Exhaust

Peter Drouin · October 25, 2015, 07:51:01 PM

I'm going to run the exhaust from my two cats out of the building. And I was told I had to increase the ID of the exhaust pipe from the muffler. Is that true?

Dave Shepard · October 25, 2015, 07:57:11 PM

Unless you are using a vac, I would think so.

dgdrls · October 25, 2015, 07:57:48 PM

do your cats know about this plan?? :D

No really what are you exhausting?

Dan

stihltoomany · October 25, 2015, 08:17:58 PM

Yes. How much depends on how far you have to go. Running the same size pipe will increase back pressure. I assume you are talking Cat diesels. You will also recoup some of that exhaust heat for the cool months.

Peter Drouin · October 25, 2015, 09:52:09 PM

Quote from: stihltoomany on October 25, 2015, 08:17:58 PM
Yes. How much depends on how far you have to go. Running the same size pipe will increase back pressure. I assume you are talking Cat diesels. You will also recoup some of that exhaust heat for the cool months.

About 20' with the mill and 12' with the edger.
Can I just go 2" to 3 " bigger pipe for the whole run?

SawyerBrown · October 26, 2015, 06:31:41 AM

Many manufacturers use most of the engine's backpressure limit with mufflers that get the most sound attenuation ... but that doesn't mean all. If that happens to be the case here, you'll have to be careful not to add much backpressure or you'll suffer some power loss. So the answer isn't as simple as just increasing the pipe diameter, because any pipe (especially one that long) will add some restriction.

That said, unless you want to get into calculating backpressure in your proposed system (difficult since you won't know much of the needed data), over-size as much as you can, keep the runs as straight as possible and avoid sharp 90-deg bends.

Peter Drouin · October 26, 2015, 07:08:20 AM

Thanks for the info SawerBrown, Sound is not the problem it's the exhaust. There will be a 90° on each, or maybe a 45 will work. I was thinking of car hose, Like is used in a garage.

Brucer · October 26, 2015, 10:35:56 PM

Some general guidelines for ductwork elbows.
- large radius is better than small radius.
- 45° elbows are better than 90° elbows.
- smooth curves are better than segmented curves.

And in general, smooth ductwork is better than rough ductwork.

stihltoomany · October 26, 2015, 11:19:05 PM

You will have to have some steel pipe until the exhaust cools down enough not to melt rubber hose. you will be under load, much more heat. If exhaust is 2" I would run 4" pipe for sure on the long run. No science here just seat of the pants engineering.

Kbeitz · October 27, 2015, 07:25:10 AM

Instead of elbows use sweaps...

OntarioAl · October 27, 2015, 08:58:09 AM

A couple of thoughts.
1/ A 3" pipe has better than double the volume of a 2" pipe/
2/Whether it exits horizontal or vertical provision must be made to keep water and other things (bees. wasps, birds) out.
3/ Depending on the length of the exhaust pipe and its thickness you may or may not develop a harmonic noise that can be to say the lest aggravating.
Years ago when I was supervising Koehring shortwood harvesters we had an elaborate heat recovery system (foisted on us from above) connected to our 25KW Cat for winter operations (in our mobile shop). In short the generator only ran at capacity when we plugged the five machines for the weekend (4000 watt heater load for each machine) so heat recovery when the shop was occupied was minimal. The piping did set up a harmonic hum that was cured when We collectively disconnected the system.
Al

Peter Drouin · January 11, 2016, 05:21:02 PM

So what do you all think will it work?

Chuck White · January 11, 2016, 08:43:12 PM

Looks good Pete.

The only thing I might have done differently would have been two 45° elbows instead of one 90°, but I believe it'll work either way!

Peter Drouin · January 11, 2016, 09:41:09 PM

Quote from: Chuck White on January 11, 2016, 08:43:12 PM
Looks good Pete.

The only thing I might have done differently would have been two 45° elbows instead of one 90°, but I believe it'll work either way!

I did think of that. Went with a 3" pipe, the muffler is 2¼".

r.man · January 12, 2016, 07:43:45 AM

Looks good, if you do experience power loss you could either switch to two 45s or remove the original narrow restriction at the top of the muffler. Either should relive some back pressure. If you are really unlucky you might have to do both but my inclination would have been to do exactly what you did first and see if it works. KISS all the way.