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Replace for Belt Tension Air Regulator
Hello, all, and welcome to a new year.
My belt tension air regulator appears to leak air when it is straight up and down position. To get the air to stop expelling I have to turn it to 11 o’clock position. The original Prevost part number for a repair kit indicates it has been replaced with Prevost part number 640938. I will go to NAPA first to see if they have the part. If not, I will order online with Prevost Parts. What does it take to replace this unit?
Regards,
Ron
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24 Replies
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Ron,
What do you mean by “appears to leak”? are you sure it is the regulator? Or is it leaking from the exhaust port of the 3 way valve?
I chased a similar symptoms a few years back, after replacing the regulatory and valve, it was the belt tension piston o-rings. If you have the big brass (maybe painted) cylinders, when the piston o-ring inside leaks, air will exit out the exhaust port of the valve. by changing the valve position you are closing the leak path but not letting the piston do it’s job.
At that time, prevost had the o-rings in stock but not the seals for the piston rods. But those seals don’t have an impact on the leaking. Replace the o-rings and you may be good to go.
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
Ron, The valves Prevost uses are not the best. I have had leaks in them and the pressure regulator on all three buses.
I used screw jack belt tensioners on my current bus and eliminated the leaking valve, regulator, fitting and mini air bags.
But if you want to retain your air tensioner system consider getting a more reliable regulator and a couple of good quality valves. One to admit air to the regulator, the other to deplete pressure to loosen the belts.
Your brass air cylinders may not be supported if they are leakers.
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Ron, if I understand you correctly, I had a similar situation a while back. It appeared to be the valve, but turned out to be a leaking air cylinder. Check out the thread below. It’s lengthy, but this link should take you to my first post in the thread:
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I replaced the leaky air tensioner regulator on our bus 5 yrs ago with a <$50 unit from Tractor Supply.
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Thanks, all, for the responses. When I say it appears there is a leak, I mean to say the unit with the handle. The handle on that device is normally north and south with pointed end being north. When that handle is north and south air is escaping from the top of the device. I can hear it and feel it escaping from the top.When I turn the handle to where is in the picture it stops the air from escaping.
Like I said before, I have never had an issue with this device, and the handle on the device has always been north and south, eg straight up and down with the pointed end being north/up.
This unit has a brass shock like cylinder just like Chad Spears 1994 Liberty coach. There is no leaking coming from that cylinder.
One other thing, I a week ago I loosened the belts in preparation for putting on a new belt. I decided not to change the belt after Inspecting the belt and finding it in good condition. I turned the red handle to where it was located before and made sure the belt was snug. After running the bus for a bit, putting it back into the garage, shutting it down, I could hear air escaping from the engine bay and discovered the air escaping from the top of the device. There, that is the rest of the story. Good day.
R
1984 96" with 8V92TA
(remodeled Liberty Coach)
Greenwood, MO -
I assumed that you were referring to the valve, with the red handle. Mine was also exhausting air, except when turned to that approximate position. The valve was not the problem, and it took me a while to figure that out. I had a few posts in that thread with pictures and drawings. Even if your valve ends up being the problem, that thread may help you troubleshoot. Here’s a link to my first explanation. There’s more about a dozen or so posts down the page.
EDIT: Ron, I just noticed that you posted after me on that thread back in 2017. You couldn’t see my pictures on your iPhone, so you’d better break out the computer.
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I see you updated your last post, Ron, so one more thing…
The leak on my air cylinder was internal, causing air to bypass it and exhaust out the valve. I did not have any leaks that could be detected at the cylinder.
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Thanks, Chad, for your updates. I am not going to anything with that today. It is cold and snowy here and the garage where she is kept is quite cold. Tomorrow it is supposed to warm to 48 degrees so I will look at it tomorrow. Also, I presume the device with the handle is what someone else referred to as the three port vale. That is what I was going to replace.
Thanks again, PC members, for your responses.
R
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I was criticized by one of the members of the Prevost training team for eliminating the air bellows belt tensioners and going to jack screws to tighten the belts.
His concern was as the engine rocks from the application of torque there is no “give” in the jackscrews whereas the air bellows can compress and expand as needed to cope with engine movement. As I studied that concern I realized as designed, the belts are running between two parts that will not move in relation to one another, such as the fan gear box to the fan clutch, or to parts that do move in relation to another such as the engine pulley to the fan gear box input.
The proof was after a few years of use my belts remain as adjusted and show no signs of wear or damage.
My point is the belt tensioning system as designed and installed by Prevost has a lot of areas that require service or some ongoing maintenance and I am glad I replaced the pneumatic tensioning system. My decision was validated by the Prevost mechanic that replace my fuel injector six pack. He saw the changes I made right away, looked it over and said that is how it should be done. I had just changed the original steel parts with stainless steel parts so when I did have to service the belts I would never have to deal with corroded threads on the adjusting rods or nuts.
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I did the same thing Jon did. So far, very trouble free. Before that, lots of air leak chasing. Be sure to put shaft locks on the jack screws to lock them down after you get things to the tightness you want. Ask me how I know. Mike
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Jon,
Would love to see what that set up now looks like.
Stay warm.
R
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After chasing leaks in the original air system, I put in the jack screw as well. This was a few years ago and I have not had a problem since.
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Millions of cars are around with belts that are tight 24/7 with no problems.
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Here are two photos of the original installation. Since those were taken I replaced the steel parts with stainless steel so if I had to service a belt once tension was removed I could easily spin the adjusting nuts with my fingers.
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When I got the bus my regulator was leaking so I replaced it with new of the same regulator, then I found that 3 way valve was leaking bad so I called Prevost and found it was like $250 bucks so I looked for a replacement had no luck. The only thing that valve is for is for a bus driver to change belts with out tools to let air of mini bags. So I got rid of red knob valve put a 1/4 inch ball valve in before regulator right after new check valve I put in and no more leaks my belts are always tight and if I need to let air out of mini bags I turn 1/4 inch ball valve and push schader valve release air to bags, open ball valve all done, simpler the better.
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