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Generator Exhaust Hose - Different I.D.'s

Discussion in 'Generators' started by searage, Jan 19, 2013.

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  1. searage

    searage Member

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    I am replacing the exhaust hose on my MDL3. The hose exits the generator and goes into a 90 degree elbow. It then continues to the side of the muffler intake or IN. The intake of the muffler is 2 1/2" OD. The top of the muffler or OUT exits to the thru-hull and both ends are 2 3/8" OD. With some elbow grease I was able to fit a 2 3/8" ID hose on the 2 1/2" OD fittings. My idea was to use the same size for the entire run. It also made sense to me that if I ever had a hose clamp break the hose would still hold because it was a tight fit.

    Anyone out there that has any objections to doing this? I did notice that the new Vernalift mufflers now come with the same ID on the IN/OUT ports.
  2. dsharp

    dsharp Senior Member

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    As long as you got the hose on far enough to double clamp it I don't see why it would create an unsafe condition. I can't picture the hose splitting. I would think after several heat cycles the hose would take a "set" and be fine.
  3. Capt J

    Capt J Senior Member

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    I would not do it. The larger flange will push the wire through the hose because of the extra force put on the smaller hose and it will prematurely wear out. Just but the right size hose.
  4. Capt Bill11

    Capt Bill11 Senior Member

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    While I really don't think it would be an issue, I'd still use the correct size hose if you can.
  5. Marmot

    Marmot Senior Member

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  6. Capt J

    Capt J Senior Member

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    Why add another part/fitting into the equation and another thing that could cause a problem when the correct size hose is easy enough to come by and cheap enough to do it right and keep it simple......

    The reason the discharge side of the muffler is larger, is so that the exhaust is quieter less pressure out the exhaust and also so that the exhaust/water mix loses velocity and doesn't shoot 2' out of the thru-hull in the side of the boat..........
  7. K1W1

    K1W1 Senior Member

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    Hi,

    An 1/8th inch difference will make what is commonly known as a poofteenth of difference to back pressure, velocity etc.

    You are being a scare monger.
  8. Marmot

    Marmot Senior Member

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    I guess I misread the OP and took it as the outlet of one was smaller than the inlet of the other or vice versa and the misfit ends had to be connected.

    If the generator exhaust elbow is the same size as the muffler inlet (2-1/2") then that is the size of hose to use. If the outlet from the muffler to the through hull is 2-3/8" then that is the size of hose to use.

    It is not good practice to try and force a smaller hose on the fittings just to save less money than might be spent having a beer or three after the job is over.
  9. Capt Ralph

    Capt Ralph Senior Member

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    Now think about it this way;
    Your trying to cut corners by smashing a hose and poor fitting barb together. You did damaged the hose and shorten it's life by installing it beyond it's spec.
    Your going to button up this generator project. No matter what you think now, your not going to inspect it regularly. It is going to run a lot. day , night , while your away , while your sleeping.
    That's a poor poker hand.
    Fix it correctly.
  10. Capt J

    Capt J Senior Member

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    It depends on the length of the run. The longer the length, the more difference that 1/8" will make. Over a 3' run, probably a proofteenth of a difference. Over a 20' run, probably a noticeable difference.
  11. Marmot

    Marmot Senior Member

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    There is about a 1mB difference between 2.375 and 2.5 inches over a meter and about 5mB difference between them over a 6 meter run.

    That is based on the exhaust flow of a 12kW generator at 60Hz and full load.

    Not enough difference to try to kludge a smaller tube over a larger fitting just to save a couple of dollars.
  12. Yachtjocky

    Yachtjocky Senior Member

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    Hose

    Read the op again, the inlet into the muffler / water trap is 2.5" and the discharge is 2.375", kind of blows (sorry for the pun) your velocity theory away.

    Now if it was the other way around I could see your thinking however (as usual) you are blowing hot air out of you know what.

    Use the correct size hose for each fitting if for no other reason that if it failed and sunk the boat you may get a smart insurance company surveyor noticing your fix and try and deny the claim.
  13. searage

    searage Member

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    To all forum members that gave there opinion,s it is much appreciated. It was never about saving money. Since clamps are known to fail I personally felt it was better to get a tight fit. I went ahead and used the two different sizes thoughout the system. I also found out that most local marine stores dont usually carry the 2 3/8 but i did locate it together with the 2 1/2 which seems to be quite common. Also, keep in mind that the new style Vernalift muffler are the same size on the inlet/outlet. Another thing i found was that the outlet elbow on the onan generator is larger than 2 1/2 (almost 2 3/4 at the lip). The fun never stops but this project is complete so i can now move on to the next.
  14. Capt J

    Capt J Senior Member

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    I have seen very very few AWAB hose clamps fail in all of my years. They are a very very good hose clamp......ABA is close as well..... but both of these will outlast a standard shields or Breeze hose clamp etc 3 times over and doesn't cut into the hose. I replace all broken hose clamps with AWAB.
  15. Capt J

    Capt J Senior Member

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    I misread which was used on which side, but depending on what you want to achieve as long as it stays within manufacturers specs. The smaller size can be used to increase exhaust velocity and restrict chances of backflowing into the generator if the exhaust comes out on the transom. Ever see a generator where the exhaust water shoots out 12-24" out of the exhaust? Ocean yachts did this on many of their SF. increasing exhaust size not only increases flow, but the water doesn't shoot out as far, and it does quiet it a tad as Marmot mentioned.

    To the OP If I remember correctly, Onan's size on the Elbow is 2 5/8" for some strange reason on those gens.