Air Dryer: Air Reservoir Drain Procedure

by Arvin Meritor

To prevent serious eye injury, always wear safe eye protection when you perform vehicle maintenance or service. Park the vehicle on a level surface. Block the wheels to prevent the vehicle from moving. Support the vehicle with safety stands. Do not work under a vehicle supported only by jacks. Jacks can slip and fall over. Serious personal injury and damage to components can result. Remove all pressure from the air system before you disconnect any component, including the desiccant cartridge. Pressurized air can cause serious personal injury.

1. Begin with the supply reservoir. With the air system under normal operating pressure, momentarily open the drain valve and watch for evidence of moisture, i.e., a spray or droplets. If there is no evidence of moisture: Close the valve. If moisture is detected: Repeatedly open the drain valve for short periods of time, several seconds at most, until moisture is no longer visibly ejected from the reservoir. Wait several seconds between each opening to allow moisture to flow back to the drain valve area inside the reservoir. Once nothing is detected, close the drain valve and go on to the next reservoir.

2. If during the process of trying to eliminate all moisture from the reservoir, the air pressure drops to ZERO, leave the valve open for several seconds, then close it. The likelihood of draining additional moisture by leaving the valve open is negligible.

3. Repeat this process with all remaining reservoirs. This procedure is intended to remove all liquid from the reservoir without completely draining the air. The less the air compressor and air dryer have to work to refill the system, the more efficiently the air dryer will function. Completely refilling the whole air system volume every day puts an unnecessary moisture load on the air dryer, which will require additional purge and regeneration cycles in order to reach a stabilized dryness condition. If there is excessive moisture in the air system on a daily basis, one or all of the following procedures may be necessary. Check the system for air leaks. Replace the vehicle’s air dryer desiccant cartridge. Evaluate the vehicle application to determine that the correct components have been used.