Auxiliary Compressor Air Flow to Level on '01

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Auxiliary Compressor Air Flow to Level on '01

May 19, 2018, 10:30:47 am

For quite some time I thought that the "third" air tank on our 2001 U320 fed air directly to the air bags to level when in Park.

But I began to realize something more was going on as on one trip I carefully monitored air pressure in the two main (brake) tanks versus the third tank. I figured out that I had lost the function of the check valve and in doing that the auxiliary compressor was pressurizing the two main tanks and the third tank all at one time, a no-no.

Which led me to wonder, why is there even an air line from the aux compressor to the main tanks if it is not supposed to air up those two main tanks (on an '01)

So I visited one of the Foretravel design and electrical gurus, Aubrey Lee at MOT now. And this is the process.

The main air tanks are the air supply to maintain level when parked, it is not the third air tank function at that point as I thought. When/if the main tanks pressures drop below that air pressure for the park brake operation, which is about 70 psi, THEN the main tanks are replaced by the third tank to maintain level and the slide bladder. So until that time, the aux compressor would not operate (be needed).

In looking at the air line schematic, I believe I see that some air lines are used by the engine compressor and the auxiliary compressor to air the bags. In that, the line would allow the aux to try to pressurize the two main tanks but to avoid burning out the aux by it running that long trying to pressurize those tanks, check valves are to prohibit air flow from the aux into the main tanks and thus wet tank. In my episode I could see that the two main and third tanks were all pressurizing at once by the aux compressor (check valve failure). To protect the aux compressor, I limited the run time to about five minutes, let it cool and go again. [Or, just crank the engine and let the engine compressor pressurize the main tanks that the aux compressor would not try to feed those.]

I bet few care that this is so......but for the one or two people that might I am trying to explain how the system functions on the 01. Hope I have explained this properly, accurately....always learning.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #1 – May 19, 2018, 11:11:10 am

Quote from: Michael & Jackie – May 19, 2018, 10:30:47 am

For quite some time I thought that the "third" air tank on our 2001 U320 fed air directly to the air bags to level when in Park.

But I began to realize something more was going on as on one trip I carefully monitored air pressure in the two main (brake) tanks versus the third tank. I figured out that I had lost the function of the check valve and in doing that the auxiliary compressor was pressurizing the two main tanks and the third tank all at one time, a no-no.

Which led me to wonder, why is there even an air line from the aux compressor to the main tanks if it is not supposed to air up those two main tanks (on an '01)

So I visited one of the Foretravel design and electrical gurus, Aubrey Lee at MOT now. And this is the process.

The main air tanks are the air supply to maintain level when parked, it is not the third air tank function at that point as I thought. When/if the main tanks pressures drop below that air pressure for the park brake operation, which is about 70 psi, THEN the main tanks are replaced by the third tank to maintain level and the slide bladder. So until that time, the aux compressor would not operate (be needed).

In looking at the air line schematic, I believe I see that some air lines are used by the engine compressor and the auxiliary compressor to air the bags. In that, the line would allow the aux to try to pressurize the two main tanks but to avoid burning out the aux by it running that long trying to pressurize those tanks, check valves are to prohibit air flow from the aux into the main tanks and thus wet tank. In my episode I could see that the two main and third tanks were all pressurizing at once by the aux compressor (check valve failure). To protect the aux compressor, I limited the run time to about five minutes, let it cool and go again. [Or, just crank the engine and let the engine compressor pressurize the main tanks that the aux compressor would not try to feed those.]

I bet few care that this is so......but for the one or two people that might I am trying to explain how the system functions on the 01. Hope I have explained this properly, accurately....always learning.

Think you got it exactly right Mike. But for some reason on later years, [my 03 anyway] Foretravel installed a solenoid valve, with switch on side consul, in the discharge of the aux compressor that is piped directly to wet tank, so you can fill it to 90 psi with the aux comp. Don't know if my compressor is different, but it is rated continuous duty.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #2 – May 19, 2018, 11:47:46 am

Yes, your is better compressor. In NM one year I had a question and a fellow came in to help me, and asked....where is that switch?

