Did you know that vehicles equipped with air brakes need to have the air tanks bled regularly? Otherwise accumulated moisture in the system could cause brake problems.

Most modern apparatus have an air dryer plumbed downstream of the compressor, and an automatic moisture ejector mounted on the primary or "wet" tank. Those devices are designed to remove most of the moisture in the air, but sometimes they can't catch it all. In areas where it rains often or the humidity is high, frequent brake applications can cause the moisture to flow past these devices and into the rest of the vehicle air system. Once inside, the moisture condenses with oil vapor from the compressor to form a gummy sludge that can clog brake valves. Much of it ends up in the secondary air tanks and needs to be bled off periodically. Installing quarter-turn or pull-cord drain valves in the bottom or lower ends of the tanks makes the job easier.

This feature offers a variety of short tips and facts about apparatus maintenance and testing. Look for it every month. Submissions of 150 words or less are welcome from our readers, subject to editing. Send them to Senior Editor Chris Cavette at cavettes@ix.netcom.com