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Author Topic: Generator Exhaust Stack, will this work??  (Read 4643 times)
D+C4106
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« on: August 20, 2006, 06:52:08 PM »

Made this exhaust stack today for our Onan 10KW Diesel generator.  Metal tubing is the same size as the exhaust tip on the generator.  Added height of bus plus a few inches.  My concerns are: the additional height, the total length of the exhaust system, exhaust on the roof of the bus, and finally the heat of the pipe near the bus and accessable to people touching it.  Any suggestions or comments will be appreciated.  I am trying to attach a photo hope it works, if not, I will try again. Thanks!  Denis
« Last Edit: August 20, 2006, 06:59:03 PM by D+C4106 » Logged
Ross
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« Reply #1 on: August 20, 2006, 07:27:33 PM »

The stack going up should be larger than the pipe coming off the muffler.  That creates a venturi effect and actually reduced back pressure.  By essentialy adding 13' of pipe to your muffler, you are increasing back pressure by quite a bit.  The large pipe going up to the roof can be thin PVC.  It doesn't get hot because the venturi effect mixes clean cool air with the hot exhaust keeping the pipe cool.    I'll try to take a pic or two of my stack tomorrow.
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JerryH
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« Reply #2 on: August 20, 2006, 07:36:45 PM »

Denis:

Yes, should work fine.  We have an MCI, MC-8 bus done by Custom Coach.  They did (pretty much) the same thing with the onboard 12.5 kW Perkins Diesel genset.

The exhaust is (if I remember correct) 1-3/4" dia. (Huh).  It exhausts on the driver side.  Connecting to that is an extension pipe (in 2-parts), which bends 90-degrees up, then couples to pipe #2, which has a (welded) clip on it.  This clip hangs on the gutter above the window.  The exhaust runs about 2-feet above the gutter.

http://www.busconversions.com/bbs/index.php?action=dlattach;topic=1601.0;id=1360;image

I cannot speak for the venturi effect or any back pressure.  However the pipe does get hot, but is wrapped with heat insulation wrap from bottom to top.  The two pieces separated fit neatly below in the rear cargo bay.

So a short answer -- yes.

Jerry H.
« Last Edit: August 20, 2006, 07:43:02 PM by JerryH » Logged
busnut104
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« Reply #3 on: August 20, 2006, 07:57:19 PM »

I used 1.5" tail pipe and a 90 and going up along side the coach to the top of the roof I used 3" light weight sewer and drain pvc pipe. I was afraid  that some one might touch the metal pipe and get burnt. Works good. I used to sections, makes it easy to store and handel
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HighTechRedneck
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« Reply #4 on: August 21, 2006, 04:30:53 AM »

Just curious, are these removeable when not in use or are they permanently mounted?  If permanent, do you use any kind of rain deflector to keep rain from sending water down the pipe when not in use?  When used with a diesel genset do you have any problem with soot on the roof?
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kyle4501
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« Reply #5 on: August 21, 2006, 05:14:43 AM »

Do be careful with the PVC & 'venturi effect'. I have seen one & it didnot work. The PVC softened & made a mess. But, it can work, I suppose.

You should oversize the additional stack to minimize back pressure. If you leave a radial air gap where the stack & exhaust pipe meet, the chimney effect should bring in excess air & reduce the temp of the gases. (But this depends on a lot of other variables, so you will have to see what works for you.)

If your exhaust system develops a leak, increased back pressure will make it worse. (BTW, any leak in the exhaust should be fixed immediately.)
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JackConrad
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« Reply #6 on: August 21, 2006, 05:29:28 AM »

We made our vertical stack as follows: a 90 degree sweep slips over the generator exhoust at the edge og the bus below the baggage door. A 2' length of 1 3/4" exhaust pipe fits on the 90 and sticks straight up. A length of 3" PVC pipe slips over the 2' sectiuon of exhaust pipe. The 3" PVC pipe is in 2 sections (for easier storage) and has a clip near the top that hooks on the drip rail. The space between the metal exhaust pipe and PVC serves 2 purposes, It allows cool air to be drawn in at the bottom of the stack and prevnts anyone getting burned. The metal exhaust pipe is cented in the PVC pipe using screws as in the photo
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« Reply #7 on: August 21, 2006, 12:03:40 PM »

Jack you need to paint that exhaust stack ! It makes the sharp looking bus, look bad! BK
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« Reply #8 on: August 21, 2006, 01:51:54 PM »

I guess I need to make a new one before we go to Dallas & Cat's Shindig. That was an old piece of PVC I had laying behind my shop. That was the color it was before I started the generator.  Jack
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« Reply #9 on: August 21, 2006, 06:11:00 PM »

I tried the PVC stack at Jack's house. I used 2inch PVC, It worked fine at idle, pipe did not even get hot!!! At full load pipe melted!!!!!! (I have a gas Honda 6010 noisemaker) Go with the 3 inch.
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D+C4106
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« Reply #10 on: August 21, 2006, 06:53:28 PM »

Thanks everyone for your input,  I think I will revise to the PVC,  I was going to ask if that was discolored from heat but you beat me to it.  Jack, do you think it will get  hot enough to ruin a paint job on the pipe?   Does anyone have problems with soot / smoke from the diesel on the roof ?    Thanks everyone,   Denis
« Last Edit: August 21, 2006, 06:58:42 PM by D+C4106 » Logged
WEC4104
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« Reply #11 on: August 21, 2006, 07:03:21 PM »

I too, recommend an increase to the pipe diameter for the vertical section, primarily for back pressure reasons. If the same size pipe is used the engine has to work evan harder to exhaust the gases.

The larger diameter pipe will also be cooler (for several reasons).  I assume you will have an adapter that will provide a sealed connection between the two different diameters.  If so, I don't think you will get much cooling from "clean cool air" mixing in with the exhaust. The pipe will fill up with dirty hot exhaust at a positive pressure, so fresh air is not going to enter and fall down inside.  However, anytime gases go from higher pressure (small diameter pipe) to lower pressure (larger pipe) there is some cooling.  Let the air out of a tire, and the air feels cooler than ambient.  Or, as you use propane, the tank gets cooler.

A larger size pipe also has more surface area with which to disipate heat.

Personally, I like the pipe inside a pipe approach.

Wayne
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« Reply #12 on: August 21, 2006, 09:13:45 PM »

Why would you want a "smoke stack" up the side of any coach? Huh
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akbusguy2000
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« Reply #13 on: August 21, 2006, 09:30:44 PM »

I just finished building one based on the Gen-Turi design, except I used 3" thin-wall fiberglass tubing.  It's stronger and lighter than the PV stuff, not subject to the heat, and takes a paint job well.

Here's a llink to the Gen-Turi:

http://www.magnacoach.com/genturi.html

tg
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Dave Siegel
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« Reply #14 on: August 22, 2006, 03:15:11 AM »

This reply is intended for beatenbo.
Often when you get into tight camping situations and you are parked very close to your neighbors, and as your gen set is running the exhaust fumes will fill their coach and make it very uncomfortable for them. The answer is a temporary exhaust stack that can be broken down and stored away when not in use, that sends the fumes above the roof line.

Your coach looks newer and is probably well insulated , so you haven't had the pleasure so smelling your next door neighbor's exhaust fumes. If you did then you know what I am talking about.

The second reason is, the exhast stack REALLY reduces the noise from your gen set. You may think it's very quite now, but wait until you put one of these babies on. You'll be amazed.

Stated simply, it all comes down to courtesy to your close neighbors while enjoying your coach.

Dave Siegel
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