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Author Topic: Generator Exhaust Stack, will this work??  (Read 4791 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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« 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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« 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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« 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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« Reply #15 on: August 22, 2006, 04:08:01 AM »

Jack, do you think it will get  hot enough to ruin a paint job on the pipe?
     My stack was made and used witth our old Onan gasoline generator. The pipe did discolor slightly in the area where the 2' piece of metal exhaust pipe ended. The temperature in this area would show about 100-110 degrees. I have not checked the temps with the diesel generator.
 
except I used 3" thin-wall fiberglass tubing
       Where do you get 3" fiberglass pipe? 
                                                                   Jack
« Last Edit: August 22, 2006, 04:11:11 AM by JackConrad » Logged

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« Reply #16 on: August 22, 2006, 09:52:57 AM »

PVC piping has a maximum temp rating of 140 degrees before it becomes soft and starts to break down. Use CPVC piping instead schedule 40,80 or 120 it has a maximum temp rating of 200 degrees before softening and melt down. Go to www.harvel.com and you can read up on pvc/cpvc piping. I had a high efficiency boiler in my house and it used schedule 40 for the intake air and the exhaust air, probably not as hot as a diesel generator but in the winter the cpvc exhaust side would only get warm even after running for awhile. Do not use this piping as an exhaust pipe, use it as the venturi pipe around the exhaust pipe it will withstand a higher temp.
« Last Edit: August 22, 2006, 09:57:28 AM by scanzel » Logged

Steve Canzellarini
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« Reply #17 on: August 22, 2006, 01:28:34 PM »

Thanks for the info. I never got in a situation like that. Usually in a truck stop or some place like when gen running. Makes sense . Put on take off as needed. Wasn't trying to be tacky. I really don't think engine stacks up the back are attractive. Guess that's why over a 100 ice cream flavors. Thanks and have a good day.
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« Reply #18 on: August 22, 2006, 04:11:51 PM »

2" x 3" Alum Gutter Downspout works great for me - bright white / thin / lite weight
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« Reply #19 on: August 22, 2006, 05:24:39 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://http://www.magnacoach.com/genturi.html

tg


tg

Can you clue me in on the thin wall fiberglass pipe? I've never seen it, where is it available? If it's cost effective, I'd think it's a better solution than 3" PVC which will be bulky & heavy.

KC Eagle
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« Reply #20 on: August 22, 2006, 05:34:30 PM »

So, I took this all one step farther. . we, let me clarify, I made Larry take it one step further, ha ha  Wink. I had him run our generator exhaust up through the INSIDE of our bus. Shocked

Our ultimate goal is to have a bus that is peaceful and comfortable, not just for us, but also for our neighbors.  The pipe runs up and through the roof, and we made a sleeve out of double wall type B flue pipe.  This gives us an air gap around the exhaust pipe, and since the flue pipe sleeve extends down into the generator compartment, it can actually draw air up through the sleeve, exhausting up above the roof.  Larry built a "cap" that has an airgap allowing the air to travel out of the sleeve, but atually covers the outlet.  It turns at the top, sort of like a truck exhaust, so that it doesn't rain down into it. 

I will incorporate the exhaust stack into the cabinetry, further quietening it, but I agree whole heartedly with the fact that getting that exhaust up, overhead, not only makes it quieter but also allows the air currents to waft those stinky  Tongue diesel fumes away.  Larry was thrilled with me, as you can imagine, but he really rose to the challenge and built a great setup. What a guy! Grin  Christy Hicks
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« Reply #21 on: August 22, 2006, 05:35:25 PM »

I would forget the PVC and wrap the extension with a good insulation of some sort.

I'm going to use the wet-blanket stuff from EHP on my new Honda EV6010 muffler, exhaust and extension. No body will ever get burned if that stuff is on the pipe. They also have a tube type that just slips over the pipe but I've never used it.

I used it on my current Onan and it cut down the heat more than 50% plus helped reduce the noise.
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« Reply #22 on: August 22, 2006, 08:07:02 PM »

I agree with using the aluminum rain gutter, its large enough so the heated exhaust pulls fresh air along with it as it goes up the pipe keeping it cool (warm to the touch), light enough to mount with one small angle clip after setting it on the generator pipe, will not burn or melt, and its strong enough to hold up to reasonably heavy winds.

Two sections fit together in seconds, the entire mounting of mine takes less that 2-3 minutes, half of wich is getting it out of the bay.

Jim Callaghan 4106
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« Reply #23 on: August 22, 2006, 09:11:11 PM »

KC Eagle:  I live in Alaska where they use quite a lot of fiberglass piping of all sorts for sewer lines in permafrost zones, as well as in the oilfield.   I found a supplier here in Anchorage that had a few scraps lying around, which they gave me.  I had to buy a two-piece threaded joint, since I wanted to make up two pieces about 5 ft each.  I'm afraid if one had to buy this stuff it would not be very cheap - the joint was over $50.00 alone.

Pros:  the stuff is great to work with and the joints cemented on with Fliberglass resin, which I had lying around the garage anyway.  Its light weight, very strong, and took a paint job well.

Cons:  Only one.  The thin walls give it a peculiar accoustic effect - it seems to resonate like a straight pipe and that makes it a littlel louder than a heavier one would be.  I'm going to experiment with a wrap of some kind to see if it will help.

By the way, I did some trial and error testing when building the setup to see how long the steel exhaust pipe should extend into the venturi pipe.  I found that there is a sweet spot with the metal pipe to terminate precisely at the same point the venturi begins.  The further it extends into the venturi the louder it gets.  To make sure it's working as it should you can release a small wad of tissue paper at the bottom of the venturi and see how quickly it spits out the top.

ymmv


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« Reply #24 on: August 23, 2006, 06:18:35 AM »

Christyhicks - can you send a picture of how you sealed the top? Did you use a flange at the top, and if so, how did you make it?

Thanks

Jim
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« Reply #25 on: August 23, 2006, 11:28:30 AM »

Yeah Christy, we need pictures!!!  Grin
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« Reply #26 on: August 23, 2006, 05:19:58 PM »

I'll try to get some closeup pictures for you guys, no later than this weekend.  It's pretty cool if I do say so myself, but then, I always said that Larry was the most talented guy I know!   Grin  Christy
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« Reply #27 on: August 24, 2006, 05:02:45 PM »

My friends and I got some 4" diameter double wall fiberglass pipe free at a Flying J truck stop last year.  I think it wasn't long enough to be of any use to them.

Anyhow, I have an older Onan 7.5KW diesel generator, and 95% of the noise comes from the generator itself, not the exhaust.  We put a really expensive muffler on the exhaust and couldn't tell the difference in noise with the muffler on or off.

The generator is so loud that I really want to get one of the Powertech quiet ones if I ever come across some extra cash.

Brian Elfert
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