View Full Version : How to Bleed Air Tanks

09-26-2016, 09:47 PM
:confused: The manual says to drain the air tanks every time that you travel. I looked under my 2004 Royale Prevost and I do see the air cocks for the front tanks. I assume there are similiar tanks in the rear. How the heck do you fit under the coach to turn the bleed valves if you don't have a pit? Is there a cable retrofit to make blleding the tanks easier? Thanks for your help

09-27-2016, 08:26 AM
Yes, there are lanyard attached drain valves. I've never seen them on a motor coach. Given our ground clearance, the lanyard's routing would be critical to avoid accidental discharge from road debris.

The reality is that the air dryer is effective enough to make daily air tank checks an waste of time. Your suspension is supposed to be greased every 5K miles. That interval is a more reasonable interval for draining our tanks. In my short 5 years of coach ownership I have never seen a drop of water drain. If you want a more aggressive interval, I recommend checking the wet tank only. If if doesn't have water, the primary and secondary tanks won't either. Routing a lanyard for the wet tank only would be easy on a H-3 or XL-II where it could be mounted above the rear wheel skirts or even the rear bay.

There is an exception to what I've stated and it depends on how the converter may have tapped into Prevost auxiliary air. The converter's compressor may pass wet air into Prevost aux air system. You should check the small Norgren water separator filter in the front driver's side bay frequently and drain as necessay. The converter may (should) have installed their own water seperator on their cimpressor. Check it frequently and drain the air tank on the converter's air compressor, if it has one.

If your coach has a Jun-Air compressor it really needs an oil separator. As they age they tend to push a lot of oil into the air. Of course, they need rebuilding at that point.

09-28-2016, 12:16 AM
Thanks for the advice. I found two easily accessible air bleed valves, the one that you mentioned in the front drivers side bay and it blew dry air. The HWH compressor in that bay also is dry. The other drain is in the rear passenger engine compartment and it allowed some water to escape. I also just had the purge valve rebuilt and a new water dryer filter. put in I do have a Jun-air in the bay along with the Aquahot. It is switched on or off at the dash. What is this compressor used for besides filling tires?

Joe Camper
09-28-2016, 08:08 AM
If u r disrupting the tank drains looking for water be sure to test them for air tight after u r done. Opening and closing them sometimes pulls dirt and grit in and then they aren't as sealed as they were beforehand.

I second everything Gill suggested.

I saw a solonoid on a programable timer to drain moisture on aux air tank on an entertainer chassis and thought that was very good. The other tanks r not an issue if the dryer is serviced correctly.

If u have a water seporate on the aux air compressor drain it daily untill u get a feel for just how much moisture it's accumulating.

U also have drains on each of the small air tanks attatched to each of your air bags. Do not ever for any reason bleed those no water in there ever.if u do u risk creating a suspension leak resulting in those dreaded leans.

09-28-2016, 10:39 AM
Your Jun-Air compressor is for your auxiliary air needs when parked. Depending on how it is plumbed it can support slide seals, generator air bags, air doors, air seat, stepwell slide, horns, and other air needs. Some converters separate Prevost aux air from converter aux air. When that is the case, the aux compressor must stay on. Otherwise, the aux compressor only needs to be on when the engine is off.