Truck News

Feature

No Stopping Now

QUEBEC CITY, Que. - Officials with the Ontario Trucking Association (OTA), Canadian Transportation Equipment Association (CTEA) and air brake manufacturers were all echoing common concerns this fall, asking fleets and trailer manufacturers to look...


QUEBEC CITY, Que. – Officials with the Ontario Trucking Association (OTA), Canadian Transportation Equipment Association (CTEA) and air brake manufacturers were all echoing common concerns this fall, asking fleets and trailer manufacturers to look beyond legal requirements when spec’ing brakes for multi-axle trailers.

Sessions during annual meetings for both groups called for improvements including split air brake systems, low-air warnings to alert drivers of lost trailer brakes, and recommended components that could help prevent trailer brake failures in the first place.

“The bottom line here is (Canadian Motor Vehicle Safety Standard) 121 is a minimum standard,” said Ed Tschirhart, CTEA’s director of technical services.

The existing standards are largely a copy of Federal Motor Vehicle Safety Standard 121, which governs air brake designs in the U.S., but they were also designed with a focus on tandem-tandem combinations.

While less than three per cent of U.S. trailers have three or more axles, almost 30 per cent of Canadian trailers have the multiple axles, including the Michigan combinations that travel through Ontario, Quebec quads, and multi-axle designs that travel roads in British Columbia.

When all brakes are working, the vehicles stop within acceptable limits – additional axles come with additional brakes, after all. But Rolf Vanderzwaag, manager of maintenance and technical issues at the OTA, released a study last year that suggested spring brake priority systems built to the Standard 121 could unexpectedly leave drivers without trailer brakes, which is a particular problem with multi-axle vehicles.

A vehicle pulling a five-axle trailer will lose three times more stopping power than its tandem-axle counterpart if trailer brakes fail, according to Dick Radlinski, whose company was contracted to study the issue for the CTEA.

If all brakes are working, a tractor-trailer can stop from highway speeds within 276 feet, while fading brakes may need 395 feet.

But if a heavier six-axle trailer loses its brakes, its tractor will need 1,258 feet to stop in an ideal situation, and 1,798 feet to stop if brakes begin to fade.

Canada’s multi-axle trailers also have wider spreads that can add to the loads on individual axles, affecting application and release times when equipment is working as it’s designed, said Chitta Bera, OEM sales manager with Haldex.

Compounding matters is the fact that drivers can be unaware of the loss of trailer service brakes caused by problems as diverse as missing petcocks that allow air to drain from reservoirs, pinched airlines, or incorrect valve choices that affect control signals.

Granted, spring brake priority systems offer some advantages. Since they ensure spring brake chambers are filled with air before filling service brake air tanks, parking brakes can be released after an emergency application, and they protect against the dragging spring brakes that can lead to trailer fires.

(With 400 hp under the hood, a driver can pull away with dragging spring brakes without noticing any problem before the trailer catches on fire, said Bendix brake designer Chuck Eberling.)

They also ensure that spring brake systems can be quickly released when jockeying equipment in a yard.

The down side is that drivers can be unaware of problems with their trailer service brakes until they make a brake application.

Ironically, many of the recently recommended improvements were eliminated from the Standard 121 rules in 1990.

“A large part of the decision making was the fact that some people in the industry would say the system was too complicated the way that it was; the system was too costly,” said Kevin Roberts, OEM sales manager for Sealco. “Perhaps we’ve over-simplified.”

While plans for signals to warn drivers about trailer brake failures were once thought to be too complex, they can now be delivered by the same Power Line Carrier technology that has been developed to light ABS warnings in dashboards.

(Signals are carried over traditional seven-pin electrical pigtails.)

The splitting of trailer air brake systems can also make a dramatic difference in the event of a failure.

“If you split the system at least in two, even with up to five axles, your performance will be better,” Radlinski added.

By splitting a system from side to side on a tridem, for example, a tractor-trailer will still maintain 73.7 per cent of its stopping power if it loses half the trailer brakes. Quads would retain 70 per cent.

The idea isn’t that far-fetched. Logging trucks in B.C., for example, often have each axle protected by a dedicated air circuit.

But there are limits.

If the truck’s control line is damaged, all trailer brakes will be lost no matter how the system is split.

Related maintenance efforts could be improved by adopting the European practice of including fittings that can be used to inspect pressure levels in individual air lines and chambers, Roberts added.

“Make it accessible to people who work on this equipment.”

And pressure gauges could be mounted next to those that measure pressures in air suspension systems.

Trailer manufacturers should also invite the makers of components to scrutinize plans for air systems, he said, referring to problems such as the choice of an incorrect valve design that could be avoided.

And the training shouldn’t end there, he said.

“Drivers lack education on braking in loss-of-brake situations…Drivers do not know what to do with the red button.”

(For the record, the spring brakes should be applied in the event of lost service brakes.)

For that matter, mechanics need to be better trained, Vanderzwaag said, also suggesting the need to include pneumatic systems in periodic vehicle inspections.

“We need to make sure technicians know what they’re doing.”

Ultimately, the supply of air needs to be protected to help prevent failures in the first place.

The CTEA is recommending screens to keep contaminants out of gladhands, and wants gladhands mounted so they won’t draw in water when trailers are parked.

“If you’re pulling four axles or more, you need to consider using a constant duty air dryer unless you want freezing problems in the winter,” said Vanderzwaag, adding compressor sizes should also be carefully considered.

“A tractor designed for tandem-tandem operation cannot control a six-axle trailer,” he said.

A 16.5 cfm compressor, for example, will generate a mere seven cfm at 1,200 rpm – the size is based on the displacement of the compressor and not the air that’s flowing from the pipe.

“It’s highly unsafe,” he noted.

“But it’s not illegal.”


Print this page


Have your say:

Your email address will not be published. Required fields are marked *

*