Air System Care: Discussing Desiccants

Regardless of the season, water in your truck’s air brake system is never good – but water in the winter creates unique challenges, as cold temperatures create the possibility for freeze-ups and unexpected downtime.

Preventing water from collecting in the service air tanks starts with maintaining your vehicle’s air dryer. That sounds pretty simple, but fleets and owner-operators need to be aware of best practices and how to avoid potential issues.

Differences in Desiccants

Within an air dryer, it all starts with the desiccant – the small beads inside the dryer cartridge that attract moisture during a charging cycle and release that moisture during the purge cycle.

I often hear comments like “all desiccants are the same” and “new desiccants must be better than remanufactured,” but as I work closely with our engineers here at Bendix, I’ve also learned a lot about what makes a good desiccant and how that affects dryer performance.

We’ll start with that first comment: If you spill out desiccant on a table and compare Bendix versus anyone else, it does appear really similar in most cases. It’s not something you can hold in your hand and say, “Now that’s a really good-looking desiccant!” As a result, it’s something that most people don’t give any extra thought, relying on the supplier to manage.

Desiccants are typically derived from silicon dioxide or aluminum oxide, and they are used everywhere: Open a bottle of aspirin, and you’ll find a small desiccant bag in there. A truck’s air system is unique, though, in that the desiccant is compressed by a spring and subjected to tens of thousands of pressure cycles at a variety of temperatures and ambient humidity levels. More often than not, the desiccant in a truck’s air dryer is subjected to high temperatures, and is processing hot air that is saturated with moisture while also squeezed under pressure by the truck’s air compressor. That sort of continuous cycling is hard on desiccant life.

As part of its comprehensive ongoing testing program, Bendix evaluates the capabilities of desiccants using several methods. First is a standard SAE dryer efficiency test that tells you how much moisture the desiccant can remove at a defined “dew-point depression.” Second is a wet-attrition test that evaluates the desiccant’s resistance to wear under the conditions that are typical on a truck’s brake system. The wet-attrition test tells you how well the desiccant will hold up when saturated with water and under vibration – like on a truck. The third is a crush-strength test that measures the desiccant’s ability to resist breaking down in the harsh reality of a truck’s air dryer.

When fleets replace their air dryers or air dryer cartridges, they have a choice of “service-new” (an exact like-for-like replacement); remanufactured; or clone products, which are look-alike, often imported products that have the same form, fit, and function as the original manufacturer’s product, but are not built under the same exacting standards.

You can almost never go wrong with buying a service-new product from the original supplier. Yes, you’ll pay more, but those products are built with the same quality requirements as mandated by the truck builders, and those standards are essentially zero-defect. OE dryer manufacturers closely monitor their desiccant suppliers and continually monitor incoming product, which can sometimes vary from batch to batch.

The Benefits of Remanufacturing Desiccants

Bendix’s remanufactured desiccant is a proprietary mix of new and reconditioned material. Bendix remanufactures its own desiccant, which reduces the amount of material sent to landfill, while providing a low-cost but also high-quality source of desiccant used in remanufactured air dryer cartridges. We’ve got four decades of reman experience under our belt, and a pioneering history with dryers that goes back even further, so there’s no one better equipped when it comes to technical know-how in this area.

A high-quality desiccant is specifically selected for air dryers and can be reprocessed to provide like-new performance. Bendix’s remanufactured desiccant mix achieves efficiencies that are similar to brand new.

Let’s address the common belief that new desiccant has to be better than remanufactured. When Bendix evaluates clones of our service-new dryer cartridges, we sometimes find that when brand new and out of the box, the clone’s desiccant will perform satisfactorily to the efficiency test. Give it a few months, though, and that performance degrades significantly. We see in our wet-attrition testing, for instance, that many new clone cartridges with new desiccant begins to fail in just a few weeks of normal operation.

On the other hand, when Bendix remanufactures its desiccant, we start out with a high-quality product, which is directly suited for trucking applications. The remanufacturing process produces desiccant with efficiency that is close to brand new, but the long-term durability is nearly equal to new. That means in the long haul, Bendix remanufactured desiccant nearly always outperforms the new desiccant that we see used in clone products.

The bottom line is that you can’t go wrong with a service-new product air dryer or a genuine remanufactured Bendix dryer no matter what time of year you’re operating – from winter’s cold to summer’s heat and humidity.