Maintenance,Air Dryers/Compressors/Valves

The job of an air dryer replacement cartridge is clear-cut. But choosing the right replacement cartridge? Not so much.

You face an array of choices for this common component, which removes moisture from the air system before it enters your service tanks and harms brake valves. Making the wrong selection can mean downtime and increased service costs. But spec’ing the right cartridge doesn’t have to be hard – if you keep the basics in mind.

“It Eats Rocks”

First, a step back: Twenty years ago, most trucks had a dryer like the Bendix AD-9®, a tireless workhorse with robust packaging and a dryer cartridge that holds almost 4 pounds of high-quality desiccant.

It’s no surprise that fans of the tough AD-9 affectionately say it “eats rocks,” a measure of its durability in harsh applications. And it’s also no surprise that Bendix has built over 5 million of them, with almost 2 million still on the road. Because older compressors pass a lot of oil, all that extra desiccant in the cartridge is handy to soak up passed oil while still effectively removing moisture.

Oil passed by the compressor is the enemy of the air dryer. Mixed with water, oil plugs up valves. But it also coats the desiccant inside the dryer cartridge until, eventually, the cartridge can no longer remove moisture – which leads to excessive moisture in the service tanks.

In the last two decades, air dryers with spin-on cartridges began showing up. Their convenience proved to be popular and, today, more than half of the trucks on the road have an air dryer with a spin-on cartridge.

Spin-on dryer cartridges can be very efficient – when brand new, they remove about the same amount of moisture as the older AD-9. But they include a drawback: Spin-on cartridges contain only about half the desiccant of an AD-9, so their capacity to trap oil is also lower.

It’s also important to remember that spin-on cartridges use a standard mounting interface in North America. This standardization brings benefits, but it has also created a significant aftermarket for a variety of value brands. Many of these brands compete mainly on price and don’t always pay close attention to what’s actually inside the cartridge.

With so many choices, it’s easy to be confused. To help you know what you should be looking for, we offer our three simple rules.

Rule 1: For New Trucks, Choose a Standard OE-Grade Spin-On Cartridge

If your truck is still new and covered with a warranty, a “standard” OE-grade spin-on cartridge is your only replacement choice. We consider it “standard” because it’s designed only to remove moisture and some small particles, but not oil aerosols. It’s “OE grade” because it’s the exact same cartridge you get with a brand-new air dryer.

The desiccant inside the OE-grade cartridge is of the highest quality and provides the best efficiency. Depending on how you drive the truck and how much air you consume, you might replace a cartridge like this every two or three years. More frequent replacement might be required if the compressor passes a lot of oil or the truck is used for vocational service.

Rule 2: For Trucks with Oil-Coalescing Cartridges, Choose Something Similar

If your truck is under warranty, and was supplied with an oil-coalescing cartridge, replace it with the same product. Do not expose yourself to expensive repairs by substituting with a standard cartridge.

Oil-coalescing cartridges are being used more and more on new trucks and vehicles in the aftermarket. Bendix oil coalescing cartridges are the same size as standard cartridges and have the same mounting thread. The difference is that they contain a patented filtration system to remove oil aerosols.

Why is oil-coalescing important? Many newer trucks – those with newer emission controls and automated manual transmissions – contain a number of solenoid-controlled functions. These solenoid valves are typically more sensitive to contamination than traditional brake valves.

A cartridge with an oil-coalescing filter – the Bendix® PuraGuard® is one example – is designed to remove oil aerosols from the air system. Consider that an oil compressor can pass up to one liter of oil in one year. While the main function of the filter is to keep oil aerosols out of the air system, the side benefit is that it can also protect the desiccant – providing longer life and better efficiency across the life of the cartridge. Keep in mind that you can always upgrade any air dryer – including those with a standard cartridge – to an oil-coalescing cartridge like Bendix PuraGuard.

Rule 3: For Used Trucks, It’s OK to Choose Lower Cost, but Only with Proven Performance

If you’re looking to save money for an older truck, buy from an original dryer manufacturer to ensure performance you can trust while still at a price that’s good for your bottom line.

When your truck is getting older, is out of warranty, or if you’re getting ready to sell, you may be tempted to choose one of the many value cartridges available from a variety of brands. Be careful, however. These aftermarket cartridges may be imported by resellers who are not technical experts in this product category. The quality and long-term drying effectiveness of the cartridges will vary.

The most important element of an air dryer cartridge is the desiccant. And not all desiccant is created equal. Even those desiccants considered good aren’t always suitable for an air-brake application where the dryer cartridge is exposed to high temperatures, water saturation vibration, wild temperature changes, and pressure cycling. Failing desiccant can begin to clump, and at this point, it not only stops removing moisture but eventually turns into powder that can get into the air system and contaminate your brake valves.

Consider the Bendix® GC Spin-On Air Dryer Cartridge to meet your needs. Intended for out-of-warranty trucks that use a standard (non-coalescing style) cartridge, the GC – the letters stand for “Green Cartridge” – is new but the desiccant inside is a fully-tested mix of Bendix remanufactured desiccant and brand-new desiccant. That resultant mix provides efficiencies close to our new “OE grade,” and this desiccant mix is especially resistant to powdering.

As with most truck systems, the right components can make a big difference, even in something as simple as changing an air dryer cartridge. If you’ve got questions about the right choice for your vehicle or fleet, take a few moments for some research, or get in touch with us here at Bendix: Nobody knows air systems the way we do.

Learn more about Bendix air treatment solutions at, or contact us at 1-800-AIR-BRAKE.

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