What switch? He said beside joy stick area is or should be a switch to control that aux so I can turn it on to air the main tanks quietly in morning when leave park and not have to disturb neighbors with running engine a long time to pressurize the tanks.

When I got home I believe techs told me that became available sbout 02 and larger aux. maybe I remember that incorrectly though

Thanks Jim

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #3 – May 19, 2018, 12:50:44 pm

Still takes a while to go from 90 to 120 psi, so plumbed a Viair 450c into line to wet tank and used dash switch to control it. It has its own dryers and pressure switch [115 psi] with a valved crossover to aux comp system in case Thomas comp gives up.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #4 – May 19, 2018, 01:21:35 pm

In Mike's coach and mine we give up no basement floor space for compressors or hydraulic pumps. For some a distinct advantage.

In U320 coaches starting at build number 5920 In 2001 they used a significantly bigger compressor with an air dryer. If you ever need to replace your compressor on an earlier 2001 U320 build number consider the bigger one from later years.

The drawing number is B-2254

Different years and models may have different revision designations or maybe even a different drawing number.

Check the box labeled CN to see the effective build number.

On my coach I can hook up a compressor to the aux air line connection and level the coach but it does not charge the service tanks or the HWH tank.

Air in the service tanks comes from the engine compressor only on my coach (I think it is the same as Mike's). Air comes from those tanks through the safety valve (also called a pressure protection valve) to the leveling manifolds (lines 27 and 28 with an interconnecting line 50). When air pressure in those tanks falls below the safety valve (also called a pressure protection valve) level the safety valve (also called a pressure protecion valve) acts like a check valve and stops air from leaving the tanks. At this point if the leveling manifolds call for air the small compressor will come on supplying air through line 57.

I don't think the small compressor or the external air connection can push air backwards through the safety valves (also called a pressure protection valve) when they are closed or past the check valve in line 57 to the small HWH tank. Nor does the small compressor supply air to the external air connection.

I have air leaks, don't we all. But I know that from the bladder manifold to the bladder is air tight. Even after a few months the air pressure in the bladder never changes. My coach will stay level enough for a week or more with no adjustments. The air leaks that are there are a bit annoying but not worth that much time.

The attached drawing is for build numbers 5871-5919

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #5 – May 19, 2018, 04:00:19 pm

Roger wrote: Air in the service tanks comes from the engine compressor only on my coach (I think it is the same as Mike's). Air comes from those tanks through the safety valve to the leveling manifolds (lines 27 and 28 with an interconnecting line 50). When air pressure in those tanks falls below thw safety valve level the safety valve acts like a check valve and stops air from leaving the tanks. At this point if the leveling manifolds call for air the small compressor will come on supplying air through line 57.

Roger summarized it better than I....not a surprise there!

But ditto what Roger said....just to reiterate.....my aux is not designed or intended to pressurize the main two tanks, and it doing so was due to the check valve failure which I noticed by monitoring psi changes in all tanks. I could convert the system to a larger aux compressor but think fixing the check valves is best route for me given cost and lack of ability.

The reason for my post was to hopefully educate a few other owners of this series of coaches on the potential for this check valve failure and the possible consequence of doing so (burned up compressor).

Thanks all, as always.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #6 – May 19, 2018, 04:38:25 pm

My check valves were also leaking by. One reason I went to the second compressor separate from the aux compressor if I want to air up before leaving.
Might just be semantics, but a safety valve to me denotes protection from overpressure. In my schematic this valve is labeled "pressure protection valve"
Is this what you are referring to when you say safety valve?

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #7 – May 19, 2018, 07:09:48 pm

Semantics, I guess. I have herd them referred to either way. Some of us have motorhomes, some have a coach, some have a motor coach, some have a bus.

