The treadle valve saga continues
Faulty valves may be the cause of unexplained accidents
By Allan Powell
A serious problem with air brakes seems to have been over looked for several years, and could certainly point to causes of numerous accidents involving heavy-duty vehicles in which the cause was never determined definitively.
In cases where the driver lost the brakes and could not slow the vehicle on a downhill grade, he caught the blame for not inspecting the brakes for the correct adjustment. But more likely there is another more realistic cause for these accidents to occur, which may just answer any questions as to why so many accidents go unexplained in cases in which the brakes were not performing correctly at the time of the accident. It could also explain why there are no brake marks at the scene of the accident.
It requires a closer look at the problem of the air foot-control valve, also called the treadle valve — the brain of the air brakes. It is the first valve that supplies the correct amount of air pressure to the rest of the valves and brake chambers on the secondary side of the brake system.
Pressing down the treadle valve pressurizes the air brake canisters, pushing a rod to the brake adjusters with the correct degree of pressure as the brake pads press on the drum. The brakes will not work if the treadle valve sticks or does not perform correctly.
There are several ways the treadle valve can stick.
The driver will have no brakes if the treadle valve sticks in the up position and the plunger in the valve housing will not go down. Any accident will not be the fault of the driver.
If the plunger sticks in the center the air pressure supplied to the brake chambers will be just enough to cause brake drag, which in turn causes the brakes to heat up and catch on fire without the driver knowing. Also, the brake lights won’t come on. With the brakes hot enough to catch fire, the seals usually burn out and ignite the grease and tires, setting the rest of the vehicle on fire.
A treadle valve stuck in the down position can lead to brakes locking up and not releasing, causing the driver to go into a skid. Most of the times when the Treadle Valve freezes in the down position, the vehicle has been left sitting with no air pressure. The brakes will not release until the valve is replaced.
Recalls of the Treadle Value
The recalls of treadle valves over the years over the years should be enough to see that this problem has existed for a long time. The National Highway Traffic Safety Administration (NHTSA) has been recalling treadle valves since the 1970s with the latest recall coming in August 2012.
What’s causing so many problems with treadle valve? Why more issues now than ever before?
Yes, there are more vehicles with air brakes on the road today. But the real reason has to do with greater number of chemicals that come in contact with the treadle valve today, such as the liquid salt many states use on roads that often corrode the inside of the valve.
This loose corrosion can block the plunger and the valve and prevent the treadle valve from working properly — which can ultimately lead to an accident. It takes shaking or jarring to get the treadle valve working again.
Without disassembling the valve to inspect the treadle valve, the reconstructionist has no knowledge of this problem and leaves the actual cause of the accident unexplained.
A treadle valve with corrosion inside the housing can slow down brake reaction time enough to cause an accident. If the plunger in the valve is not smooth due to corrosion it can cause a brake reaction time failure or delay. Every second counts in the prevention of an accident.
At this point, we may never know how many accidents damaged treadle valves have caused in the past. But if mechanics, reconstructionists and drivers were more informed of this major problem, many accidents could be avoided in the future. BRM
A veteran truck driver of 30 years, Allan Powell is now a full-time consumer advocate for the prevention of accidents, and champions the cause of greater awareness of the hidden dangers of treadle valve corrosion, closer inspection and maintenance. Contact him at firstname.lastname@example.org.