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Posted: August 1, 2014 by Rolf Lockwood

The model 2550 in-line filter from Sealco Air Controls

From the September 2002 issue.

Adding anti-lock brakes to trailers has brought many benefits over the years — safer stopping in general, increased stability in hard braking or on slippery surfaces, and thus better safety performance overall. In the absence of flat-spotting during panic stops, we’ve seen improved tire wear as well. ABS brought braking in North America into the 21st century, some might say, following our European colleagues and gaining from their earlier experience. And the upgrade was really pretty easy.

But there’s a nagging challenge that’s become more and more obvious as we gain experience with these systems: protecting against the accumulation of dirt and grit in the trailer ABS valves, which can eventually kill them. That’ll cost you money, maybe $1000 or so, depending on your system and your warranty situation.

So far we’re still in the honeymoon stage with ABS, and most valve failures have in fact been covered by warranty. Manufacturers tend to be a bit forgiving on this front when they’re introducing a new product and helping customers get through the learning period. But that may generate a false sense of security. What happens when the safety net runs out?

Tractor air is usually pretty clean so the tractor valves breathe easy. But it’s not always so for the trailer. Clean trailer air has always been important to braking performance and reliability; what’s changed is the cost.

The weak link in the system is the gladhand. When the wind whips up in dusty parking lots and blasts a bobtail tractor with sand and dust, the gladhand connections are open and are forced to eat a few grains of hard and abrasive crud. Of course dirt can also get on or into the connector as it’s carried or dragged over from the tractor. Dirt and sand particles can then fly along the air lines until they reach their final resting spot inside expensive trailer ABS valves.

There’s actually a wide variety of stuff to cause the system harm, from dead bugs to oxide from the gladhands.
There’s a screen inside some valves, but you’ll void your warranty if you open it up to clean it, so you leave it there. As time goes by, more and more dirt gets in, and your valve starts to leak or stick. If the warranty is over, you’ll be laying out that thousand-dollar bill by the time the valve is replaced. Then the dirt cycle starts again and another valve will be needed some time down the road, depending on how clean you can keep the air supply to the trailer.

Regular draining of your air tanks may get some of the dirt and sand out but if enough is getting into your system on a regular basis, it’s just a matter of time until failure.

Swivelling gladhands on trailers — well, those that actually work and swing back to seal off the opening — are good in theory. But if you look at a row of trailers, you can see that many are damaged or they’re stiff and don’t fully close. Trouble city.

And have a look at how your drivers store the gladhands on the tractor. If they’re careless, you’ve got a source of dirt. If not, they’re saving you money and you should encourage them to keep doing it.

“We’ve had minimal problems with valve failure due to contamination,” says Geoff Eaves, fleet superintendent at TST Overland Express in Mississauga, Ont. “A big part of this is due to our drivers properly storing the tractor gladhands when not in use.”

Vic Wintjes agrees with that principle wholeheartedly, but has seen lots of evidence of carelessness over the years.

“If you’re not careful with storing the gladhands on the tractor when parked or bobtailing, you’re sure to have valve problems,” says the former maintenance chief for the huge Canadian Tire trailer fleet, now an independent consultant with his own firm, VW Transcon Services, also in Mississauga. “Walk by a row of parked tractors and see how many have the airlines properly hooked on the dummy gladhands.

“The biggest problem is gladhands lying on the deck of the tractor with the openings facing up,” says Wintjes. “A gladhand is like a catcher’s glove — it’s good at trapping anything that comes close to it.”

The genesis of this story comes from Ray Camball, fleet sales manager at Trailmobile in Mississauga, Ont. He noticed that ABS valve failures were becoming a concern for major fleets running various brands of trailers, and he decided to look into it. Among other things, he found a simple
$30 solution from Sealco which we’ll get to in a paragraph or three.

There are others as well, like the $300-or-so Bendix System-Guard, an air dryer designed specifically for trailer brake systems.

A simple first approach to catch some of the dirt is the filter screen that’s available with Phillips gladhands. According to Camball, Trailmobile has gone standard with this screen. It’s not the magic cure-all, but at least it will keep the larger particles out, he says.

Drivers need to be aware the filter screen is there in case it does become plugged or restricted. It’s fairly easy to pry out the rubber gladhand seal and blow out the screen without needing any special tools. But a screen is still no substitute for care when handling the air line between tractor and trailer to make sure it’s kept clean. Some fleet people worry about moisture freezing on the screen if the air is not dry or if snow blows into the gladhand.

There’s a balance between the size of the hole openings and the air-flow restriction of the screen so a screen with ultra-fine filtration would be impractical. For example, a “100” mesh stainless screen has openings of about 5.5 one-thousandths of an inch. Sure, it’s a pain to have to clean out a screen, but it’s cheap protection.

The model 2550 in-line filter from Sealco Air Controls has been around for some 20 years, used reliably by some big U.S. fleets like Yellow
Freight and Walmart. Closer to home, Allan Thompson of Buckham Transport in Peterborough, Ont., has used it for four years now and has seen trailer-valve failures fall right off. He says he finds a surprising amount of “crud” in the filters when he looks at them during normal maintenance checks.

Note that it’s recommended for installation on the red supply line, not on the control line — at least not without OEM approval, because it could affect air flow and brake release times.

