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Topic: Pressure relief valve on auxilary air compressor is popping off every 2 seconds (Read 1094 times) previous topic - next topic

Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Hello,

We've been parked for about five weeks.  Two days ago we moved to different site in the same park.  After the engine had been running for a couple of minutes, a "popping/knocking" sound started.  It was the pressure relief valve on the aux compressor.  See photo at bottom of post (couldn't figure out how to put the photo after this paragraph.).

I discovered it starts happening when the air pressure gauges on the dash indicate 108 psi for both tanks.  If I repeatedly apply the brakes and keep the pressure below 108, the valve doesn't open.  As soon as the dash gauges say 108 psi, the valve starts opening about every two seconds.  If I let the pressure continue to build, it goes up to 123 psi or so (don't remember exactly).  The "popping" frequency remains at about every two seconds.  The aux compressor was not running.

After we parked, the levelling system seemed to operate fine.  Before and after the incident, the aux air compressor turns on about once a day and runs for about 20 seconds.  The relief valve doesn't open when the aux air compressor is running, only when the engine is running.  This was the first time this "popping" happened.

Any ideas on how to figure out what is wrong?

Thank you - Joe
2008 Nimbus

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #1 –
Joe,

Your HWH system is quite a bit newer than ours, but they all operate in a similar manner.  If you look at your air system diagram, you will see that the point where the aux compressor ties into the main air system is probably protected by a one-way check valve.  This valve allows the aux compressor to pump pressure into the main system, but does not allow main system pressure to flow backwards toward the pump.  There is also another check valve (#4 on the diagram below) at the pump.  My guess is that both of these check valves are not operating properly, and the pressure relief valve at the aux pump is "seeing" main system air pressure.

Under these conditions, the aux pump would still work fine when the big engine is off.  The only time you would notice the malfunction would be when main air system pressure exceeded the pressure rating on the aux pump safety relief valve.  The relief valve should be stamped with the pressure at which it should open.

I would recommend removing and inspecting both check valves.  Often these can be cleaned out and returned to service.  If the seats are worn, damaged or corroded, then the valves should be replaced.  You should also take a look at the normally closed pressure switch (#1 on the diagram below), since it may also be leaking.

Below is the diagram for the aux pump on our coach (HWH 600 Series).  Your setup may be different.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #2 –
It looks to me like the pressure relief valve in the picture is between the aux compressor and the water separator and then a check valve. I don't think pressure from the main compressor should be getting back to the relief valve if the check valve is working properly.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #3 –
I see 2 hoses being fed, T's and adapters, where's the check valve...?
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #4 –
See the drawing in Post#1.  Check valve is between the water separator bowl and the T. 
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #5 –
I see it now, not just a double nipple adapter like the other side of the water separator.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #6 –
Thanks for the input.  I have attached another photo that shows a bit more of the surrounding area and includes a second check valve.  Have also attached the drawings for the air and elec. connections.

Assuming both check valves are not working correctly, how/where do I shut off air to the aux compressor?  Please note, our setup only has connections to port A (HWH Air Leveling System) and C (Air Seal/Acc. Air Tank).  Port B ("Coach Air Supply System") is plugged.  I don't have any documentation on the air system other than the HWH system, nothing regarding the brake system, the main compressor etc.

If there are no valves to isolate the aux pump, what is the proper procedure to deflate the air bags and drain the main tanks?

I don't have any experience with air systems and need help with:
    • What kind of torque is needed when tightening the fittings?
    • What kind of thread sealant to use?
    • How to disconnect the second check valve?  In the photo you can see what look like grey rings at the end of the hose just before the fitting (one on each end).  Are they some kind of quick connect/disconnect fitting? How do they work?  Can they be reused?
    • Anything else that I wouldn't know to ask about.

A couple of side notes:
1.  On page 2 of the drawing (water separator), it says the pressure relief valve is set for 130 lbs.  On page 3 (air connection diagram) is says it's a 125 psi relief valve.  Mine is stamped 125 psi, 116 SCFM and appears to be adjustable.  So why is it releasing at around 108 psi?  Are we barking up the wrong tree looking at the check valves?

2.  If I understand things right, when the aux compressor isn't running, the solenoid attached to the bottom of the water trap is open and any air back feeding from the main air system would escape through it wouldn't it?  What am I missing here?

