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Both air tanks lose air together


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Search of lots of posts on air loss with no definitive answer.

Air brake test works as it should and there is no problem while driving as the compressor keeps the guages at 100 plus pounds.

On our 2004 Dynasty after parking and leveling, both tanks will drop simultaneously to about 30 pounds after about 3 or 4 hours. The coach will stay level without the auxillary compressor running so the air bags are not losing air

I have sprayed soapy water on every fitting on  both tanks, all three 6 packs, and the air dryer and see no leaks.

Any suggestions on what might be a common point on both tanks that might be causing both tanks to leak at the same speed?

Is there a way to insert a dye to possibly locate the leak?

Thanks in advance for any suggestions.

Mike 

Edited by bmulvenna@hotmail.com
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Mike, one possibility: the tanks are connected through a shuttle valve, the valves plunger will move towards the leaking side and isolate them in case of a severe leak but a very small leak may not be enough to close the passage or the valve isn't closing tightly enough. I had, still have that situation eventhough it takes a week now to drain down to 60 psi, the PPV pressure. The way I found out where the leak is, I removed the connecting rear line at the shuttle valve up front and capped both sides. That let me confirm a slow leak in the the front plumbing, one of the numerous accessories past PPV. I'll see if I have a picture of my disassembled valve, there's just a cylinder inside that moves with airflow and closes the leaky side.

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Don't know how common it is, but my original Meritor / Wabco System Saver air dryer's regeneration valve would open and release tank air pressure off and on, hours after shutting down the engine!

Noticed it while under the coach draining oil, hour or so after shutdown!

Replaced the dryer and all's been fine since!

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43 minutes ago, bmulvenna@hotmail.com said:

Search of lots of posts on air loss with no definitive answer.

Air brake test works as it should and there is no problem while driving as the compressor keeps the guages at 100 plus pounds.

On our 2004 Dynasty after parking and leveling, both tanks will drop simultaneously to about 30 pounds after about 3 or 4 hours. The coach will stay level without the auxillary compressor running so the air bags are not losing air

I have sprayed soapy water on every fitting on  both tanks, all three 6 packs, and the air dryer and see no leaks.

Any suggestions on what might be a common point on both tanks that might be causing both tanks to leak at the same speed?

Is there a way to insert a dye to possibly locate the leak?

Thanks in advance for any suggestions.

Mike 

I have the exact same problem including the timing. I have been looking for the leak for over three years and still no joy.

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20 minutes ago, Ivan K said:

Mike, one possibility: the tanks are connected through a shuttle valve, the valves plunger will move towards the leaking side and isolate them in case of a severe leak but a very small leak may not be enough to close the passage or the valve isn't closing tightly enough. I had, still have that situation eventhough it takes a week now to drain down to 60 psi, the PPV pressure. The way I found out where the leak is, I removed the connecting rear line at the shuttle valve up front and capped both sides. That let me confirm a slow leak in the the front plumbing, one of the numerous accessories past PPV. I'll see if I have a picture of my disassembled valve, there's just a cylinder inside that moves with airflow and closes the leaky side.

Ivan is correct.  This valve connects the rear main dry air tank to the front dry aux air tank.  This valve enables the drive axle spring brakes to be released by air in either dry air tank.  This air valve also balances air between the two tanks but will close if the air leak is fast enough.  The valve should be on your front aux dry air tank.

Screenshot_20240628-144007~2.png

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42 minutes ago, bmulvenna@hotmail.com said:

Search of lots of posts on air loss with no definitive answer.

Air brake test works as it should and there is no problem while driving as the compressor keeps the guages at 100 plus pounds.

On our 2004 Dynasty after parking and leveling, both tanks will drop simultaneously to about 30 pounds after about 3 or 4 hours. The coach will stay level without the auxillary compressor running so the air bags are not losing air

I have sprayed soapy water on every fitting on  both tanks, all three 6 packs, and the air dryer and see no leaks.

Any suggestions on what might be a common point on both tanks that might be causing both tanks to leak at the same speed?

Is there a way to insert a dye to possibly locate the leak?

Thanks in advance for any suggestions.

Mike 

TYPICALLY, so one has a benchmark or yardstick.  MOST Monaco’s “loose” air.  The rate is the key.  Frank’s 08 Dynasty has a different system than my Camelot.  Ben and I have one combo Tank.  Dynasty, generically” has two separate tanks.  We both will drop to ZERO over a period of time.  For you to evaluate if your system is normal, here is how mine drops and, I think, Frank’s is similar.  In warm weather, I can usually keep pressure for 4 - 5 days….but my yardstick….totally drained.  So that is my rule of thumb.

NOW if you are losing 70 odd PSI in 4 hours, you have an issue.  The Monaco warranty rule, IIRC, was 24 hours….so, the rate was about 4 PSI/Hour.  You are about 18 - 20 PSI/Hour.

