Generators - extending & silencing exhausts

Discussion in 'Machinery' started by edessex, Apr 11, 2016.

  1. This is a two-scenario question really, we'll start with the easier one...


    Extending an exhaust?

    I want to extend the exhaust on a petrol generator, so the generator can be used inside a van or box trailer, but the exhaust fumes need to be routed outside.

    The generator will not be permanently fixed, so a flexible pipe would be the best option. It needs to be able to withstand heat, and transfer as little heat as possible (yes, I know, it's an exhaust so it will get hot, but the cooler it can be kept the better).

    What are the best options?


    Silencing an exhaust?

    I could do with one of the petrol generators running quieter, I was thinking of grafting a moped exhaust or similar on, would it make any difference?
     
  2. Dave W

    Dave W Member

    Location:
    chesterfield
    My generators are in a container so I got a length of proper flexi exhaust pipe and just extended the tail pipe of the exhaust.
    I'm not sure how much difference it will make to heat output if you insulated the pipe somehow. Mine are diesel so probably give off more heat from the engine itself than a petrol would.

    I can't see heat being too much of an issue from a petrol. You can buy heat wrap bandage that will insulate the pipe if it is
     
  3. Netherfield

    Netherfield Member

    Location:
    West Yorkshire
    Putting a wrong silencer on could create the wrong back pressure and do damage to the engine.
     
    Dave W likes this.
  4. Dave W

    Dave W Member

    Location:
    chesterfield
    What size genny are we talking and how long are they running?
     
  5. Netherfield

    Netherfield Member

    Location:
    West Yorkshire
    Local exhaust specialist would be able to help with insulation jacket, we had an ERF truck with night heater, the exhaust was wrapped in something to stop the heat getting to the fibreglass cab.
     
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  6. Mursal

    Mursal Member

    Hotel ERF ...............
     
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  7. Look up "exhaust skin fitting" and "exhaust hull fitting" on ebay for some ideas.

    You'd be ok adding a second silencer as long as it isn't too restrictive.

    if you can point it upwards and raise it above 6 feet it'll be a lot quieter too.

    another option if you're on grass is bury a length of flexi under the sod, does a lot to quieten it.

    you'll find that an aircooled engine will make as much noise from the unit as it does from the exhaust.
     
  8. Lazy Sod

    Lazy Sod Member

    Location:
    Warminster
    The trouble is that a lot of small generator silencers don't actually have a pipe sticking out of them, just an exit hole in the silencer body.
    There is nothing to attach an extension pipe to.
     
  9. Cheers guys. All the generators have a small pipe on the exhaust, only an inch long.

    One is 1000w (extended pipe), one is 2400w (silencer) and one is 6500w (extended pipe).

    I never gave the backpressure thing a thought... Very good point.
     
  10. Dave W

    Dave W Member

    Location:
    chesterfield
    What's 1000w in kva? 0.1kva??
     
  11. ...probably about 1.25 kVA (@ 0.8 PF, fairly common estimation)

    In truth you need to look at the power factor of the load:

    kVA (apparent power) x PF = kW (real power)
     

    Attached Files:

  12. Dave W

    Dave W Member

    Location:
    chesterfield
    1.25kva would have done!
     
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  13. Some good reading for you in this Honda Technical Manual (especially the bits about extending the exhaust)...

    http://www.trictools.com/wp-content/uploads/2015/07/HONDA-GX-390-TECH-MANUAL.pdf

    They even quote exhaust back pressures (should you feel the need to boil the ocean!!)
     
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  14. Mursal

    Mursal Member

    Thanks I'll have a look later, love a pit of the operator J, imaginary power.
    You must be an anorak like me @Pheasant Surprise , but I'm still in the closet though, what about you?

    I wouldn't stress over back pressure as long as you keep the diameter bigger, unless the engine has a turbo, which is unlikely.
     
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  15. Dave W

    Dave W Member

    Location:
    chesterfield
    This is how I did mine. Slightly different scales so maybe not much use
    image.jpeg image.jpeg
     
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  16. That's definitely the sort of thing I want to do, where did you get the flexi pipe @Dave W?
     
  17. eulb

    eulb Member

    Location:
    Lancs
    I've seen flexi pipe on eBay.
     
  18. Dave W

    Dave W Member

    Location:
    chesterfield
    Local motor factors. Wasn't cheap but is the proper flexi twin wall sort of stuff.
    Think it was about £40 a length. Available in different sizes
     
  19. Dave W

    Dave W Member

    Location:
    chesterfield
  20. Mursal

    Mursal Member

    E-Bay has almost everything .............
    Free postage would be next level, like the Chinese stuff ....
     

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