3.  Page one of the drawing shows a 5 micron filter by Foretravel that isn't present on our setup and page 2 (water trap) shows a desiccant filter by Foretravel that isn't present either.  Should I add these two items?  I think I read in an older thread that Foretravel stopped putting in the desiccant filters.  Is that true?  Should I be asking FOT these questions?

Joe
2008 Nimbus

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #7 –
I don't have your set-up, so I am only giving information on general air issues as I have cranes that use check valves and relief valves. If the relief valve is stamped 125 psi and is popping off at 108 psi. that would be the first thing to correct in my opinion.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #8 –
Joe, if you have the big FT White Book you may have the air schematic for your coach. If not, call FT and ask for a copy.  You may have to pay for it.  If the drawing you have doesn't look like what you have then it is likely not the right drawing.  These systems changed many times.

The pressure relief valve should only see pressure from the aux pump.  If this is a new recent occurance I would be suspicious of the vheck valve.

The fittings that secure the plastic tubing need no pipe dope or tape.  There should be a copper sleeve inside the tube and double taper collar on the outside of the tube.  The screw cap compresses the collar holding the tube in place and sealing it as well.  Metal to metal connections can use tape or a teflon pipe sealer (pipe dope, wonder why they call it that?).  I always have better luck with the teflon pipe sealer.  I don't know it there is a torque spec. If it leaks it wasn't tight enough.  If it breaks, it was too tight.  Good and snug is OK.

The valve at the bottom of the water trap opens whan the pump shuts off.  The air in the compressor and the water trap and the rest up to the check valve exits there and blowas any water out.  This should not be letting any other air out. If it is then it points to the chack valve.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #9 –

Joe,

You have asked many questions, and it will take a while to work through all of them.  As I suspected, your air system is more complicated than the ones found on earlier model coaches.  It will take some time for everyone to figure it out.

I can answer some of your "easy" questions.

You should not have to dump your air bags to relieve pressure on the air system.  There are check valves in the 6-pack manifolds that will hold whatever pressure you have in the air bags, even if you drain all the air tanks.  Just level the coach however you want it, and use the water drain valves to release air from the tanks.  The coach should remain level.  If it does not, that is another problem.

Regarding the gray rings on both ends of the 2nd check valve.  They look like "push to connect" air fittings.  To disconnect the air line, push the gray ring in toward the check valve, and at the same time push the air line in slightly.  Then, still holding pressure on the gray ring, pull the air line out of the fitting.  There are little steel teeth inside the fitting gripping the nylon hose - pushing the gray ring in releases their hold on the hose.
Kinda like a Chinese finger trap.

Next, about the water separator.  You are correct - if main air system pressure is getting past the check valves, and reaching the relief valve, then it should be escaping through the (NO) normally open solenoid valve #1.  That is, unless the water separator is full of trash, and the valve at the bottom of the clear bowl is plugged up.  In the second photo you posted, it looks like there is some white "stuff" in the bottom of the clear bowl.  It is not unusual to have problems with that NO solenoid valve.

If it was my coach, I would remove all the valves on/around the aux compressor, and check them all out.  Once you know they are all clean and operating properly, then you can see if the original problem still exists, and go from there.

I'm still trying to puzzle out all the different pressure relief values.  They do seem to be confusing.  The fact that the relief valve is "adjustable" is always a source of possible trouble.  Anything that can be adjusted, may have been adjusted by persons who didn't know what they were doing.

One good thread sealant (there are others):  Amazon.com: Loctite 56747 PST 50ml High Temperature Thread Sealant for...

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #10 –
When using any pipe sealant, be carful to not get any inside the pipes/ tubing, especially if you use the pipe tape! Bad things will happen sooner or later.
Richard & Betty Bark & Keiko our Golden Doodle
2003 U320T 3820 PBDS
Build # 6215
MC # 16926
2016 Chevrolet Colorado 4X4 diesel

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #11 –
Thanks for all the great info.  I think cleaning/checking all the valves is a good idea.  I think the symptoms point to both the check valves and the pressure relief valve not being quite right.

I'll let you know the end result.