Technical Description
Pressure protection valves (PPV) or safety valves, what ever you call them insure that the air brakes, which are supplied from the primary reservoir, always have adequate pressure to function normally. This is a normally closed pressure sensing valve which allows air to flow freely in both directions as long as the upstream (primary) reservoir pressure is above the set point of the valve. Typical set points range from 55±5 psi to 85±5 psi. If a downstream failure occurs or during start up, the primary tank pressure may drop, thus causing the PPV outlet to shut off, in order to maintain the primary reservoir pressure.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #8 – May 19, 2018, 07:36:18 pm

Quote from: Roger & Susan in Home2 – May 19, 2018, 07:09:48 pm

Semantics, I guess. I have herd them referred to either way. Some of us have motorhomes, some have a coach, some have a motor coach, some have a bus.

Technical Description
Pressure protection valves (PPV) or safety valves, what ever you call them insure that the air brakes, which are supplied from the primary reservoir, always have adequate pressure to function normally. This is a normally closed pressure sensing valve which allows air to flow freely in both directions as long as the upstream (primary) reservoir pressure is above the set point of the valve. Typical set points range from 55±5 psi to 85±5 psi. If a downstream failure occurs or during start up, the primary tank pressure may drop, thus causing the PPV outlet to shut off, in order to maintain the primary reservoir pressure.

Thanks for the explanation. Problem being an engineer, I tend to rely on proper terminology and my schematics. Maybe OCD on my part.
Safety valve - Wikipedia
Pressure Protection Valve - Haldex product category

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #9 – June 18, 2018, 09:59:47 am

I hope continuing this thread allows me to bring up a variation on the questions and discussions I initiated, for I have a bit of a new slant.

Do you know what pressure you have set as a shutoff for the 2001 and older coaches, those before the "new" larger aux compressor?

MOT reset mine to 115 psi and I am not sure that is proper. Heretofore it has always come on at 64 and cut off at 85.

It has proved valuable more than once to know that it takes 3:30 minutes to bring the pressure back to 85. In doing this the compressor gets very hot. I am concerned that allowing it to go even higher, and thus much longer running times, will be just too much for it and I will lose the compressor. Perhaps the 115 is ok for the next generation, especially the 2002, coaches, but is that ok for my 01?

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #10 – June 18, 2018, 10:07:14 am

Mike, that seems a little high. I have an 03 with the bigger compressor, but my schematic still indicates cut in at 70 and cut out at 90 psi. Do not think you would need over 90 psi just for seals and leveling.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #11 – June 18, 2018, 10:12:10 am

I'm running a Thomas TA-4101DC with no problems, cut in at 60PSI and cut out at 80PSI.

It takes about 2 minutes to build pressure.

How hot is yours Mike?

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #12 – June 18, 2018, 12:13:36 pm

At 85 psi too hot to hold hand on top of compressor piston cylinder head

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #13 – June 18, 2018, 12:28:18 pm

Quote from: Michael & Jackie – June 18, 2018, 12:13:36 pm

At 85 psi too hot to hold hand on top of compressor piston cylinder head

Just bled mine down to 70 psi, shutoff in 2 min at 90 psi, head temp was 124 f.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #14 – June 18, 2018, 12:50:49 pm

Mike, the smaller compressor in the 2001 is rated for 100 psi. Probably better to set the cut out at 85-90 psi. The seals take 15 psi max. Adding air to rear air bags is probably the maximum it will do and 90 psi is sufficient for that.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #15 – June 18, 2018, 01:13:11 pm

My Gauges to level is 95psi .. will not go any higher even after I changed the compressor on the engine.. Internally set I believe..

