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Old 06-04-2016, 03:42 PM   #1
Mini-Skoolie
 
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low air pressure due to regulator dumping air

Hi. The air pressure is around 90psi and I can hear it dumping air pressure at this pretty low level. Is the air pressure regulator adjustable or is it a sign that it needs replacement or could some contamination in the air line be causing this? I am away from home now so am worried if pressure will continue to get lower... thanks!
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Old 06-04-2016, 03:48 PM   #2
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when you say regulator.. which part are you referring to? the pressure "regulator" or Governor is located right at the comrpessor itself.. it should not be dumping air there.. it turns the compressor on and off..

if you are under the bus and its the large round "Bendix" canister thats your Air Dryer.. and it sounds like the purge valve may be stuck if its constantly hissing air from the center of the device.. ...

90 PSI is when the governor should send air back to the dryer after a purge cycle occurs.. if the purge valve sticks the air gets dumped there and wont build up to the tanks..

Just need to know which part is dumping air and we can try to figure it out..

-Christopher
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Old 06-04-2016, 03:49 PM   #3
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also absolutelty DONT DRIVE it if your pressure is lowering... if you hit 60 PSI your spring brakes will begin to apply and will begin dragging trying to slow the bus down... if you get between 25 - 40 PSI the parking brake will pop out and imnstantly lock your rear wheels..
-Christopher
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Old 06-04-2016, 03:53 PM   #4
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most air governors are set at 120psi. they can be adjusted some, but not by accident.

Crawl underneath and get a spray bottle with soapy water and start looking for leaks.

an air governor is a cheap enough part to replace, thats a good place to start on your fix. especially if that is what is dumping your air.

find out where the air is coming from.
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Old 06-04-2016, 04:06 PM   #5
Mini-Skoolie
 
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Thanks for the info. It sounds just like before when I think the regulator or governor would periodically dump air when the pressure was above 120psi or so. It doesn't seem like anything is leaking, just that the regulator or governor is dumping air every few min at 90psi or so...
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Old 06-04-2016, 04:41 PM   #6
Mini-Skoolie
 
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OK I see the air dryer and the air is not coming from there. I see the air governor a few feet further back and no air from there either. I can hear and feel the air bleeding off every min or so from a brass fitting from the rear left air tank right behind the wheel. There is wire running to this also. Is this some sort of pressure switch? I am not sure if the issue is from the electric signal sent to it or something wrong with it mechanically? Seems like if I push in the inner thing of this brass fitting then the air pressure will build up to higher. Suggestions of the issue or fix? Thanks!
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Old 06-04-2016, 05:15 PM   #7
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take a picture of it.. sounds like a high pressure pop-off or possibly was an air-accessory hooked up at one time..

if you shut the bus off does the brass fitting bleed air down to about 60 and stop?

-Christopher
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Old 06-04-2016, 05:23 PM   #8
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Quote:
Originally Posted by engelstad View Post
OK I see the air dryer and the air is not coming from there. I see the air governor a few feet further back and no air from there either. I can hear and feel the air bleeding off every min or so from a brass fitting from the rear left air tank right behind the wheel. There is wire running to this also. Is this some sort of pressure switch? I am not sure if the issue is from the electric signal sent to it or something wrong with it mechanically? Seems like if I push in the inner thing of this brass fitting then the air pressure will build up to higher. Suggestions of the issue or fix? Thanks!
the air governor is normall attached directly to the compressor itself.. I put my bus away or id show you a pic of mine.. here is a link to one online..

D2 Truck Air Governor Bendix Midland Freightliner - Newegg.com

there is also a protection valve between any main air and any accessories.. like air-ride suspension.., air seat, etc.. a protection valve makes sure the brake system is at 65 or above before it lets air go to the accessory...

protection valves look sort of like this.. and there may be more than one..



-Christopher
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Old 06-04-2016, 07:34 PM   #9
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Quote:
Originally Posted by engelstad View Post
OK I see the air dryer and the air is not coming from there. I see the air governor a few feet further back and no air from there either. I can hear and feel the air bleeding off every min or so from a brass fitting from the rear left air tank right behind the wheel. There is wire running to this also. Is this some sort of pressure switch? I am not sure if the issue is from the electric signal sent to it or something wrong with it mechanically? Seems like if I push in the inner thing of this brass fitting then the air pressure will build up to higher. Suggestions of the issue or fix? Thanks!
That sounds like a purge valve, it's probably on what's commonly known as the "wet" tank, it's task is to periodically let a little air out, draining moisture with it. Over time, these can get gummed up and stick open. The wire is from a computer/timer telling it to open (probably every few minutes to half-hour or so.) Shouldn't be expensive to replace. You *could* replace it with a brass plug as a temporary fix, but remember to occasionally drain the air tank if you do so (at least once a day, usually at the end of driving.)
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Old 06-04-2016, 07:46 PM   #10
Mini-Skoolie
 
Join Date: Sep 2015
Location: Albuquerque, NM
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Year: 1998
Coachwork: Blue Bird
Chassis: TC2000 RE
Engine: Cummins 8.3; Allison 3060R
Rated Cap: 66 passenger
Ok, I turned off bus and the air release to reduce pressure when bus is turned off, does not come from the brass fitting that seems to release air a few times per minute when driving.

Also I put my finger on it for a few min to see if air pressure would build up and gauge didn't show pressure increase. When I took my finger off of it though the pressure did decrease. I am in rural Nebraska but I found auto parts store and replaced the air dryer. No change noted yet but barely drove it since then. Old air dryer was very gunked up though.

If the brass thing is dumping air, I was wondering if I could remove the wire going to it, but it doesn't seem to be connected with quick disconnect... ??
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