Maintaining Air Brake Systems

It's important to make sure that air brake systems are

dry before the cold weather comes. That was a message that Bob Pawluk, of Bendix, delivered at the American Public Works Association Michigan Chapter's Winter Vehicle Maintenance Tips seminar in Frankenmuth on November 2, 2005.

"Don't wait until they freeze up, because that will be too late. The idea is to perform maintenance before problems happen. It's a lot easier and cheaper to drain out the air systems. Make sure the air dryer is cycling properly," Pawluk said.

Pawluk said that it is important to know what comes out of the air brake system when it is drained and how much comes out. He said that if a handful of material comes out of the tank in a four- to six-week period of time, that is normal. "If you have more than that coming out, then there is a problem," Pawluk said. Air brake air tanks collect the most water in the summer when the humidity is the highest. It causes the most problems in the winter when the weather is dry. Fall is the best time to get the water out.

Pawluk said that alcohol-based products used to remove water from air systems are harmful and dangerous.

"When you have an air system freeze-up out on the road, how do you get the vehicle moving again? You use something to warm it up. What happens when the valve opens and some of this alcohol-based product starts coming out? This is dangerous," Pawluk said.

"Be aware that even if you don't think that there might be any alcohol in there, the operator may have already dumped some in. So, if you are going to put an open flame around the air system, be prepared." Alcohol also washes away the lubricant. Valves need to move in order to work the brakes. If the valves are not lubricated, the brakes may not work. Also, the brakes might not release if the valves are not lubricated and this would cause premature wear of the linings.

"So, anytime you're getting into issues with brakes, one of the things that I recommend is to go back to the air tank and drain the tank. Smell what comes out of it. If you smell alcohol, realize that part of the problem that you're experiencing may be caused by what's inside of the tank. From a liability standpoint, if you have some alcohol-based product in your facility, put it away for your use only. Don't leave it where the drivers can get at it. The alcohol-based product is for emergency use only. If you have to put some in, get the vehicle back into the garage and completely drain the air tank system, because the alcohol will damage valves," Pawluk said.

He said that an air release through the purge valve should last approximately 20 to 30 seconds. If the air release is longer or shorter than that, then something is wrong and the air brake system should be checked.

Pawluk recommended rebuilding the air dryer system once per year. The minimum that an air dryer system should be rebuilt is once every three years.

Pawluk said that the federal government wants trucks to stop at shorter distances than they currently do. The new requirements are expected to go into effect in 2010.

"Some of the truck manufacturers are working on this. We're seeing wide brakes and air disc brakes on vehicles right now. If you currently have some issues with certain trucks and certain operations that you must do with respect to braking, there are some things you can do right now. This is new equipment, it is not retrofitting," Pawluk said.

Dave Truckenmiller, sales manager for Muncie Power Products, Inc., discussed the proper use and care of hydraulic systems.

"Hydraulic systems are built for a specific amount of flow. You can't just make a decision to run it faster by putting a larger pump on it or a faster power take-off (PTO)," Truckenmiller said. He said that when something is done outside of what the hydraulic system is designed for, there is a risk of doing damage to the hydraulic system.

"If you create more flow than the system is built for, you're going to do a lot of different things to that hydraulic system. One of the first things that you're going to do is send your filters into bypass. Most of the filters in your hydraulic system have a bypass indicator on them. Those bypass indicators are hooked to a spring that is set up to bypass at a pressure differential. If the pressure is different by 15 or 25 pounds, depending on the differential strength, it will send that filter into bypass," Truckenmiller said.

"If you put more flow through your system than what that system is made for, you're risking going up over that pressure differential and sending that filter into bypass.

"The filter is there to keep the oil clean. The micron rating of the filter is telling you what size of contaminant that it will remove from your system. Systems that operate in the neighborhood of 3,000 pounds per square inch (PSI) need to have filters that have a micron rating of 10. That means that the filter is going to take a contaminant out of your system that is larger than 10 microns. A micron is approximately 1/1,000,000 of a meter.

"If you look in your system and you can see contaminants, then you have a lot of trash in your system. That's why your oil vendor is probably telling you that your storage capability needs to be in tanks in a fixed position where you run that oil through another filter before it goes into the vehicle. You're taking new oil, running it through a filter before it goes into the vehicle. You do this because a good 10-micron filter is going to clean the oil better because when the oil is processed, they can't do it in the small volume that it takes to clean it that well."

Operating speed is one way to check the bypass indicators. Bring the system up to the speed that it is going to be operated at and see if the filter is going into bypass.

Truckenmiller said that if there is a contamination failure, the hydraulic tank should be drained and the hydraulic system must be cleaned.

"If you think the oil is good, pump the oil through a filter buggy that has elements that will clean it and then pump the oil into a clean drum. I think that if you have a contamination failure, you're probably wasting your money by doing this though," Truckenmiller said.

Once the tank has been cleaned, the filters should be installed and clean, new oil should be put back into the system. The oil should be run several cycles for two or three days on the street, extending and retracting the cylinders. The filters should then be replaced with new filters. This process will thoroughly clean the system.