Air pressure drop

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Air pressure drop

October 08, 2017, 03:38:02 pm

Newbie question alert!!!!!! At what rate should/does the air pressure drop while going down the freeway on the gauges on the dash. My newbie unknowing mind says mine is going down to fast. In 1 minute and 25 seconds it will go from the high of 110 to 90 and then go back to 110. This seems like a pretty quick drop to me but what do y'all think? this could be close to normal for all I know, I hope I'm wrong...

thanks
Keith

Re: Air pressure drop

Reply #1 – October 08, 2017, 03:48:37 pm

Quote from: hdff – October 08, 2017, 03:38:02 pm

Newbie question alert!!!!!! At what rate should/does the air pressure drop while going down the freeway on the gauges on the dash. My newbie unknowing mind says mine is going down to fast. In 1 minute and 25 seconds it will go from the high of 110 to 90 and then go back to 110. This seems like a pretty quick drop to me but what do y'all think? this could be close to normal for all I know, I hope I'm wrong...

thanks
Keith

It is pretty quick, I would let pressure built up and shut coach off, but leave key on, and leave in travel mode. Then check all height control valves and airbags for leaks. Soap solution works best, but at that rate, should be easy to find.

Re: Air pressure drop

Reply #2 – October 08, 2017, 03:51:11 pm

No question, something is wrong.

When you shut off the engine, how quickly does pressure drop? Both gauges or just one?

When you shut off the engine, when you walk around the coach can you hear a leak?

Re: Air pressure drop

Reply #3 – October 08, 2017, 04:07:36 pm

One simple thing to check: make sure the water drain valves on all air tanks are completely closed.

Re: Air pressure drop

Reply #4 – October 08, 2017, 04:24:26 pm

Quote from: Chuck & Jeannie – October 08, 2017, 04:07:36 pm

One simple thing to check: make sure the water drain valves on all air tanks are completely closed.

I know that there is a tank and drain in front of the drivers side rear wheel but where are the others?

Quote from: wolfe10 – October 08, 2017, 03:51:11 pm

No question, something is wrong.

When you shut off the engine, how quickly does pressure drop? Both gauges or just one?

When you shut off the engine, when you walk around the coach can you hear a leak?

Quote from: jcus – October 08, 2017, 03:48:37 pm

It is pretty quick, I would let pressure built up and shut coach off, but leave key on, and leave in travel mode. Then check all height control valves and airbags for leaks. Soap solution works best, but at that rate, should be easy to find.

I don't know the answers to these 2 questions wolfe and jcus but I will find out.... although my hearing ain't what it use to be I have not heard any significant air loss that I can recall

Re: Air pressure drop

Reply #5 – October 08, 2017, 04:37:11 pm

Quote from: hdff – October 08, 2017, 04:24:26 pm

I know that there is a tank and drain in front of the drivers side rear wheel but where are the others?

Sorry, Keith, I'll have to let some other member answer that for your 2000 model coach. On our old coach, the drains on the 2 front mounted air tanks are valves screwed into the bottoms of the tanks. On your coach, the drains may be remotely mounted somewhere up front.

Re: Air pressure drop

Reply #6 – October 08, 2017, 04:43:12 pm

Quote from: hdff – October 08, 2017, 04:24:26 pm

I know that there is a tank and drain in front of the drivers side rear wheel but where are the others?

The one you know about is the drain for the "wet tank". On our 03, in front of the driver's side steer tire we have 3 drain valves for the auxiliary, rear and front air tanks.

Edit: If your valves are arranged like ours, the valves are:

Outside valve = Aux tank
Center valve = Rear tank
Inside valve = Front tank

Re: Air pressure drop

Reply #7 – October 08, 2017, 06:32:20 pm

I had a similar issue and it was an old pressure regulator under the coach in the front between the two air tanks that failed. The plastic regulator knob was VERY visibly cracked and it basically disintegrated in my hand when I checked it. Motorhomes of Texas had replaced all the air bags on our coach, replaced a stair solenoid, and replaced an air fitting, so I thought the system was good to go. But they left a visibly questionable air pressure regulator in place. Half way through my trip home the pressure on one gauge started fluctuating a lot, and when parked there was a an increasingly noticeable tilt to the coach as my trip home progressed.

Rough road surfaces (Arkansas) made the problem more noticeable. Really really bad roads with lots of bumps, dips, and irregularities can cause the gauges to fluctuate a lot as the airbags try and and compensate, but if the PSI drops as quickly on smooth roads it can be an indication of an issue.

Foretravel's factory leak down specs specify a loss of no more than 6 PSI per hour.

