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Old 10-03-2014, 11:29 PM   #11
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Originally Posted by rgmiller32 View Post
If it only does it while moving and you have air ride suspension. It could be from the bags dumping and refilling as you hit bumps and dips in the road. This will use air and cause the compressor to kick in. When sitting still there is no dumping and refilling.

Sounds 100% like my symptoms..... My air usage has nothing to do with speed or anything like that, just the fact of moving or not moving which makes sense that the bags are utilizing more air while driving down the road to keep the motorhome level...


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Old 10-08-2014, 08:14 PM   #12
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The compressor should not cut in if the pressure is between 100 and 130 lbs. Once.the pressure drops below 100 the compressor will cut in and bring the system back up to high pressure cutoff at 130 lbs. When this happens you should hear air vent
.... just like on a city bus

All air brake systems are the sames although the absolute pressure will vary.
Actually it works like this: The compressor runs CONTINOUSLY, always increasing the pressure in the tanks. That is, the compressor is a DIRECT DRIVE to the engine; there is no "clutch". To keep the tanks from exploding, a device referred to as a "governor" releases EXCESS pressure every couple of minutes.

The governor "popping off" is the sound you are hearing. It will release (as needed) whether you are moving, in park, stopped at a light, stepping on the brake, NOT stepping on the brake, whatever. The ONLY thing necessary for the governor to release every two minutes or so, is that the engine be running.

Think of it as similar to your wife's pressure cooker as it sits on top of the stove. When the pressure gets to high, the safety valve will open temporarily to release SOME of the pressure, then close to start the cycle again.

I rarely look at my pressure gauges. You have two of them because you really have (at least some) brake system parts "duplexed" for safety. Just like you car has two separate (and isolated from each other) brake systems for the front and rear axles.

If your pressure ever drops below around 75 lbs you'll get an audible alert. If you choose to ignore THAT, then at around 40 lbs, the yellow knob will automatically pop out, effectively applying your parking brake for you, whether you like it or not!!!

You can test this by stopping the engine, leave the parking brake off and then (while on level ground) repeatedly "pump" the brake pedal to deplete the pressure in the tanks. At around 40 lbs, the parking brake will set itself.

FWIW, a commercial drivers license test requires that you demonstrate your knowledge of this air brake feature, as well as quite a bit of other info about the air brakes. Even though it's rarely done in "real life", part of a standard pre-trip inspection on an 18 wheeler (required by law) is a brake test that takes about 2-3 minutes to complete and checks for SEVERAL brake related functions.

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Old 10-14-2014, 10:39 AM   #13
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Pretty sure my right rear air bag is leaking now. I know it's normal when they are full and the coach is off and you walk out you here the bags release some air but my rear one is constantly making the nous of air coming out. If I rock the coach by hand I hear it more, then stops and starts again on its own.... Looks like a trip to the local FL coming hot.....

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Old 10-14-2014, 06:31 PM   #14
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Good info there BooWho. That should be a stickie, if they have stickies here.
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Old 10-14-2014, 10:01 PM   #15
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PDF of Berkshire Airbrake System

This PDF of the Berkshire Airbrake system may help the discussion
Attached Files
File Type: pdf Air Brake System.pdf (164.8 KB, 79 views)
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Old 10-15-2014, 07:43 AM   #16
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booho you are close in your explanation of the air compressor system but here is maybe a better one. Although the air compressor is direct drive it has an unloader valve in it to keep it from building pressure. When your air system reaches 130 psi or so the governor senses that pressure from the tank and opens sending air to the unloader valve and moves the unloader to stop the build up of air also at the same time it sends air to the purge valve that is in the air dryer and it is designed to open and close once to purge any excess water out of the dryer. this is the whoosh you hear when your system is at full air pressure. When either of your gauges drop to around 100 psi or so the governor moves back exhausting the air pressure on the unloader valve starting the process all over. If you are hearing the whoosh of air repeatedly without a drop in air pressure you have a problem in this system that could cause premature wear on your air compressor.
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Old 10-16-2014, 06:51 PM   #17
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booho you are close in your explanation of the air compressor system but here is maybe a better one. Although the air compressor is direct drive it has an unloader valve in it to keep it from building pressure. When your air system reaches 130 psi or so the governor senses that pressure from the tank and opens sending air to the unloader valve and moves the unloader to stop the build up of air also at the same time it sends air to the purge valve that is in the air dryer and it is designed to open and close once to purge any excess water out of the dryer. this is the whoosh you hear when your system is at full air pressure. When either of your gauges drop to around 100 psi or so the governor moves back exhausting the air pressure on the unloader valve starting the process all over. If you are hearing the whoosh of air repeatedly without a drop in air pressure you have a problem in this system that could cause premature wear on your air compressor.
Thank you for the additional (and even more detailed than mine) explanation. I suspect you drove a lot longer than I, or that you worked for an AB manufacturer (or some such). Cajun, glad I could get at least partly correct info out.



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Old 10-16-2014, 06:55 PM   #18
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This PDF of the Berkshire Airbrake system may help the discussion
Outstanding document. Thanks for sharing.

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Old 10-16-2014, 08:53 PM   #19
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30 years bending wrenches on class 8 and heavy construction equipment cant sit in the seat long enough to be a driver
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Old 10-21-2014, 12:33 PM   #20
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Took the coach to a Freightliner service shop this morning and they found the leveling valve to be bad. Part should be here in a day or two. My coach just went past a year old but looking into the Freightliner warranty, looks like it is a 3 year/50,000 mile warranty so I should be covered.
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