With its simple construction, easily cleaned 80-mesh screen filter (just blow it out), and low cost (about $30 on new trailers, not much more as an easy retrofit), it would seem to be a natural piece of insurance. In fact, Camball is urging trailer buyers to spec it routinely.

“Even with drivers who are careful storing gladhands, an in-line filter is a good safety net to protect the expensive ABS air system,” he says. “It only takes one mishap to foul your system so I wouldn’t want to see anyone order a trailer without a filter.”In Europe, where ABS experience is extensive, you’ll find a broadly similar (although smaller) in-line filter in WABCO trailer ABS systems. Model number 432-500, its replaceable filter can trap particles from 80 to 140 microns (3 to 5 one-thousandths of an inch). Unlike Sealco’s 2550, it has
a bypass function.

If the filter becomes blocked, the filter cartridge is pushed upwards and air will flow through without being filtered in order to keep the ABS functioning. The WABCO European web site suggests that it should be cleaned every three to four months.

That filter is not part of the North American MeritorWABCO trailer ABS offering, but Tom Parrott, engineering manager, vehicle control systems, says a similar one is in the works. He says the European filter cannot be used here because the fittings are metric, but they do have it in stock on
this side of the pond (for use in exported products) and will sell it to you if you want to bear the cost of conversion fittings. Note that its small size —
possible because European trailers aren’t uncoupled very often and thus don’t ingest much dirt — may make it unsuitable on this side of the Atlantic anyway.

While Parrott wouldn’t comment specifically on the Sealco product or any other filtration option, he did say that a blow-by feature is important.

“We would recommend the use of a filter that maintains air flow,” he told us. You can also infer that if you use a filter without a blow-by function, you’d better clean it regularly. Brake timing is the issue, of course, and any filter blockage could alter that timing significantly. Parrott adds that if you’re going to use an in-line filter on multiple-trailer trains, you may also need to spec a booster valve to maintain that air flow.

“First, we’d like to see the gladhands being covered,” he says, noting that a common maintenance practice — pressure washing — plays havoc with cleanliness in the trailer air system. Fat chance, you may say, but he suggests you ask your wash crew to bag the gladhands before the water-and-detergent attack begins.

Over at Haldex, ABS product manager Duane Stocksdale says this contamination issue has been on their front burner for a while.

“It’s a problem,” he says, adding that training at the shop and fleet levels hasn’t helped enough. As a result, the Haldex FFABS (Full Function ABS) valve now has filters built in to both air ports. The control-port filter was added in late 1999, the supply-port one within the last few months.
They can be serviced in the field inexpensively (about $5 a filter).

“We chose to be pro-active,” Stocksdale says. “It’s an evolving improvement. We would still support good maintenance practices on the gladhands, and putting filters in those gladhands as well.”

The Bendix approach includes the year-old System-Guard air dryer made specifically for trailer brake systems to protect against both moisture and solid contaminants. About a foot long and four inches square, System-Guard acts as a buffer, the company says, absorbing moisture in wet times and releasing it in dry times. It doesn’t have a replaceable cartridge; instead, the entire dryer is replaced at established service intervals. It mounts directly to the trailer frame, with a 30-minute installation time and an expected lifespan of five to 10 years. It needs no maintenance at all.

The bonus, of course, is that it also helps ensure that the air suspension works properly. Note that it incorporates fail-safe bypass valves in the “unlikely” event that the dryer is obstructed.

On the moisture front alone, Bendix has made the R-12 DuraDrain relay valve standard on trailer ABS systems with the MC-12 controller module.

This MC-12 combines the R-12 DuraDrain with the control and diagnostic features of the EC-12 electronic control module. It drains liquid ordinarily trapped in the control line and expels it out the relay valve’s exhaust port and doesn’t affect normal valve operation. Air pressure pushes moisture inside the control line into the relay valve.

When the brakes are inactive, the check valve is open, expelling moisture through the drain port built into the relay-valve piston. When the driver presses the brake pedal, higher control-line pressures close the check valve, maintaining normal valve operation.

Larry Gillis of Bendix says the bottom of the MC-12 ABS modulator is basically the same as the long established R-12 relay valve but with extra enhancements. He also warns that poor diagnosis of apparent valve problems often leads to parts being replaced that don’t need to be. For example, a spring-brake leak can cause “hissing” at the valve, which often gets replaced in error. Not a new story, but worth the reminder.

Clean air is critically important to any brake system if its performance is to be maintained and downtime minimized. With expensive ABS equipment on board, the motivation to keep it clean should be that much more intense. There’s a safety angle, too, of course.

There are dreadfully simple solutions like 50-cent Protect-o-Seal gladhand flaps, but they can come off or break (and then can enter the air system in small pieces). That implies the need for the Phillips 30-mesh (600-micron) gladhand screen.

If you’re still worried, the $30 Sealco 2550 is mighty cheap and apparently does a good job. Just remember to check and clean it regularly. And then there are more expensive answers like the $300 System-Guard from Bendix.

Any ABS valve is a sophisticated piece of equipment, and while some maintenance folks have been able to take an out-of-warranty valve apart to clean it and get it working again, this is definitely not recommended. There are precision parts in there that may not perform as well as when originally manufactured. ABS valves, if they’re allowed to breathe clean air, shouldn’t need this treatment anyway.

And the starting point is simple enough: by one means or another, keep those gladhand openings closed. If you can’t depend on drivers to help you out there, then filtration of some sort would seem to be in order.


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