One way to test if the leak down rate is within spec (if you don't hear an obvious leak when the engine is shut off) is to park the coach and keep tabs on the gauges over time.

Before you shut off the engine wait until the front and rear pressure gauges on the dash read the maximum - usually about 100-115 PSI depending on how the air regulator has been set. As you watch the gauges rise while parked and idling, you should hear the pressure relief valve pop off with a "Pssshhhh".

Shut the engine off.

Every couple of hours come back out to the coach, check the gauges, and record the PSI level. This will give you an average leak down.

In a 10 hour period Foretravel's approved leak down rate allows for a loss of 60 PSI. So if you start out at 110 PSI, 10 hours later it is acceptable to be at 50 PSI. Most likely you will see the gauge at 60 PSI for a while.

Chris

Re: Air pressure drop

Reply #8 – October 08, 2017, 06:46:39 pm

One drain for wet tank on. My 2000. In front or driver side rear tire. You have to get on ground and look up at bottom of coach to see it

Re: Air pressure drop

Reply #9 – October 08, 2017, 06:51:01 pm

"In a 10 hour period Foretravel's approved leak down rate allows for a loss of 60 PSI. So if you start out at 110 PSI, 10 hours later it is acceptable to be at 50 PSI. Most likely you will see the gauge at 60 PSI for a while."
If air pressure in your tanks fall below 65 psi in 10 hours, you have another bigger problem, The 65 psi protection valve should stop all air going from tanks to leveling system at 65 psi. This is to maintain enough pressure for your brakes in an emergency.

Re: Air pressure drop

Reply #10 – October 08, 2017, 07:12:58 pm

Jim,

Thank you for pointing out that the protection is at 65 PSI and not 60 PSI. I should have been more detailed and specific.

Chris

Re: Air pressure drop

Reply #11 – October 08, 2017, 09:25:48 pm

I bought the coach at MOT a month ago and they supposedly did a PDI check on all the major components.. I say supposedly cause I found a small air compressor in one of the lower compartments that had the power wire cut... how did they test that system??? Aubrey at MOT told me on the phone that it should have been checked... I put a butt splice spade connection on the wire and the compressor works BUT it bleeds down pretty fast causing the compressor to run often.. I talked to my salesman and he claims that if I bring it back they will check it, we'll see how that works out.....
when I get some time I will go do a leak down test and soap the above mentioned places...

So should the gauges ever go below 65 after sitting for a week or more? On October 2 I ran the coach and pressures up the system to ~110, tonite it was 0 on both gauges,

Re: Air pressure drop

Reply #12 – October 08, 2017, 09:39:10 pm

Quote from: hdff – October 08, 2017, 09:25:48 pm

I bought the coach at MOT a month ago and they supposedly did a PDI check on all the major components.. I say supposedly cause I found a small air compressor in one of the lower compartments that had the power wire cut... how did they test that system??? Aubrey at MOT told me on the phone that it should have been checked... I put a butt splice spade connection on the wire and the compressor works BUT it bleeds down pretty fast causing the compressor to run often.. I talked to my salesman and he claims that if I bring it back they will check it, we'll see how that works out.....
when I get some time I will go do a leak down test and soap the above mentioned places...

So should the gauges ever go below 65 after sitting for a week or more? On October 2 I ran the coach and pressures up the system to ~110, tonite it was 0 on both gauges,

Almost all air systems have some leaks. Not surprising it leaked down to 0 in a week. A lot of fittings, components and connections in the air system. Just a matter of finding the big ones and repairing them before they accumulate and cause big problems. If you do not have a slide the small compressor will try to level the coach ever 1/2 hour if you are in auto level. [if you have slide, it will inflate/deflate slide seals] If it runs a lot in auto level mode, start checking all components, connections, and hwh 6 packs. Try shutting leveling off and see what happens. Many put a switch on the line you reconnected, to shut off compressor just in case you develop an big leak and compressor keeps running and overheats. [New one is close to a coach buck]

Re: Air pressure drop

Reply #13 – October 08, 2017, 09:47:35 pm

Quote from: hdff – October 08, 2017, 09:25:48 pm

So should the gauges ever go below 65 after sitting for a week or more? On October 2 I ran the coach and pressures up the system to ~110, tonite it was 0 on both gauges,

Yes, the air system on every coach will eventually go to zero pressure. Some coaches bleed down fast, some hold pressure for a long time. The protection valves are only designed to hold some brake operating pressure in the tanks long enough to bring the coach to a safe, controlled stop. They are not designed to hold pressure indefinitely.

