to travel from your supply subsystem but will not allow air to travel from your service brake systems back to the supply subsystem. The configuration of these  check valves helps protect your primary and secondary brake systems, in case you get a large air leak in your supply subsystem or either the primary or secondary system.

This 121 Brake Standard requirement helps provide air in either the front brakes or rear brakes of your tractor in case of a catastrophic air leak. Though your brake supply subsystem isn’t a frequent topic of discussion, it must be properly maintained, or you may find yourself prematurely needing major repairs of your air compressor, governor and/or air dryer.

If you suspect that you’re having a problem with your air supply subsystem, you can avoid any pending troubles by having the brake experts at any TA Truck Service location across the country check it out.

About Warren Eulgen

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