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #16 – June 18, 2018, 07:09:27 pm

jcus, where did you get the air filtering system for the Maxair? Looks good.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #17 – June 18, 2018, 08:04:10 pm

Quote from: rbark – June 18, 2018, 07:09:27 pm

jcus, where did you get the air filtering system for the Maxair? Looks good.

https://www.amazon.com/PneumaticPlus-SAU2030M-N02G-Three-Drying-System/dp/B00OJX6CJ2/ref=sr_1_1?ie=UTF8&qid=1529366599&sr=8-1&keywords=PneumaticPlus+SAU2030M-N02G+Mini+Three+Stage+Air+Drying+System%2C+1%2F4%22+NPT+-+Particulate+Air+Filter%2C+Coalescing+Filter%2C+Air+Pressure+Regulator+Combo+-+Poly+Bowl%2C+Manual+Drain

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #18 – June 18, 2018, 08:31:53 pm

Jim C, after getting to 85 psi, I found 138 degrees on side of cylinder and 151 degrees on the top of the cylinder

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #19 – June 18, 2018, 08:55:28 pm

Quote from: Michael & Jackie – June 18, 2018, 08:31:53 pm

Jim C, after getting to 85 psi, I found 138 degrees on side of cylinder and 151 degrees on the top of the cylinder

Don't forget yours ran longer and mine is a little bit bigger so probably better heat dissipation.
Just drained my seal tank, 0-90 psi, 7 min, head temp 192 f.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #20 – June 18, 2018, 09:50:52 pm

Jim and Roger

Roger posted the B-2193 schematic for my 01 air HWH. You find it in his month ago post.

I am trying to follow it and do not see how the third tank supplies air to the HWH suspension system.

Line 57 out of the aux compressor seems to become, without using the third tank, the supply via line 27 to the rear manifold. I gather that if the Rear Brake Right tank can supply what the manifold needs, then line 57 is not used and the Rear Brake Tank supplies the needed air. Is that right?

If that is correct, then similarly it appears that line 50 become the supply, via air from line 57, to the front manifold, where line 50 actually changing to feed line 28 that goes on to the front manifold.

IF all that is true, what is the role of the "third" tank we have? It is more than seal as I understand it. And as I do not hear the 12 v aux compressor running to level the coach (when the L and R tanks are below 70 psi}, it seems without a doubt to take air from the third tank, and that seems what is verified by the pressure gauge on the third tank.)

---looking at the schematic, line 57 seems to go to a junction and in that way interconnects to and supplies lines 27 and 50. Is that the way to read this?

---further, it appears that a check valve or pressure protection valve (?) on each the two large keeps the aux compressor (line 57) from pressurizing the L and R tanks. Right?

And just to close the loop, line 8 (and then 7 from

from the Wet Tank (engine compressor) is the source of air to the L and R tanks on these model coaches. The aux compressor is not to be a secondary supply.

Roger....I must have this wrong. What is the scoop?

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #21 – June 19, 2018, 12:28:46 am

Mike, that is pretty much correct for a fairly small range of coaches, 5871 to 5919.

The check valve at the four way connection at the end of line 57 prevents air from line 57 from going into the rear tank. As long as the pressure in the Right (Rear) tank is above the low set point of the Protection Valve air from the Rear Tank will flow out of the tank to the four way connection. Line 61 goes to the retarder accumulator. Line 5 goes to the aux air connection. After the check valve line 27 goes to the rear leveling manifold. Line 50 goes to a four way connection. Line 55 goes to front ride height control valve. Line 28 goes to the front leveling manifold.

The arrow in the check valve symbol show the only way air will flow.

The only line that goes to the HWH tank is line 75 after a check valve. The HWH tank then goes to the slide manifold where pressure for the slide bladder comes from. It is also the air in this tank that providea the air flow to create a vacuum to deflate the bladder. As soon as air starts flowing out of the HWH tank and pressure drops below the low set point for the HWH compressor the HWH compressor comes on.

If you are parked and the pressure in the front and rear tanks is less than the low point for the protection valves then no air comes from these tanks when either leveling manifold calls for air to level the coach. Leveling is controlled by the automatic mode or manual mode using the HWH level computer. In this case the HWH compressor will come on and pressurize the leveling manifolds. No air from the HWH tank is used for leveling.

If you are driving then air to the front and rear tanks comes from the engine compressor via the wet tank. This air is used for braking and for leveling which is controlled by the ride height valves.

When you are parked the HWH leveling computer will always first try to let air out of the high side (or end) to achieve a level condition. If that is not enough then it will try to add air to the low side (or end) and if there is not enough preddure from the front and rear tanks then the compressor will come on.

