Sound- absorption or reflection

[Pete Masterson]

On Feb 22, 2009, at 12:06 AM, Kurt Horvath wrote:

<snip>

Look at any Prevost conversion the generators are mostly in enclosed
compartments, Birds , at least the PT series are completely open
underneath. I would not worry about maximum insulation in the genny
box. When driving you get air flow, when parked the blower is sucking
air in from some where, some is air is flowing through the genny
box , along with the manifold, exhaust and valve cover blankets it's
already retaining/containing a lot of heat internally that can only
be removed through the exhaust and radiator. If after insulating you
see higher temps. Install a lower temp. thermostat.

Dunno about earlier 'birds, but the PowerTech generator is in a sealed box, except when extended, it's open underneath. The top and sides of the box are covered by a soft foam stuff that has an egg crate finish. (Similar to what you might see in a high-end camera shipping case.) I don't recall what, if any insulation is on the bottom of the box, but the obvious choice was to not have the foam as it would absorb oil drips from the engine and become a serious fire hazard.

The radiator and fan are completely external to the sound cabinet -- and located on the street side, front (just below where the driver sits) fan noise is not much of an issue on my coach. Indeed, from inside, the generator is not especially noisy -- from the bedroom, it's difficult to hear, but (back there) I do sense the vibration that travels through the coach frame.

After my near miss at burning up my coach I'd like to ask the forum a
question.

Has anybody ever checked the condition of the Generator exhaust stack
that goes up through the body? And how would we go about checking it?
It has the potential to be a serious issue should it be leaking
exhaust fumes into the coach.

In my coach, the bottom 1/3 of the roof exit genny stack is visible in the storage bay by the AquaHot. I don't see any ready access to inspect the portion inside the coach. Due to the differences in my floor plan to the more common walk-through bath arrangement, the stack runs up past the shower (to the rear) and behind a 'curio cabinet' near the dining table on the front side. It appears that a generous amount of space is allowed for the passage of the stack. Looking at what I see in the storage bay, it may be a double-wall design.

In my coach the Genny Stack is located next to the Fridge. How well
insulated is it? Maybe that's why my Fridge works great when parked
but doesn't when I'm driving. I almost always run the generator when
driving, and yes it's running while parked if not at a place it can
be plugged in to. So is it part of my Fridge cooling problem? Maybe,
any thoughts?

Kurt Horvath
95 PT 42
10AC

I note that the owner's manual in my blue box suggests that the cap on the lower generator exhaust outlet (under the edge of the coach just below the roof-exit pipe) be removed when traveling on the road. I also discovered that it's probably just as well to operate with the lower exhaust port open in all situations where it is practical.

I was going through air filters quite rapidly (the engine breather tube exits about a foot from the air filter intake -- inside the engine box). I subsequently installed a longer breather tube and routed it past the seal where the generator box opens. (The "seal" is basically the same foam sound insulation used elsewhere in the generator box. It makes a fairly soft closure -- probably to allow sufficient air to enter the box to let the engine run (as I didn't observe any other openings in the box -- but that doesn't mean that some other opening isn't present). Once I rerouted the breather tube, the air filter changes were significantly reduced.

Anyway, the first sign that the air filter needs replacement is seeing excess soot in the genny exhaust. Not realizing that air filters were the heart of the problem, I had let the soot condition continue for some time while I did a number of other troubleshooting efforts. (I ruled out the air filter because I'd "just replaced it.") Ultimately, I realized it was the air filter -- replaced it -- and the generator ran a lot better -- but it still seemed to be running short of ideal. I then removed the lower genny exhaust port cap (for the first time since buying the coach more than a year earlier) -- and a TON of soot blasted out -- it was causing some back pressure in the exhaust system making the engine not run quite right.

The soot made a huge mess, but I've subsequently operated the generator with the cap off most of the time -- only switching to the roof exit parked where I'll need to use the genny regularly.

So, Kurt, to eliminate the worry while going over the road, take the exhaust cap off. Be prepared to be impressed by the amount of soot that's collected -- soot that is also a potential fire hazard. Note: stand clear of the exhaust exit when you start the generator -- and choose a location where a LOT of soot will not present a problem. Leave the cap off while operating the generator over the road. Use the cap when boondocking where routing the exhaust out the roof is a wise practice. Hint: put the cap on or take it off while the generator is not operating and the pipes are cool to the touch (so you don't get burned).

As for the impact (if any) on the operation of your 'frige, have you tried looking in from the exterior access panel that most LP gas refrigerators have? (I've noticed them on older 'birds -- I assume the '95 has one but my all-electric coach doesn't.) Perhaps, using a mirror if necessary, you can see a portion of the exhaust stack from that access point. If excess heat in the vent area behind the refrigerator is a problem, perhaps a small fan might assist in improving the air flow.

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42 (For Sale)

<http://www.aeonix.biz/BBforsale.html>

El Sobrante CA

"aeonix1@mac.com"