It is up to you to decide how "tight" you want your air system. At a minimum, it should meet DOT standards (refer to your Commercial Driver's CDL Handbook). Most Foretravel coaches will easily exceed the DOT standard. Some owners don't worry too much about a few air leaks - for others chasing air leaks becomes a obsession. A search on this forum for "air leaks" will give you many ideas on how to proceed.

Re: Air pressure drop

Reply #14 – October 08, 2017, 10:17:49 pm

Quote from: wolfe10 – October 08, 2017, 03:51:11 pm

When you shut off the engine, when you walk around the coach can you hear a leak?

You need to find a young helper. We had a leak, I asked my 21 year old son to help, he identified the location under the coach in about a minute.

Re: Air pressure drop

Reply #15 – October 09, 2017, 11:21:14 am

Back to the OP's post I can comment that my coach does the same thing within the same time frame while going down the road. It has done this for at least the last 20K miles. Static leak down tests indicate to appreciable leaks. I can auto level and both gauges will read about 85 psi for weeks. I' m sure I am missing something so any suggestions that relate to this specific issue will be appreciated.

Re: Air pressure drop

Reply #16 – October 09, 2017, 11:39:16 am

Quote from: SteveB – October 09, 2017, 11:21:14 am

Back to the OP's post I can comment that my coach does the same thing within the same time frame while going down the road. It has done this for at least the last 20K miles. Static leak down tests indicate to appreciable leaks. I can auto level and both gauges will read about 85 psi for weeks. I' m sure I am missing something so any suggestions that relate to this specific issue will be appreciated.

My present coach did same thing. When driving and in travel mode, height control valve controls frame to axle distance, When stopped in level mode, solenoid to hcv is closed, so after those valves leak out, system will stabilize and no more air will be lost. After replacing leaking hcv my compressor load to unload time went from 80 seconds to 200 seconds.
I also held pressure in level mode for a long time.

Re: Air pressure drop

Reply #17 – October 09, 2017, 11:44:15 am

Quote from: jcus – October 09, 2017, 11:39:16 am

My present coach did same thing. When driving and in travel mode, height control valve controls frame to axle distance, When stopped in level mode, solenoid to hcv is closed, so after those valves leak out, system will stabilize and no more air will be lost. After replacing leaking hcv my compressor load to unload time went from 80 seconds to 200 seconds.
I also held pressure in level mode for a long time.

So Jim, did you replace all three hcv's? They're pretty inexpensive and worth a shot.

Thanks for the tip!

Re: Air pressure drop

Reply #18 – October 09, 2017, 11:52:44 am

Quote from: SteveB – October 09, 2017, 11:44:15 am

So Jim, did you replace all three hcv's? They're pretty inexpensive and worth a shot.

Thanks for the tip!

Just replaced drivers side rear, but they are cheap, got a plastic one on ebay for $60. Funny, Foretravel uses the metal ones and Newell likes the plastic ones. I am going to get another one to carry as a spare

Re: Air pressure drop

Reply #19 – October 09, 2017, 02:04:28 pm

Could you tell your hcv's were leaking by spraying them with soapy water?
Do you know the replacement # and is it something that can be done in the driveway?

Re: Air pressure drop

Reply #20 – October 09, 2017, 02:16:52 pm

Not difficult/complex, but you will want to have safety stands in place, as these control coach height!

Re: Air pressure drop

Reply #21 – October 09, 2017, 02:24:20 pm

Yes you can tell, mine was leaking around lever shaft. Mine sits in front of tag tire so a little more difficult to get at. But can be changed in your driveway. Just remember position of lever on shaft.
Freightliner Kenworth Peterbilt Leveling Valve Height | eBay

Re: Air pressure drop

Reply #22 – October 09, 2017, 02:57:06 pm

Safety stands are on the short list to get. Thanks Wolfe

So my front air tanks are basically under the drivers seat in front of the wheel?

Re: Air pressure drop

Reply #23 – October 11, 2017, 07:59:29 pm

So I brought the coach home today and had a chance to poke around on it. First I let the air build up to 110 then killed the motor and left it in travel mode. Checked it all day 110# on both gauges @ 9:30 and at 6:30 tonite it was 67# on both gauges, acceptable by fot standards. Then I soaped all the tanks,bags,leveling switches and fittings I could find.. no major leak and I could ... so why do the gauges go down so fast while going down the road? I have to take it to fot tomorrow and I'll monitor the gauges again...

Re: Air pressure drop

Reply #24 – October 11, 2017, 08:07:58 pm

Pop off pressure valve cycling?

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