Many of the RVs sold today have air brakes and for most buyers it is there first exposure to an air brake system. I feel that it is very important to know the basic components in the system and what they do.
An air brake system has the following basic parts:
The air compressor is used to maintain pressure for the braking system and the suspension. The air compressor governor should cut in when the pressure drops to about 100 psi. and should cut off at about 125 psi.
The foot brake, which is also called the service brake, is a valve that operates the brakes. Every time you apply the foot brake you are pressurizing the brake system. Pushing the pedal down harder applies more pressure. Letting up on the brake pedal reduces the air pressure and releases the brakes. Releasing the brakes lets some compressed air go out of the system, so the air pressure in the air tanks is reduced. Pressing and releasing the brake pedal unnecessarily can let the air out faster than the compressor can replace it. The normal operating range for air brakes is 90 to 120 psi, but a good rule of thumb is that you should never start moving with less than 100 psi. If the system pressure drops below 90 psi, you may not have full brake efficiency.
The parking brake is that diamond-shaped yellow knob that you push to release the brakes and pull to set the brakes when parking.
Ensure that when you leave the driver’s seat you have the parking brake set and the transmission in neutral. Coaches with an air brake system usually do not have a Park position on the transmission.
The warning buzzer and light should sound and light when the air pressure drops below half the compressor cut off pressure. Usually this occurs between 60 to 70 psi. If you hear the warning buzzer, or see the light while driving, pull over immediately in a safe area and stop. Apply the brakes once and come to a stop. Do not pump the brakes because each time you push on the pedal you use up your air supply faster. It is much better to make a controlled stop, in a safe location, rather than having the emergency brake engage when the pressure drops below the safe limit. If it does, that is where you stay. If that is the middle of the freeway that is where you are going to stay until you can rebuild pressure or a mechanic comes and overrides the system. When building air pressure the buzzer may not go off until 80 to 90 psi.
The emergency brake system is a spring-loaded brake that will come on automatically when the air pressure drops to a range of 20 to 45 psi. The emergency brake system is very confusing to most people. They think it is similar to the emergency brake in their car. It is a separate system from the parking brake and only engages the brakes when the air pressure drops below the limit.
The air storage tank holds a sufficient quantity of compressed air to operate safely. Some systems have multiple tanks, one for each axle, and sometimes a third for the suspension.
The pressure gage will indicate how much air you have in the storage tank(s). Some vehicles have two gages, and others have a single gage with two needles. You need to become familiar with the pressure gage(s) you have on your vehicle.
An air system will also have filters and dryers. They are there to keep the brake air clear and dry. Be sure to service/replace them regularly.
At this point I need to add this note. When I talk about coach air brake systems I am talking in general terms. I highly recommend that you do some research on your coach to see what you have.