Thanks - Joe
2008 Nimbus

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #12 –
I noticed that after the 2007 year models that the desiccant filter on the 12 volt compressor was no longer used. I asked at FOT if the system was changed so the desiccant filter was no longer needed. I was told that nothing was changed except it was decided that the desiccant filter was not needed. I then asked if it would be ok to remove the filter in my system. I was told that it would be ok to remove the desiccant filter. I never have removed the desiccant filter, but I do not service it as often as I used to.
Larry and Terry
Ex 2004 U270 36'

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #13 –
Hi All,

Got it fixed, mostly.  Decided to buy two new check valves.  I could blow air both directions through both check valves.  The smaller one that screws into the water trap isn't worth trying to fix (around $7.50 + shipping from mfg in FL), and the larger one was rusty inside and I couldn't get it apart anyway.  I couldn't find exact replacement parts (I'm in B.C. right now), but the pressure relief valve doesn't release when the main tanks hit 108psi.  I did buy a new pressure relief valve that is set for 125psi, but the system seems to work with the old one that releases at "108psi", so I decided to leave it in.  Any reasons why that may be a mistake?

As I got a grasp of how the system works, I realized I don't know the pressure that opens the relief valve since the solenoid valve at the bottom of the water trap is normally open.  I also realized that both check valves have probably been leaking for awhile, but not enough to allow the pressure to build enough to cause the relief valve to open.

I say it is mostly fixed because there is a leak in one of the quick release connections on the second check valve.  I reused the old connectors.  I can wiggle it around and get it to seal, but think it will leak while driving so I plan on getting new connectors in a couple of days.

The crud in the water trap was scum/residue on the bowl itself, like a dirty lime scale.

Out of curiosity I waited to see how high the main pressure would get.  It peaked at 133psi.  Is that too high?  After about 7 hours, the gauges on the dash say 123 psi.

After seeing the rust inside the second check valve, if I had a desiccant filter, I would leave it in.

Thanks again for the assistance.

Joe
2008 Nimbus

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #14 –
Joe,

Sounds like you've got a handle on your problem - just needs a little fine tuning.  As you see, this ain't rocket science.

About the "quick release" fitting leaking.  Try pulling the air line back out of the leaking fitting.  If there is a metal tube inside the end of the hose, remove it.  Take a very sharp knife, and cut about 1/2" off the end of the air line.  Try to make the cut as clean and straight as possible.  They make a tool for this, but a sharp knife (or box cutter) will do.  Make sure the end of the hose is round, not crushed by the knife into a oval.  If you removed a metal tube from the end of the hose before you cut it off, replace it.  Smear a little "lube" on the end of the hose (spit works nicely) and insert back into fitting.  Be sure there is no lateral strain on the air line - it should go straight into the fitting.  You should feel a little "click" when the tube seats into the internal o-ring in the fitting.  See if that cures your leak.  If not, then replace the fitting.

http://www.parker.com/literature/Brass%20Products/WC3540.pdf

About the 133 psi air pressure.  On this, you'll get different opinions (what's new?).  I don't think there is any harm in running your air system at that max pressure.  I purposely raised my D2 setting so that's about where my compressor unloads, and my coach is a lot older than yours.  I've never had any lines blow up, or noticed any problems with the high pressure.  If you do decide that you want to lower the cutout pressure, it is not a difficult job, but may involve some gymnastics, depending on the location of your D2 governor.  Read through the thread and the manual linked below, and decide if you want to mess with it.  If you have any questions on the procedure, or the location of your D2, just ask here.

Your wet tank has a safety pressure relief valve on it that should open at about 150 psi.  IMO, as long as you stay below that pressure you aren't likely to damage anything.  Big plus: at the higher cutout pressure, it is a lot easier to fill your tires with the onboard air hose!

Possible D2 Governor Problem

BENDIX D-2 GOVERNOR MANUAL Pdf Download.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"
 

Re: Pressure relief valve on auxilary air compressor is popping off every 2 seconds

Reply #15 –
Thanks Chuck and Jeannie.  I think the problem is too much lateral pressure on the tube/connection.  If you look at the photo posted earlier, the tubing makes close to a 90 degree bend before reaching the quick connect fitting.  A new fitting with new o-rings might do the trick, but I think I'll go with compression fittings.  I assume compression fittings can deal with the lateral pressure better.

The lateral pressure is greater now than before I replaced the check valves because the check valve attached to the water trap is longer than the original and now the 90 degree bend happens over a shorter distance.  I don't know how stiff the tubing was when it was new, but it's pretty stiff now.  Thanks for mentioning alignment/lateral pressure.

Also, I forgot to say thanks to Roger and Susan for pointing out that the Foretravel big White Book may have a drawing for the air system.  It did.  I was so focused on the HWH manual that I forgot about the White Book.

Joe
2008 Nimbus