Power Level Leakdown

[dick kennedy]

My coach ('75 Palm Beach) has the original power level system. It works fine
except that the gate valve in the dash has a slow leak. It holds air well
enough that the leakdown is overnight.

The valves are a pin in hole sealed with an O ring. The leak is seepage
around the O ring. As near as I could tell the O rings are standard 9/32 OD
and I've replaced them with new. I believe the hole is a loose fit on a 9/32
drill. I've had the valve apart a half dozen times now and it's much
improved but still leaks.

Earlier I had read on this group that the valve bodies are porous so last
week I heated the cast bodies then dunked them in polyurethane varnish
hoping to seal any possible leaks in the castings. This didn't help
anything. On the last round I used polishing compound on the inside of the
holes. This improved things somewhat but I still have a slow leak on just
one of the pins.

The basic problem is that the O ring doesn't seal well in the hole. The fit
seems to be a little too loose and it probably doesn't help that it has to
slide in pot metal.

I'm sure someone has solved this one before so what are my options. Is
there an improved version of the valve available? Are there better O rings
that solve the problem? ATF has an additive that swells gaskets. Would it
help O rings? How about a stainless insert for the valve body?

Anyway I'd like to know what others have done to solve this.

Dick Kennedy
'75 PalmBeach

 

[balcom robin s]

Dick

A few months ago, I tried rebuilding a spare Power Level valve for my
parents GMC. I used o-rings also, and like you, felt the fit of the o-ring
in the hole was too loose. (I'm talking about the o-ring that goes in the
groove in the middle of the plunger.) I looked closer at the o-ring that
came out, and found out that it doesn't have a round cross-section - the
best I could describe it is like a 4-leaf clover, with 4 round "lobes". It's
more like what you would find on a piston inside a hydraulic or air
cylinder. Which makes sense because that's exactly what that "o-ring" is
doing - sealing a cylinder. The air pressure forces the "lobes" tighter to
the "cylinder" (or in this case, the hole in the valve), sealing the
"cylinder". The same sealing can't happen with a regular round-section
o-ring - the air just leaks past.

I have an industrial supply catalog which has "Double-Seal Buna-N O-rings."
The size needed for the valve is 007. I was going to look to see if I could
find the same thing made fron Viton.

That's as far as I went with that project (other fires to put out...) but
I'll be getting back to it sometime.

(By the way - McMaster-Carr Supply Company, P.O. Box 440, New Brunswick, NJ
08903-0440, Sales (908) 329-3200, Fax (908) 329-3772, Part numberAS568A-007,
$7.79/pkg. of 100.)

Robin
"73 Sequoia
Corning, NY

 

[bartz paul]

Dick:

If you're looking for new/replacement air control valves, perhaps JR Slaten
in Louisville KY (jrslaten ) can help you.

Paul Bartz

- -----Original Message-----
From: Dick Kennedy [mailto:rakennedy]
Sent: Monday, November 23, 1998 6:50 AM
To: gmcmotorhome
Subject: GMC: Power Level Leakdown

My coach ('75 Palm Beach) has the original power level system. It works fine
except that the gate valve in the dash has a slow leak. It holds air well
enough that the leakdown is overnight.

The valves are a pin in hole sealed with an O ring. The leak is seepage
around the O ring. As near as I could tell the O rings are standard 9/32 OD
and I've replaced them with new. I believe the hole is a loose fit on a 9/32
drill. I've had the valve apart a half dozen times now and it's much
improved but still leaks.

Earlier I had read on this group that the valve bodies are porous so last
week I heated the cast bodies then dunked them in polyurethane varnish
hoping to seal any possible leaks in the castings. This didn't help
anything. On the last round I used polishing compound on the inside of the
holes. This improved things somewhat but I still have a slow leak on just
one of the pins.

The basic problem is that the O ring doesn't seal well in the hole. The fit
seems to be a little too loose and it probably doesn't help that it has to
slide in pot metal.

I'm sure someone has solved this one before so what are my options. Is
there an improved version of the valve available? Are there better O rings
that solve the problem? ATF has an additive that swells gaskets. Would it
help O rings? How about a stainless insert for the valve body?

Anyway I'd like to know what others have done to solve this.

Dick Kennedy
'75 PalmBeach