Size of bellows chambers

[Grafvitnir]

Hi,

I've been reading about double chamber bellows and have find two opposing views in regard to the proportion of the upper and lower chambers. Some say that it is better to make the lower chamber twice the volume (or size) as the upper chamber. (Hrisoulas) I've also read in various threads (iforgeiron) that it is better to make the upper chamber twice the volume as the lower. I think the last one is better because that way you could still have air blowing into the fire after the last pumps; maybe keep coke from dying out. But not having made nor used a double chambered bellows I can't be sure.

What does the more experienced users of bellows think of this?

Thank you and sorry for asking these maybe not important questions.

Rubén

[CurlyGeorge]

Ruben, I use a double lung bellows on a forge cart at a historic site. I was not involved in building it. But the one that I use has about double the capacity on the lower chamber than the top. This seems to work well. The top chamber fills quickly and you can rest your pump arm while air is still feeding into the fire. Make sure that the valves between the two chambers are large enough to accept the volume of air that you are transfering up. They did say that they had a problem with that, when it was first built. Also, the same goes for big enough valves on the bottom, so that the bottom chamber recovers fast enough to keep the top one full. Hope this helps. :)

[Jymm Hoffman]

I am in favor of and recommend the top be larger than the bottom. I have cut down larger bellows, (about 1 foot off the back in order to fit my traveling forge (cart.)) This made for a smaller "foot print", but with more leather on the top they actually work much better than the larger version with the leather being equally split. It was recommended to me in the early 1980's and that is how I have built bellows since. I have not used one the other way, but it makes no sense to me. It would seem as though you would not use the working chamber to its potential or would be forcing air through the reservoir in such a fashion that would give you an uneven blast (which I can still do with the smaller working chamber.)

[rthibeau]

I rebuilt a set of double lung bellows and both chambers are the same size. It works really well and I have no problem keeping a steady stream of air going to the fire. Once you get the thing balanced so the top chamber falls properly, there isn't any difficulty in working it. So now you have 3 ways to make bellows...which one is better?? Maybe try all 3 and then decide. :)

[Grafvitnir]

Hehehe...

That is what I was thinking. Maybe try the three ways and write a report about it

The three chambered round bellows (thanks for the info again, John B.) had, in a way, double the volume of air in the bottom chambers, and it makes sense in a way. But making the upper (or reservoir) chamber double in size makes more sense to me in that you fill it up and then continues to blow while you are doing something else. And then all instructions, BP's, books, always show them being the same size. Maybe it depends on the size of the bellows. Maybe bigger bellows need equal or greater lower chambers and smaller ones work better with greater upper chambers.

Thanks for the warning on the valve size CurlyGeorge. Maybe that's the other variable.

Thank you all for your input.

Rubén

[Don A]

What about the holes & valves between the chambers?

How big should they be, and how many?

I've seen 'em with two intakes holes and one between chambers.

Any standard rules or ratios?

Don

[CurlyGeorge]

Don, on the one that I use, there are three 4" diameter holes and valves in the center, between chambers. They only put two of them on the bottom intake. We have to add another, as the bottom chamber does not recover quickly enough. If you look in the attached photo, we ended up hanging a couple of window weights on the bottom of the bellows to temporarily help this problem. We are going to put in at least one more valve in the bottom as soon as we get a chance. Hope this helps.


http://s758.photobucket.com/albums/xx224/Curly_George/?action=view&current=LLC14.jpg

[Tri Moon Forge]

For the bellows I made, the bottom board has four 1 1/2" holes with leather pieces as flaps, the board above it has three 1 1/2" holes going into the air box, the one above it has two more 1 1/2" hole with a leather flap. The air pipe going to the forge is 3/4" and blows air very well into the tuyer.

[Grafvitnir]

Thank you all for your answers.

Thanks for the pictures Tri Moon Forge

Rubén