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Aux air gauge
Yesterday while driving I noticed something that I hadn’t noticed before. I noticed the aux air gauge at 110 and moving up. I had never noticed the gauge needle moving before. It promptly went to 125 and over time it gradually drifted down to 110 and repeated the cycle again. The cycle varied in time from 8 to 14 min. Apparently there is a leak but I know virtually all these systems leak some. Is this an excessive amount that needs investigating?
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13 Replies
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Mark, That is a significant leak. I am going to stick my neck out and suggest the leak is within the Prevost accessory system because you did not say your aux compressor cycles on and off a lot when you are parked.
A loss of 20 PSI in the length of time you mention might be able to be heard. If it were on my coach which is a similar vintage to yours I would focus on the seat or maybe the belt tensioners. Our vintage of Prevost has 2 accessory system manifolds in the steer compartment and one of the manifolds was provided with a solenoid valve to shut off air flow to it when the key is off. The Prevost pneumatic diagrams for your vintage will identify which circuits are on the solenoid valve equipped manifold. I cannot remember off the top of my head but I will see if I can find which ones are on it.
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Jon, Went we were at the seminar, Jeff replaced the air spitter valve in the front driver side bay with one that I can drain. When it get a bit lighter out this morning I was going to check that for leaks. Probably just coincidental that I noticed it now. I don’t hear it running often at night. I don’t hear any leaks around the seat, will check the belt tension system. I really enjoyed the seminar and all the effort you put into it! Thanks!
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If you are not hearing your aux compressor run very often it is unlikely the problem is associated with house pneumatic circuits so let the coach build up pressure and when the engine driven compressor kicks off, shut down the engine and go around the coach to see if you can hear a leak.
If the planets are lined up just right, if you have good ears, if the leak is in one spot, and if you have been a good boy you might find the leak. Chasing leaks is ranked pretty close to root canal work on the list of things that are fun to do.
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Jon, since I am more aware of this system now, I noticed something else. The dash air gauges after sitting all night. The front and rear gauges still read nearly 120 however the aux reads 0 . Does the aux air gauge not read the pressure when the key is off? Are the slide seals inflated when this gauge reads zero?
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The dash gauge reads 60 when I turn the switch on before starting the engine. So I guess the slide seals are inflated and the gauge doesn’t read when the key is off.
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The reason the dash aux gauge goes to zero is the line feeding the gauge might have a small leak. Turning on the key opens the solenoid valve and lets air back into the circuit.
I should mention that it is not unusual to use accessory pressure when the roads are not straight because with the type of ride height valves on the XLII being instant acting every turn the coach tries to lean to the outside of the turn, and the ride height valves compensate by adding air to the outside of the turn air bags, then as the road straightens it releases that excess air pressure. So on a curvy road or a road with strong sidewinds it is possible the suspension is using the accessory air.
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I would suggest that this is a pretty serious leak and needs to be addressed pretty quickly. I assume you are talking about the 2 chassis tanks and 1 of them is leaking down. I had a similar experience and it was one of air brake lines that has rubbed on something and finally opened a hole. Luckily we were near Prevost in CA and they quickly found the problem, installed a new hose and re-routed it to prevent it from happening again.
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Mark said it was his accessory system cycling and that his primary and secondary were holding pressure. But to your point, a leak in a brake system changes what might be a problem to be concerned about to one of a serious nature that demands immediate attention.
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You may not have anything wrong… 110 – 125 is a pretty slim differential, should be around 20 psi. If you’re on a road that is level and smooth, the suspension shouldn’t have to do any adjusting and aux air should remain constant. If you’re on that level smooth road and your compressor is cycling often, you obviously have an aux leak. You said it still has 60 psi after sitting overnight, that’s not bad.
If you’re on a curvy constant pitching side to side road, the aux gauge will be cycling often.
I think the aux pressure gauge is one of the most important gauges we have, I watch it like a hawk because that gauge will tell you if you have an air problem. Some aux gauges work only with the key on, others like mine are live all the time.
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What Jon and Tom have said is exactly what I was seeing. When the road was straight and level the cycle time was longer. I ran things up and shut off the engine but was unable to hear any leaks in the drivers side front bay or the engine compartment. The belt tensioner seems to be fine and no leaks from the drivers seat could be heard. I will try to soap connectors and see what I find. Thanks for the help!
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Mark, I think you are OK and that the cycling is associated with the suspension working and doing its job.
Before you go through the painful process of chasing leaks note the cycle times of your gauges on the next trip and see if working of the suspension on a road with curves is what you are seeing.
The air pressure gauges are going to cycle and that is expected, but the frequency of the cycling is influenced by road and traffic conditions. It is likely you are seeing normal cycling and if that is the case it will be deviations from normal that will alert to an issue. But it is probable when you do see excessive cycling your aux compressor will be cycling more frequently as well.
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Jon;
I was on the road again today headed West. Jeff Had me air up the coach and drive for a while then stop and shut off the “ Converter “ valve in the front drivers bay to isolate the Prevost side from the Liberty side. The gauge continued to respond exactly as it had before with up and down cycle times unchanged. The Liberty side remained aired up with the drivers seat functioning normally for over a hour and the pocket doors worked after a hour. So apparently the leak, if it is significant, is in the Prevost side.
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Sorry, my old dog Prevost does not have 3 air pressure gauges, only the 2 for the brakes and I “assumed” the OP was referring to one of those gauges swinging.
Thanks for the clarification.
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