Parts + Service

TRP® Oil Coalescing Cartridges

A critical Part of the Truck’s Air System

The oil coalescing cartridge is a critical part of the truck’s air system. It is installed between the air compressor and the “wet tank” on commercial trucks and buses. The oil coalescing cartridge’s purpose is to filter out water vapor, aerosolized oil and other contaminants before they can reach the air tanks, valves and other downstream components. Essential to vehicle performance, these cartridges protect key components (including brake valves, emission controls and automated manual transmissions) by removing moisture and oil aerosol contaminants before they enter the system. The majority of today’s commercial vehicles rely on oil coalescing cartridges to perform this job. Oil coalescing cartridges use a substance called a desiccant to promote dryness and filters to trap oil and contaminants.

TRP® has partnered with an industry-leading manufacturer of oil coalescing cartridges for the aftermarket and for Original Equipment Manufacturers (OEM) to offer the TRP® Oil Coalescing Cartridges. Designed to deliver high-quality performance without a premium price point, these TRP® cartridges are ideal for aftermarket applications for vehicles progressing in ownership and age. TRP® Oil Coalescing Cartridges meet or exceed all OEM requirements and use 100 percent new desiccant. This helps the TRP® Oil Coalescing Cartridge remove water and oil aerosol from the air supply, ensuring the highest level of protection for the vehicle.

The Importance of the Right Dryer

In most parts of the world, there is always water vapor or humidity in the atmosphere. That means most of the air entering the compressor contains moisture. As the compressor does its job, it does two things:

As the air travels through the air lines that connect the compressor, reservoir tanks and various components, it cools. Cooling results in condensation. Condensation creates pools of water in the bottom of the truck’s air tanks. You will also find oil from the compressor along with other contaminants that made it through the compressor’s air filter in the water. This moisture leads to corrosion and bacteria, which causes components to work less effectively, increases maintenance costs and shortens component life cycles.

Along with the moisture, oil that blows past the compressor is also detrimental to the air system.

Oil can contribute to premature damage in a variety of components such as push-pull dash valves, spring brake modulating valves and brake chamber diaphragms. Oil-deteriorated seals can cause air system leaks that may cost points during a roadside inspection.

Choosing the right air dryer cartridge and replacing it at the specified maintenance interval will help maintain system performance, lower overall maintenance costs and reduce vehicle downtime.


TRP® Oil Coalescing Cartridges:

• Reduce the amount of aerosol oil and particulate in the air supply.

• Reduce aerosol oil thereby maintaining factory performance levels of downstream valves and components by not allowing oil to clog or slow valves.

• Extend the life of downstream valves by reducing the oil that can damage rubber seals.

• Reduce vehicle downtime.

• Reduce maintenance and repair costs.

• Maintain system performance

Desiccant-Type Filters

The desiccant-type air dryer uses specially engineered materials commonly known as beads to collect and absorb moisture. Desiccant air dryers have two operational cycles: the charge cycle and the purge cycle. During the charge cycle, compressed air, along with oil, aerosolized oil, water and water vapor, flows through the compressor discharge line to the supply port of the air dryer.

As air travels through the end cover assembly, its direction of flow changes several times, reducing the temperature, causing contaminants to condense and drop to the bottom of the air dryer. Next, the air flows into the desiccant cartridge. Once in the desiccant cartridge, the air flows through the desiccant bead and an oil separator. The desiccant removes water from the air and the separator removes the oil.

Air flowing through the desiccant becomes progressively drier as water vapor adheres to the desiccant material in a process known as “adsorption.” For more information, see Adsorption sidebar below. Dry, clean air exits the air dryer delivery port through the check valve.


Coalescing dryers use desiccant to hold the vapor. This process is known as adsorption. Adsorption is different than absorption. Absorption is the process in which a fluid is dissolved by another liquid or a solid. Adsorption is the process in which atoms, ions, or molecules from a substance (in the case of an air dryer, it is the water and water vapor) adhere to the surface of the adsorbent. In coalescing filters, that adsorbent is the desiccant. Since the water is held on the surface of the desiccant and not absorbed within, it can be carried off the desiccant and out of the cartridge during the air purge cycle.



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