Jon Wehrenberg
10-06-2011, 06:18 AM
At Hector's air system seminar at POG X Loc made the comment that if all his air gauges (primary, secondary and aux) are at zero his aux compressor will simultaneously charge all three systems. I stated he had something wrong with his coach because aux air should not be capable of charging the brake systems. Hector said I was wrong. Hector was half right, and I was half wrong. Hector was also half wrong, and I was half right.
While this may seem like minutia to fellow gear heads it is important for everyone to understand exactly how their coach air systems work because this could be a safety issue.
On some coaches, possibly earlier years, if the brake systems pressures are low THE AUX AIR SYSTEM AIR PRESSURE WILL NOT PRESSURIZE THE BRAKE SYSTEMS. Conversely, on some coaches, possibly later models, if the brake systems pressures are low THE AUX AIR SYSTEM AIR PRESSURES MAY PRESSURIZE THE BRAKE SYSTEMS. Why is this distinction important for an owner to know? It is important because it may affect a brake system check and provide an owner with a false sense of well being.
As owners of large vehicles with air brakes we have a responsibility to do a brake system check on our coaches as a part of a pre trip inspection. It is as important as checking lights and tire pressures. Part of the brake system check is to observe if there is any loss of air pressure when releasing the emergency brake or when applying the service brakes. But another component of the test is to time how quickly air system pressures are built up. If the aux air compressor will feed pressure to the brake system it may mask a brake pressure leak or may contribute air to pressure build up in concert with the engine driven compressor.
If your aux air compressor does supply air pressure to the brake systems MAKE SURE THE AUX COMPRESSOR IS OFF DURING A BRAKE CHECK.
While this may seem like minutia to fellow gear heads it is important for everyone to understand exactly how their coach air systems work because this could be a safety issue.
On some coaches, possibly earlier years, if the brake systems pressures are low THE AUX AIR SYSTEM AIR PRESSURE WILL NOT PRESSURIZE THE BRAKE SYSTEMS. Conversely, on some coaches, possibly later models, if the brake systems pressures are low THE AUX AIR SYSTEM AIR PRESSURES MAY PRESSURIZE THE BRAKE SYSTEMS. Why is this distinction important for an owner to know? It is important because it may affect a brake system check and provide an owner with a false sense of well being.
As owners of large vehicles with air brakes we have a responsibility to do a brake system check on our coaches as a part of a pre trip inspection. It is as important as checking lights and tire pressures. Part of the brake system check is to observe if there is any loss of air pressure when releasing the emergency brake or when applying the service brakes. But another component of the test is to time how quickly air system pressures are built up. If the aux air compressor will feed pressure to the brake system it may mask a brake pressure leak or may contribute air to pressure build up in concert with the engine driven compressor.
If your aux air compressor does supply air pressure to the brake systems MAKE SURE THE AUX COMPRESSOR IS OFF DURING A BRAKE CHECK.