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don schad

Leather bellows sizing

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Hi all,

 

I am working to open up the disused historic forge at the historical society in my town.  The smithy has a leather bellows which is generally in good shape, although the performance was lacking.  After I started a fire the other day I found that it was pretty difficult to get a sufficient amount of air into the fire.  It was enough to keep the fire going, but I was never able to get the fire above a light orange.

 

 At least part of the problem is, no doubt, the plumbing from the bellows to the firepot.  This appears to be "historic" 1 1/2" muffler pipe with two 90deg bends before entering the tuyer. post-3041-0-68702900-1368215287_thumb.jp In addition to this I am wondering if the bellows themselves aren't on the small size, although I don't know how these things would be sized for a firepot or a particular forge. The dimensions are 29"W at max width, 18" both extended up and down, 43" long.  The output is a 1 1/2" outlet.

 

post-3041-0-87460800-1368215403_thumb.jp

 

Fortunately the forge is a 19th century one, and there is a rotary blower there so I am going to likely use that one instead.  Hopefully this will work better, and it should at least be in a better position relative to the forge.

 

Any thoughts or recommendations are welcome.

 

Thanks,

don

 

 

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well from the looks of things the bellows was made modern day and while it does not look like a bad job i believe the bottom chamber is not as large as it should be. whoever built the bellows probably  did not know the guideline for bellows of 2/3 bottom 1/3 top. you could probably make them work by changing the leather for a bigger hide which would allow you more depth on the bottom chamber which would give you more volume. you might have to inlarge the valves and the passage from the upper chamber to the pipe also . those are the areas that seem to cause the biggest problem . make sure the bellows is also sealed well as leakage will cause poor performance. Bellows will work and i find them enjoyable to use in a historic situation. .

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You might take a little time to look in the tube and all the connections in the line. It is pretty common for mice, wasp, critters to build nest in any little hole that is open. Last time I tuned on my gas forge after a month away from the shop there was a mouse nest in the blower tube. 

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well from the looks of things the bellows was made modern day and while it does not look like a bad job i believe the bottom chamber is not as large as it should be. whoever built the bellows probably  did not know the guideline for bellows of 2/3 bottom 1/3 top. you could probably make them work by changing the leather for a bigger hide which would allow you more depth on the bottom chamber which would give you more volume. you might have to inlarge the valves and the passage from the upper chamber to the pipe also . those are the areas that seem to cause the biggest problem . make sure the bellows is also sealed well as leakage will cause poor performance. Bellows will work and i find them enjoyable to use in a historic situation. .

 

Interesting, what gives them away as modern day bellows?  They did look to be in relatively good condition when I treated the leather, with a patch on the back side, but beyond that they looked "old".

 

There are a couple of small leaks, but in my estimation they weren't accounting for the low volume at the firepot.  The top and bottom chambers are the same size, although the last person to use them (10+ years ago) had put two bricks on top to restrict the expansion of the top chamber.

 

Thanks for your input!

 

don

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You might take a little time to look in the tube and all the connections in the line. It is pretty common for mice, wasp, critters to build nest in any little hole that is open. Last time I tuned on my gas forge after a month away from the shop there was a mouse nest in the blower tube. 

 

Yes, thanks for this suggestion.  I did checked and clean out the pathways when I got just the tiniest of puffs with my first pulls of the lever.  The equipment was unused for quite a while and it was a bit clogged with coal/ash but I didn't displace any families.  

 

Thanks,

don

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Interesting, what gives them away as modern day bellows?  They did look to be in relatively good condition when I treated the leather, with a patch on the back side, but beyond that they looked "old".

 

 

 

don

well the look of the leather and how far it comes down ...the bricks on the top were probably not there to restrict but to increase pressure.it is common practice to add weight to the top of bellows to increase pressure . volume is determined by the size of the chambers . if you increase pressure but not volume you have to pump faster.I would put the bricks back and try it there . if you have to pump too fast to be comfortable then re leather the bellows and increase the chamber size . good luck!

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They look to be a good size to me (possably a little short in volume if the bottom is fully extended in that picture).
Try re weighting the top, I have also weighted the underside of mine to speed up return rate. Weights do make it harder work but remember that we only have a very limited wattage as human beings so a blower even a small one will outperform even a big set of bellows.

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My humble understanding is that each 90 degree bend decreases air flow by 50%.  I would suggest either changing it to a gentle curve or changing the pipe to two 45 degree bends.

 

Ooops: Looked again, with two 90 degree bends that would result in a 75% reduction in air flow.

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 ...the bricks on the top were probably not there to restrict but to increase pressure.it is common practice to add weight to the top of bellows to increase pressure . volume is determined by the size of the chambers . if you increase pressure but not volume you have to pump faster.I would put the bricks back and try it there . if you have to pump too fast to be comfortable then re leather the bellows and increase the chamber size . good luck!

 

 

They look to be a good size to me (possably a little short in volume if the bottom is fully extended in that picture).
Try re weighting the top, I have also weighted the underside of mine to speed up return rate. Weights do make it harder work but remember that we only have a very limited wattage as human beings so a blower even a small one will outperform even a big set of bellows.

 

I found that I 1 brick seemed most effective for me, but it still required quite a lot of huffing-and-puffing from me.  Where are those apprentices when you need them?

 

 

My humble understanding is that each 90 degree bend decreases air flow by 50%.  I would suggest either changing it to a gentle curve or changing the pipe to two 45 degree bends.

 

Ooops: Looked again, with two 90 degree bends that would result in a 75% reduction in air flow.

 

I definitely agree this is a problem.  It looks like the forge might be undersized with respect to the piping, and the location of the bellows and forge make it hard to have some bends on the way.  The forge was built in the relocated historical building and the blacksmithing equipment acquired during the construction of the forge back in the 1970's.  Unfortunately the forge and bellows were never an active matched set in a working blacksmith shop so it didn't get optimized over time.  

 

Hopefully I can get things improved a bit so that more energy can be spent hammering and less pumping.  

 

Thanks for all the input.

 

don

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I would see if you have a good flow at the bellows and how fast it drops down. At the end of the season I check my bellows by plugging the pipe at the bellows outlet and pumping it up. How fast it drops this tells me if I have leaks in the leather, valves or just overall. Sometimes the valves aren't sealing and the air just goes back and forth.

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