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Delay to fill primary air on start up.
We use to our coach just about every weekend. Therefore it sits for about 5 days at a time. I leave it at ride height with the primary & secondary at 120 psi (the comp cut out). When I return they are both right around 105-110psi. I have no problem with that.
Lately, I have noticed on start up after 5 days of sitting, when I start the coach to build air back up, the secondary will fill along with the aux tank normally. The primary will stay right where it was for about 30 seconds after the air dryer purges then you hear a rush of air in the rear and it jumps to 120 psi just like the other tanks.
I always make sure any moisture is drained (monthly) by draining the tanks in order, I have a new dryer filter (3 months old) and a new governor. Basically, everything is working properly on the air system except for a slight delay to fill the primary tank that is getting longer on start up after the coach sits. No sign of problems out on the road.
Is is there a check valve I’m hearing that is going bad or sticking causing the primary tank to not fill right away with the others? Is it a double check valve? I hear something releasing in the rear like a valve!
Something is sticking.
Thanks!
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5 Replies
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FIGURE 20: LP-3 12078
22. SHUTTLE-TYPE DOUBLE CHECK
VALVE (DC-4)
Maintenance and repair information on the
shuttle-type double check valve is supplied in
the applicable booklet annexed to this section
under reference number SD-03-2202.
The double check valve is located on the
pneumatic accessory panel in the front service
compartment. In the event of a pressure drop in
either the primary or secondary system, this unit
will protect the emergency /parking brake control
valve and the intact portion of the air system
from pressure loss.You can view the pneumatic diagram and access it through this link
https://www.prevostcar.com/contact-us/prevost-service-centers
The above description of the check valve comes from the service manual and may help. The supply to botth the primary and secondary systems comes from a T off the wet tank so all three tanks should fill simultaneously.
https://techpub.prevostcar.com/en/download?id=31&type=manuals_operator&mode=view
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There is a check valve on the inlet to the primary and secondary tanks. The check sticking closed would explan your observations.
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I have both check valves ordered and will advise.
Thanks guys.
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Just to bring closure to my original question, I finally was able to change the DC-4 shuttle valve last weekend. That was the problem that was keeping my primary and secondary tanks from filling equally. I also changed the check valve going into the primary tank when I had it down to change bushings between the rear diff and frame.
Thank you Jon and Joe for the suggestions. This is why I love PC. I was on the road when I ordered the parts and ended up talking to a tech from PASS and he said that shuttle valve was not a likely culprit b/c they rarely have any problems with that piece.
The old part was free to slide back and fourth just like the new one but at some point was getting stuck after a week or so with the coach sitting.
For the future, I would advise anyone to have a coulple compression fittings handy when they disturb the push-in style fitting to swap parts. There are about 9 air lines going into the DC-4 valve that had to be disconnected to get it out and I had one that would not stop leaking when I put them all back in. It didnt matter how much I trimmed back the air line or cleaned it, I ended up having to change it to a compression fitting.
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We have long been suggesting to folks whenever they have an opportunity to replace the push in fittings with compression so your advice is absolutely on target.
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