I never see, as does Frank, the MH list or sag or drop….snd that is for months….always level,

I did my leak testing.  My biggest was the DRYER.  The dryer has two sections….Front and rear. It was more cost effective to buy a new one, discounted, than to pay my OTR shop to rebuild mine. SO…don’t overlook it.  My gut says you have a “fitting” issue and the fitting needs to be taken apart and a short amount cut off and then reassembled.  Have you tested or leak or soap tested the canisters.  That leak rate will lock the brakes…

Can’t provide you with more direction….except to quantify and say….Monaco would fix under warranty and it is at least 2X their standard.

 

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Don't forget to check the tag axle regulator, the tank drain valves, the air step regulator, the air horn solenoid, the parking brake, and the air pressure sensors for brake lights and low air for leaks.   My last few leeks were the parking brake, air tank drain valve, and the tag regulator.

 

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5 hours ago, Tom Cherry said:

  Frank’s 08 Dynasty has a different system than my Camelot.  Ben and I have one combo Tank.  Dynasty, generically” has two separate tanks.   

 

Don't know about yours, but I have two separate tanks, one being a split tank.

The split tank is half supply tank (wet tank), the other half is primary dry tank. The secondary dry tank is a full tank.

Don't think the Dynasty has anything different other than maybe the location of the tanks.  Frank will correct me if his Dyn has separate supply tank and primary dry tank. 

Edited by 96 EVO
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Posted (edited)

Found a leak in the air dryer. Will order a new one. Not sure if this is the total solution but will find out.

I again checked for leaks in all fittings on both front and rear tank, door seal, air horn, park brake, dash guages, all 3 6 packs, tag pressure, govenor, drain valves, step, brakes, air bags, etc and found no leaks. Only the leak in the dryer. Will report back if new dryer fixed the issue.

Thanks for all the suggestions.

Mike

Edited by bmulvenna@hotmail.com
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2 hours ago, bmulvenna@hotmail.com said:

Found a leak in the air dryer. Will order a new one. Not sure if this is the total solution but will find out.

I again checked for leaks in all fittings on both front and rear tank, door seal, air horn, park brake, dash guages, all 3 6 packs, tag pressure, govenor, drain valves, step, brakes, air bags, etc and found no leaks. Only the leak in the dryer. Will report back if new dryer fixed the issue.

Thanks for all the suggestions.

Mike

Like the proverbial pachyderm….one common sense bite at a time….

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First time posting, Hope its ok to jump on someone else's post... my suspension air bags stay up for days but the tank for my air brakes leak down from 110 lb to 50 lb within minutes. Like if I stop to refuel I have to wait a minute to air up before I can leave the pumps. Very inconvenient and Im sure my compressor is running more than it should.

When Im under my Crown Royale (92) after its shut off, I can hear an intermittent 'moaning' noise coming from the tank on the front passenger side. Getting as close as I can and feeling the different valves it feels like a fitting on the top of the tank is 'moaning'/vibrating ever so slightly as it releases air.

Where do those valves route to? Is there a way to test them besides a bubble test because its very hard to see up there?

If I was guessing it sounds like some kind of check valve thats not holding. Is there a check valve on top of the tank?

Edited by GoWestMan
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3 hours ago, GoWestMan said:

First time posting, Hope its ok to jump on someone else's post... my suspension air bags stay up for days but the tank for my air brakes leak down from 110 lb to 50 lb within minutes. Like if I stop to refuel I have to wait a minute to air up before I can leave the pumps. Very inconvenient and Im sure my compressor is running more than it should.

When Im under my Crown Royale (92) after its shut off, I can hear an intermittent 'moaning' noise coming from the tank on the front passenger side. Getting as close as I can and feeling the different valves it feels like a fitting on the top of the tank is 'moaning'/vibrating ever so slightly as it releases air.

Where do those valves route to? Is there a way to test them besides a bubble test because its very hard to see up there?

If I was guessing it sounds like some kind of check valve thats not holding. Is there a check valve on top of the tank?

Unless one is “qualified” or cerified to performce the DOT required Air System tests and such, I’d find a good OTR truck shop and say…leaking….fix it.  The leak rate you quoted, unless I misunderstood, would FAIL….miserably, the AIR BRAKE TEST.

This is the USDOT Air Brake pretrip or performance test, in simple and easy to perform steps.  If it fails….then figure out HOW to fix it or have a professional fix it.  Driving it if it failed can  be deadly…

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3 hours ago, GoWestMan said:

 

If I was guessing it sounds like some kind of check valve thats not holding. Is there a check valve on top of the tank?

Are you saying you can feel the air coming out of this valve? It could simply be a failing pressure relief valve!

It's really hard to diagnose, without seeing it! There's several different types of valves and fittings on each of your tanks!

 

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Doug, does the suspect 'moaning' fitting has a line coming out of it? If you are talking about passenger half of the front tank, I would expect 2 lines going back from the top. The big one from drier, small one to governor. I have one more but that's optional from air leveling compressor.  You should be able to take a phone picture of it too but the leak isn't necessarily there, it could be at the other end of the line.

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5 hours ago, Tom Cherry said:

Unless one is “qualified” or cerified to performce the DOT required Air System tests and such, I’d find a good OTR truck shop and say…leaking….fix it.  The leak rate you quoted, unless I misunderstood, would FAIL….miserably, the AIR BRAKE TEST.

