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I've been following the "portable side blast forge" thread with growing interest as it looks like a good way to go.  However there are some aspects that are a bit foggy for me, for example, the bosh volume.

Mark Aspery has a design for a tuyere and bosh

Building the Side Blast Forge

That design calls for a tank that's going to hold 16 gallons or so, and the instructions specify that it keeps the water from boiling off.

I found this company that makes tuyere's and boshes, however the dimensions listed would put the bosh capacity at around 9 gallons.

I'd be using a 2-1/2" diameter champion hand crank blower for air supply and I'm burning coke as my fuel. 

I found a video here that shows a tuyere design at 15:22 which is designed to be connected via hoses to a remote bosh tank.  I thought I'd mimic it with 6" round schedule 40 tapering to 3-1/2" per Mark Aspery's design with a 2-1/2" air pipe tapering to 1-1/2" inside.  I sounds like I should have a 1" diameter hole in the nozzle plate, but I'd appreciate any guidance from folks who know about these things.

I called around for sheet metal pricing and found that I could buy a metal wash tub or trash can for less than half the cost for enough 1/8" thick sheet metal to fabricate a 9 gallon bosh.  The tubs and cans are lighter gauge, but they wouldn't be as close to the fire, and they comes pre-galvanized. 

As I understand it, the tuyere has to be close to the bottom of the bosh level for the heat to pump the water.  A 16 gallon tub would have about 133+ lbs of water in it, which isn't too bad, but a smaller container would be easier to accommodate in a mobile setup.  Plus that's less water that I have to fill or drain every time I want to move the forge.  We have horrible mosquito borne illnesses out here in Colorado so I wouldn't want to leave stagnant water for them to breed in.

I'd like this to work properly, preferably without scalding hot water right next to where I'd be standing.  Most of the built-in boshes I'm seeing are behind the breastplate of the forge.  That seems like it would give the smith some protection between them and the bosh, but I don't know what a "normal" bosh temperature would be relative to it's volume.

I'd appreciate some help in determining how much bosh volume I'd need to make this work safely.

Thanks in advance

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Rather than try to make it perfect the first time. put a pipe into the fire with NO water jacket. Use 1-1/2 inch pipe with a coupling, and a reducing bushing, so you can change out the bushing to fit a 4 - 6 inch pipe nipple until you get the right nozzle (pipe nipple) combination for YOUR forge and the work YOU do. If you want you can cut a hole in a piece of plate (or brick/mud etc) to stick the pipe nipple through the plate to act as a heat shield. The pipe nipple is a consumable item that lasted 6 months or so at my forge.

Once you have the right combination for YOUR set up, build the bosh to fit. The amount of water and heat absorbed will depend on the fire, any heat shielding you have in place, and the volume of water in the bosh. The bosh should be above the nozzle for maximum effect, always drawing cooler water in and letting the heated water rise to the top. This is considered by some as chasing a gnat for hide and tallow as the temperature difference, I suspect, would be small at the end of the day depending on the volume of water.  If you are concerned about the volume of water needed, add a brick to the water tank to displace or reduce the volume of water.

Remember to leave an area UNDER the pipe nipple or nozzle for the slag and clinker to accumulate.

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Glenn,

I built it with a 15 Gallon capacity and the water gets steaming hot by hour five of forging, but it hasn't boiled.  I built my tuyere to Aspery's dimensions, however I plumbed the tuyere to a remote bosh.

I think it's safe to say that Aspery knows what he's talking about.  It's also worth mentioning that water's cheap and it's fairly easy to re-fill as necessary. 

I think it's highly probable that the tall breastplate on some British side-blast forges kept people from getting too close to the scalding hot water.  If you had a rolling boil going, that plate would keep the water from hitting the smith.

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I'm a bit late to this Rockstar and I'm completely inexperienced so take my input for whatnot is worth!  I just posted on my side blast design and, based on my experiences, I have some insights for you:

 

Dont stress the volume of water too much.  I think you figured that out already though.  It takes a long while to get that water really hot...it's pretty effective as a cooling method.  Also, you may find your blower is not enough for coke.  Come and anthracite both really need constant air.  My air issues have been the biggest hurdle so far.  I'm learning more about supplying air for a forge than I am about forging right now.

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