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Both front and rear break air tanks losing pressure faster than normal

May 25, 2016, 09:56:28 pm

What would cause both break tanks to lose pressure faster than normal at about the same rate?

Original problem was the rear brake air tank lost pressure while driving. Took about 3 minutes for pressure to drop to the threashold point where it would then be pumped up again.  Several years ago I had the air dryer blow it's powder and over time I have had to replace failing fittings.

Now, after replacing the incoming one way valves on both tanks (figured if one was failing, the other might be in trouble soon) the rear tank no longer loses pressure quickly but now both tanks lose pressure at about the same slow rate - about 5 lbs in 3 minutes while driving. This is faster than it had been allowing for normal break and suspension air usage.

I confirmed both inlet one way valves are working by pumping up the tanks, opening the wet tank drain valve and not losing break tank pressure.  Also as part of fix for rear tank, all 3 tanks were blown out.  Lots of white dust.

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #1 – May 25, 2016, 11:15:19 pm

Larry,

Your coach is much newer than mine, so hard to make specific suggestions.  You have verified proper operation of the inlet check valves on front and rear tanks, so you know you are not losing air pressure "backwards" out of those tanks.  You have to be leaking somewhere downstream of the tanks.  Unfortunately, that includes most of the air operated devices on the coach.  Since both gauges go down together, I would concentrate on any lines that are common to both tanks.  On my air schematic this would, for instance, rule out the HWH leveling system (6-packs, air bags).

I would concentrate your investigation on the braking system (brake treadle valve, parking brake valve, control valves, relay valves, etc.)  On my coach, these items are serviced by common lines off both tanks.  You may have other devices on your coach that also tap into both tanks.

You already know you have the "white powder" circulating in your air system, so it may take a long time to eliminate all leaks.

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #2 – May 26, 2016, 09:11:26 am

Thanks. This is my thinking.  I guess I am looking for the silver bullet. 

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #3 – May 26, 2016, 10:01:34 am

Larry,

Below are links to three threads posted by Forum member Jim McNeece.  You will see that he did a terrific job of documenting his long fight to clean the white powder out of his (2003 U320) air system.  I am hoping you may benefit from his experience, and perhaps get a clue what to do next.  You could even try contacting Jim via PM - see if he has any additional advice.  Good luck with your project.


Desiccant powder in air system - anybody else with this experience?

2003 U320 - Phase 2 of Desiccant Powder Cleanup Complete

2003 U320 - Phase 3 of Desiccant Powder Cleanup

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #4 – May 26, 2016, 11:49:47 am

Quote from: Larry Rubin – May 25, 2016, 09:56:28 pm

Lots of white dust.

When is the last time your Haldex dryer was serviced?

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #5 – May 26, 2016, 05:06:55 pm

Thanks again for all the info.    I had the dryer serviced last November.    The powder is left over from several years ago. 

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #6 – May 27, 2016, 02:54:43 pm

I guess I'm just not a purist.  We can spend our lives chasing small air leaks which are far from threatening operational safety.  Engine compressor cycling every 20 minutes just wouldn't bother me.

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #7 – May 27, 2016, 04:16:08 pm

I would point out the leak down test is not done driving. While driving your air suspension is at the mercy of the roads.  With each bump they expel air and the tanks go down. Here in California on our terrible roads your cycle could be once a minute.  on smooth roads it could be once every 5 minutes.  go on line and see what the leak down test is  with out moving vehicle.

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Reply #8 – May 27, 2016, 05:05:00 pm

Leak down Rates

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Re: Both front and rear break air tanks losing pressure faster than normal

Reply #9 – May 27, 2016, 06:18:42 pm

Larry, took over a year, and reported in the Forum, for us to get smart and simply remove the wet tank!  Anyone recalls that report  will remember that MOT took it off the coach, took into the shop and blew compressed air in.....and the resultant exhausting of dust made a white dust storm in the shop!  Way more than expected.  ( had first tried a solution of cleaner with tank in place).

I really cannot tell you why I or someone did not just replace the wet tank at first...not expensive....or at least take it off.... when we saw evidence of these problems.  For over the course of the year, the dust ruined check valves, regulators and all manner of important parts.  Could not keep level without constant hassle.

Since getting that all done, we can let the coach sit for up to four weeks and the air in the two front tanks will hold at 65 psi and on the highway.  And with a fairly smooth ride, the compressor will cycle in 3 minutes versus the 7 it had come to due to failed parts.

Good luck.....call if think I can help talk more what it took to get that fixed.  But you have other issues too, I only commenting on the dust.  The bad bad dust!

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