Air Leak

[garyfrey]

After I shut off my RV ('89 Itasca) I could hear a hissing sound from the back side near the air compressor for the rear suspension.  A quick under coach inspection revealed that the petcock valve at the bottom of the air reservoir is the culprit. If I rotate the knob it alternates from small leak to larger leak then back again, and again, and again. Is this a special type of valve? Also it occurs to me that in order to replace it I'll need to block up the suspension to prevent being squished as a release of the air pressure in the reservoir will result in the air suspension deflating... true? As always, any help appreciated.
Thanks
Gary

 

[Gary RV_Wizard]

What brand of chassis is under the Itasca?  Does it have air brakes & air suspension or just an air bag assist for a leaf spring suspension?

Most likely the petcock is a drain to remove any water that may accumulate in the air reservoir.  It should not leak when closed, so I suspect it needs to be replaced.

 

[garyfrey]

It's a Chevy frame, 454 powered, single axle. The air is for airbag assist suspension, not air brakes. Also I may have used the wrong term "Petcock" it doesn't screw tight, it appears to have an on and off position that are 90 degrees out, but like a petcock on other tanks I've seen it is located on the bottom, so I share your assessment that it's there for water drain. I guess my big question involves what I should expect to happen to the airbags when I remove the valve. 
Gary

 

[BernieD]

I guess my big question involves what I should expect to happen to the airbags when I remove the valve. 

Gary

Most airbags have a bump stop in the bottom for when the bags are deflated. Most diesel pushers on airbags dump all the air from the airbags prior to leveling. Shouldn't be a problem.

 

[Gary RV_Wizard]

Most airbags have a bump stop in the bottom for when the bags are deflated. Most diesel pushers on airbags dump all the air from the airbags prior to leveling. Shouldn't be a problem.

That's why I asked what chassis he has.  On the Chevy P30/P32, the air bags are not designed to deflated when you park and can in fact be damaged if that happens if they happen to get caught in something else (that can happen on the front - don't know about the rear).
I suspect the air bags in this case are aftermarket add-on "helper" springs, since the Chevy chassis I am familiar with had air suspenson only in front, with leaf springs in the rear.  Eithe  a previous owner or the coach builder may have added the air bags a the rear - it was  fairly common upgrade for that chassis.

If the chassis has leaf springs as well as the air bags, there should be no need to worry about releasing the air. If there are no leaf springs,
I'd suggest supporting the body with  jacks, but slowly releasing the air so that the body comes down gently  is probably OK too. Just make sure the bag doesn't get trapped between two "somethings".