When we are parked I level the coach while the engine is still running and the slide is out by adding air to the low end or side by using the manual buttons. Then the engine is shut off. The HWH compressor is shut off after it is done filling the HWH bladder tank. After a few days one side may be lower than the other and I will let some air out of the high side.

I can maintain satisfactory level and bladder seal pressure for a couple weeks or more this way. I have some leaks but I am not chasing them down.

If I am all all out of room to let air out to get level I hook up my 120 v compressor to the Aux Air connection (using a male to male connector) and raise the coach and adjust level. If we are on a level site then eventually we will be down to the stops and still level.

Clear as mud, right?

The confusing part of this is that it only applies to a small range of coaches, yours and mine included.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #22 – June 19, 2018, 12:55:54 am

MOT worked in two ways to address this....

Without being in level mode, the aux compressor was coming on (I did not know it)

I noticed the pressure in all three tanks being equal. What gives? So I dumped L and R to 60 psi, ran Third tank (aux) up to 85 psi.

In thirty minutes all tanks were about 70 psi and stay that way.

So....to me...the higher pressure Third bleeds into L and R. When all reach same pressure, they essentially quit adjusting except to whatever slow system leaks cause them to change.

My need....for me to give them an idea what is causing this. All I can think of is check valve related. But that on the surface makes no sense, for two would have to leak the same (one each on L and R). But that seems to suffer logically.....IF there is no tie between the Third Tank and the L and R, that does not work. But the schematic shows Third to connected to L and R. I doubt that is correct though for when parked in level the aux compressor does not have to run to level, it levels without noise of the aux. And at times it will run to build up pressure to the Third tank, not doing any leveling.

I will study what you wrote. I bet the answer is in there as to what needs fixing.

Thanks for your efforts. I will meet with Aubrey Lee tomorrow, discuss ideas.

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #23 – June 19, 2018, 01:18:31 am

Zthanks for this thread. Our coach is in that small range where this applies.

Believe I understand most of the explanations. I don't understand why the check valve in line 57 exists.

Early in our ownership had a failed pressure switch on the aux compressor, never ran. Engine compressor kept the slide bladder inflated, generated vacuum to deflate the slide bladder. Found the check valve in line 57 had failed and this let the engine compressor keep the slide bladder inflated and generate vacuum to deflate the bladder.

Replaced the check valve and lost the ability for the engine compressor to serve as backup to the aux compressor. Replaced the check valve with a quarter turn valve that I left open. Once again, had the engine compresor as backup.

On a later visit to HWH, asked them about the line 57 check valve. They said it's not from them, an addition from Foretravel. This concerned me so I switched the quarter turn valve back to a check valve.

Any reason not to dump the check valve in line 57? I don't see why it exists.

Thanks

Re: Auxiliary Compressor Air Flow to Level on '01

Reply #24 – June 19, 2018, 01:30:06 am

aha there is a way though....if the check valve on line 15 fails, then air in the third tank can flow backwards out of the tank into the system and away from the seal use. That would give a supply to the L and R tanks even when the aux is not running,

But that would require another alignment,.....that the check valves on L and R be fouled and allow air to flow back into them, namely the air from the Third tank if its valve stuck open.

And if that is so, it would also explain why/how running the aux compressor would add air directly to the L and R tanks even if the line 15 valve was working correctly to seal off back flow from the Third. It seems unlikely that is the case as the L and R tanks do not seem to be gaining air as the aux is running but that might be just because their volumes are so large compared to the aux output that it is experienced over the course of a longer period to time

thinking. maybe Aubrey is the key unless I get there by applying later today the information you provided. and maybe in that is an experiment I can run....hmmm. Fascinating.

mike

P.S. Mike, I asked Aubrey something like that when I first had it in two weeks ago, will revisit. I asked him why not just leave out the complexities of line 57. His answer was that lines serve several purposes, the check valves allow doing that versus dedicated lines.

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