The Bendix AD-9 air dryer is easily serviced by disassembling it from the frame and removing the bottom cover bolts. The unloader located on the bottom housing can be removed and a kit installed. The kit comes with new o-rings, spring, valve and seat. The main filter which is filled with dessicant absorbs the oil and moisture that accumulates in the air brake system.
Since the air compressor creates heat this causes moisture to build up, so this is why air brake systems have an air governor that unloads the compressor at 120 p.s.i. and signals the dryer to dump the build-up of water & oil in the bottom housing to atmosphere. That's the quick air release you hear when building up the air system, the air guage should be reading a minimum of 120 p.s.i.
The dessicant filter has a threaded stud attached so it can be easily removed during a service. The Bendix AD-9 is a very reliable component and is usually trouble free but if you notice a lot of oil coming from the bottom housing exhaust port then that's telling you the compressor is pumping out more oil than it should. Bendix has a splash card that you hold under the exhaust port, that gives an indication of how bad the oil loss from the compressor really is. The next step is to replace the compressor and of course, service the air dryer. Under normal conditions the air dryer can be serviced every 1-2 years depending on the condition of the air compressor and highway miles or hours of operation.
The Bendix Air Dryer also have a built-in heater wired up to sense cold weather and keep the unloader valve from freezing up. Every Truck & Bus air system has an air dryer installed from the factory, it's the most important preventive maintenance item and should not be neglected.
