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Dec 2, 2021


  • Technology

Corrosion is a hot topic discussed quite frequently in the heavy-duty trucking industry.  It’s a leading cause of the obstructed flow of power through the electrical system. But there is another system on a tractor-trailer that can also experience obstructed flow, and that’s the air brake system.  And there’s more than just corrosion at play.

Air Brake Systems

Heavy-duty commercial vehicles use air brake systems versus hydraulic brake systems because they are safer and more practical for larger vehicles.  Pneumatic brake systems use atmospheric air, which is everywhere.  Hydraulic systems require adding brake fluid, which would be challenging to manage and maintain on larger vehicles.  In a hydraulic brake system, when the brake pedal is depressed, pistons push the hydraulic fluid from a reservoir down the brake lines into the calipers, which compress the brake pads into the rotors on the wheels to stop the vehicle.  Air brake systems also use pressure, but with air behaving in a fluid manner.  When the operator steps on the tractor brake pedal to slow or stop the vehicle, air from the tractor’s air tank travels through the foot valve and through the service line to the trailer’s service valve. This air opens the valve allowing air stored in the trailer’s air tanks to enter the brake hoses into the spring brakes, turning the pneumatic force into a mechanical force, and apply the brakes.


Many components make up the air brake system on a tractor-trailer; mechanisms that engage and disengage the system, those that compress and hold the air, and the parts that create a pathway for air to flow.  With a focus on the latter, if airflow becomes obstructed and cannot move through the system efficiently, the system will fail.

Air lines and their coupled connections are susceptible to the pitfalls of corrosion and harsh operating environments.  Corrosion can create significant problems with gladhand couplings and loss of air pressure.  Frozen air lines in sub-zero temperatures can lose their ability to retract and recoil, creating sag.  Even improper selection and installation of air products can hinder airflow.  Phillips offers the following recommended practices and air products to create a clear and unobstructed path for airflow within the air brake system.  

Air Lines

Different types of air lines have their trade-offs when determining which is the best option.  Rubber air lines are heavier and more robust, whereas coiled cables are lighter but more susceptible to damage.  Coiled cables are prone to tangles and irreversible kinks, which restrict airflow.  Both are vulnerable to chaffing, nicks, and cuts.  Cables should be inspected regularly and replaced when damaged.  And when replacing air lines, the adapter fitting that connects to the tractor protection valve should always be replaced.  Using the old fitting from the previous air line can lead to a slow leak.

Additional practices to keep air lines unobstructed include proper cable selection installed with proper cable support.  Both ensure an appropriate working length.  When full working length is lost, there is the potential for damage and disconnect at the coupled connection on the trailer.  When cables are pulled taut, gladhands slowly become separated leading to a loss of airflow.  Depending on the application, coiled or straight, cable support springs should be installed to allow for maximum use of the working length. A single spring is needed to support coiled cables with the hose holder placed near the base of the first tractor-side coil rather than the middle of the coils. With straight applications, two springs should be used, one as the support spring, and the other as the working spring, with the straight air lines wrapped in one large helix that expands and contracts just as the coils would on a coiled air line.

When traveling in harsh weather conditions, select air lines for extreme cold, such as Phillips POLAR AIR®, to help prevent sag, leading to damage from drag on the deck plates. 

Air Connectors

Failure to maintain gladhands will prevent proper coupling, which will allow air to leak and leave the brake system open to moisture and debris.

Typical gladhands on the market are made up of an aluminum body that is highly susceptible to corrosion. During routine PMs look for corrosion build-up on the body and the gladhand’s inner cavity. Corrosion build-up that begins to chip away can enter the air lines, which can cause damage. Vehicles that operate in highly corrosive environments should consider switching to anodized gladhands. Wear to other parts of the gladhand, such as the dimple on the detent plate or deteriorating or loose connector plates, can lead to a weak connection, and gladhands should be replaced. Loss of tension during coupling and uncoupling is also a sign that gladhands need to be changed. If replacing the air lines and gladhands at the same time, opt for factory pre-installed gladhands. Gladhand seals can also be a culprit of air loss and one of the easiest things to swap out.  Always replace seals that look discolored, split, or damaged.

In addition to the traditional gladhands, Phillips also offers several specialty gladhands for different needs, such as swinger gladhands to avoid air line kinking, swinging with the truck as it pivots and turns for better movement of the cables.  And while keeping air lines obstruction-free is essential, a shorter path for air to exhaust can also improve uptime. The Philips QWIK-E® is a gladhand and quick-release valve combined into one, anodized for corrosion protection, and designed to release the brakes up to 50% faster than conventional methods to improve brake response time. With the QWIK-E®, air is released at the gladhand connection, instead of having to travel back to the front of the tractor, evacuating the system faster to get the vehicle rolling sooner. Last month Transport Topics discussed the more than 5,600 CMVs parked during Brake Safety Week. The Phillips QWIK-E® provides a solution to avoid some of the violations associated with brake drag, such as tire flat spots and reduced brake lining and drum wear.

Air Filtration Systems

Trailer air brake systems can become obstructed from dust, debris, and even insects that make their way into the air lines at the coupled gladhand connection. Gladhand screens and dust-flap seals are one solution but are easy to forget during service and also obstruct airflow when clogged.  An alternative to screens is an in-line air filtration system.  However, some do not offer service indicators, are difficult to maintain, and some even restrict air flow when clogged. 

The Phillips AIR-DEFENSE™ avoids the hassle that comes with other filtration systems available on the market today and maintains unrestricted airflow in the air brake system. Its Quick-Change Cartridge features a bypass mode that ensures consistent airflow, even when the filter is full. A non-resettable red indicator on the bottom of the cartridge pops out to notify the mechanic or operator when to replace the cartridge. And replacement of the cartridge takes minutes and can be done while on the road by simply unscrewing the old filter and replacing it with a new one, avoiding downtime.  

Air Tank Drain Valves

Condensation from compressed air in the air tank can sit in the tank and even travel through the system. Tractor air dryers play a role in dissipating quite a bit of this condensation but do not capture it all.  

Water and debris must be purged regularly to avoid scaling and corrosion in the air tanks and keep the entire system in good working order. The manual method of kneeling for 10-15 minutes every night to drain what remains in the system via a petcock or pull cord type drain valve on the air tanks can be cumbersome. Heated electronic drain valves automatically drain the air tanks, eliminating the need for frequent service. The Tank Saver from Phillips eliminates the need for service entirely once installed and can even integrate into telematics.

Multiple variables play a role in the path of least resistance of airflow in the air brake system. Proper selection and installation for the application and operating condition, as well as proper maintenance, will keep lines clear and unobstructed leading to uptime.