This is the USDOT Air Brake pretrip or performance test, in simple and easy to perform steps.  If it fails….then figure out HOW to fix it or have a professional fix it.  Driving it if it failed can  be deadly…

I don't see anything there it wouldn't pass. It only leaks down with the engine off. It maintains pressure at 100 psi when running. Test says 120 to 135 psi but it's never been up that high even before the leak. And it has a new compressor and was set by a semi shop and a 60 yr old mechanic who specializes in Cummins powered RVs.

Edited by GoWestMan
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20 minutes ago, GoWestMan said:

I don't see anything there it wouldn't pass. It only leaks down with the engine off. It maintains pressure at 100 psi when running.

Maintaining 100 psi when running is NOT a test used to pass an air leak test.  You must measure the PSI pressure drop over time with the engine OFF.  After airing up shut off the engine and see if you lose more that 2 PSI/minute.  If you do, your system has failed a DOT air brake test.

To lose 60 psi and still pass would take over 30 minutes.  You said it takes just a few minutes to lose 60 psi - that would be a FAIL.

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4 hours ago, Ivan K said:

Doug, does the suspect 'moaning' fitting has a line coming out of it? 

Answer to this question will tell us a little more!

1 hour ago, GoWestMan said:

I don't see anything there it wouldn't pass. It only leaks down with the engine off. It maintains pressure at 100 psi when running. Test says 120 to 135 psi but it's never been up that high even before the leak. And it has a new compressor and was set by a semi shop and a 60 yr old mechanic who specializes in Cummins powered RVs.

If it continues to lose air at that rate, it's going to need another new compressor before long!

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1 hour ago, Ivan K said:

I had to demonstrate the air system test with engine off but ignition ON so ride hight and air accessories are functional and potentialy leaking too.

Demonstrate to whom? Maybe its different here but we have an initial inspection when you bring in an RV from out of the province (bought it in California, drove it back to Alberta) but after that, as long as it stays insured, there are no more inspections til you sell it to someone else.

1 hour ago, 96 EVO said:

Answer to this question will tell us a little more!

If it continues to lose air at that rate, it's going to need another new compressor before long!

Yes it has a line coming out of it. I think its the fitting furthest to the front of the RV.

6 hours ago, Ivan K said:

Doug, does the suspect 'moaning' fitting has a line coming out of it? If you are talking about passenger half of the front tank, I would expect 2 lines going back from the top. The big one from drier, small one to governor. I have one more but that's optional from air leveling compressor.  You should be able to take a phone picture of it too but the leak isn't necessarily there, it could be at the other end of the line.

Yes it has a line coming out of it. Im pretty sure the leak is at this end as I can feel the fitting subtly vibrating when it 'moans'. I dont think it would transmit that far through rubber air lines and still vibrate...but maybe. Im not in it for a few days but Ill try to snap a pic when Im back.

7 hours ago, 96 EVO said:

Are you saying you can feel the air coming out of this valve? It could simply be a failing pressure relief valve!

It's really hard to diagnose, without seeing it! There's several different types of valves and fittings on each of your tanks!

 

No I cant feel air coming out. Only a subtle vibration. And yeah there are quite a few valves and fittings thats why its kinda hard to pinpoint which one is the culprit. I even tried using a mechanic's stethoscope but its really an awkward location at the top of the tank.

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Your likely going to need to follow that line and see where it comes from/ goes to.

You can check the downloads on this forum to see if there is a air schematic for a '92 Sig that may help, if it's available.

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Doug,

You need to follow the pre trip test that Frank posted l. I had problems similar to yours, but had never actually performed the test.  I ended up having a bad shuttle valve, several bad brake hoses, and I don’t know what else.  I never tested the brakes with the engine off before that.  Same thing with draining the tanks - I hardly ever did that because the air leaked out after a few hours and I figured there was no need.  I learned a lot!

 

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On 6/30/2024 at 10:02 PM, GoWestMan said:

Demonstrate to whom? Maybe its different here but we have an initial inspection when you bring in an RV from out of the province (bought it in California, drove it back to Alberta) but after that, as long as it stays insured, there are no more inspections til you sell it to someone else.

Yes it has a line coming out of it. I think its the fitting furthest to the front of the RV.

Yes it has a line coming out of it. Im pretty sure the leak is at this end as I can feel the fitting subtly vibrating when it 'moans'. I dont think it would transmit that far through rubber air lines and still vibrate...but maybe. Im not in it for a few days but Ill try to snap a pic when Im back.

No I cant feel air coming out. Only a subtle vibration. And yeah there are quite a few valves and fittings thats why its kinda hard to pinpoint which one is the culprit. I even tried using a mechanic's stethoscope but its really an awkward location at the top of the tank.

Doug, from what you are saying, the duty cycle of your air compressor is 100%. You already replaced the compressor once and with this duty cycle, you'll be replacing it again soon.

I can't stress enough that if you are not able to perform and pass an air brake pre-trip safety check and you are not able to find the leak(s), then your best solution is to find a truck repair shop to perform an air brake pre-trip safety check and repair the leak(s) in your air brakes.

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