Fan Belt Dump Valve Question

[FrontSideBus]

I just replaced the PR2 valve on my MC9.  I tested it before installing it to make sure it would open/close at about 65psi.  I started the bus up and after I shut it down I noticed this loud air leak at the back of the bus.  I went to the back and the fan belt dump valve in the picture was dumping air out of a port on the top of the valve.  What would cause it to suddenly start dumping air, and what setting is it supposed to be at?  Do you think if I hooked the PR2 valve up wrong it would cause this problem?  (I doubt I hooked it up wrong.)

Thanks in advance!

[niles500]

On some of those valves air coming from the exhaust port while in the run position indicates a bad seal - don't know if yours is one - HTH

[bevans6]

There is nothing inside that valve but an o-ring so it is very easy to change.  I think you just have it in the wrong position but I'd have to go look at mine and it is very very cold out...   

Brian

[FrontSideBus]

There is nothing inside that valve but an o-ring so it is very easy to change.  I think you just have it in the wrong position but I'd have to go look at mine and it is very very cold out...   

Brian

This morning before starting the bus I turned the valve back and forth and then left it in the position in the picture (down).  I started the bus up and ran it for a while.  Then I shut her down.  It wasn't leaking as far as I could tell.  I then moved the valve back and forth again and it started to leak in the downward position.  Sounds like a bad o-ring.  I'll replace that and see how it goes.  I also found 2 more air leaks but they are minor.

-Mike

[bevans6]

My handle is 180 degrees out from yours but up and down opens a passage from the supply on the left to the output on the right.  Horizontal closes off the supply and opens the output to exhaust, removing air from the regulator and the cylinder.  So I think you have it right, and it's the sealing o-ring.  I had to change mine.

Brian

[Hi yo silver]

Mine would have blow-by when it was in the fully open position unless it was backed off from the stop, just a little.
Hi Yo Silver!
Dennis

[FrontSideBus]

Mine would have blow-by when it was in the fully open position unless it was backed off from the stop, just a little.
Hi Yo Silver!
Dennis

That's what mine is doing now.  If I have the valve to the left, it dumps air.  Straight down, it dumps are.  In between it doesn't dump air.

[gumpy]

It's fairly easy to tell which is correct (and again, it's cold out and I'm too lazy to go look but I think vertical is on and horizontal is off).  With air pressure up in the bus,
turn the valve. One way will tighten the belt. The other way will allow it to loosen.

If it's leaking, it needs an o-ring or gasket.

The cylinder will probably be leaking some, too.

You should also check the regulator that supplies it. It's probably leaking, too.

[Scott & Heather]

Or do what I did and install a turnbuckle. Remove the air piston entirely. So glad i did this mod!!


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[Larry B]

 On my bus the normal run position is with handle in a horizontal position-facing left. My valve has a little metal stop that prevents handle from moving to dump position on its own while driving. (if you want to dump mine you turn handle up). You should be able to tell by watching tightening cylinder which way air is going as you move handle. Shop air would be safest method to check as the belt  could get quit floppy if you move to dump with engine running. If horizontal is normal belt tighten position you should figure a way to prevent handle moving tto dump on its own. This kind of weather not going to matter but with belt slipage you will likely over heat in hot weather.  good luck
      Larry B

[B_K]

As mentioned above by Larry a way to keep it in the normal position is advised. (especially on a rig run in commercial revenue service w/multiple drivers)
I use a small zip-tie on them and that way I can tell at a quick glance if it's been tampered with!
  BK