Dueldor Posted October 22, 2021 Share Posted October 22, 2021 (edited) Hi all. I am currently building my first forge and I’m having a hard time finding a blower that I like for it. With my setup I am running 1-1/2” pipe into the ribbon burner. I found a couple blowers but one is only 75 cfm and then the next one up jumps to 272 cfm. Nothing in between. Thoughts? Forge is a 20# LP cylinder. [Commercial links removed] Edited October 22, 2021 by Mod34 Commercial links removed per TOS Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted October 22, 2021 Share Posted October 22, 2021 You will be adjusting the output of the blower when in use; so if necessary go high. Back when I built my first blown burner I was able to get a 150 cfm from MSC or Grainger; it's been several decades and I don't remember anymore. Quote Link to comment Share on other sites More sharing options...
Dueldor Posted October 22, 2021 Author Share Posted October 22, 2021 Sounds good. Thank you. Quote Link to comment Share on other sites More sharing options...
timgunn1962 Posted October 23, 2021 Share Posted October 23, 2021 In reality, the CFM rating is meaningless. We are much more interested at the pressure developed at the low-flow end of the operating range. Without the removed links, it is not possible to see whether the pressure is given. Quote Link to comment Share on other sites More sharing options...
timgunn1962 Posted October 23, 2021 Share Posted October 23, 2021 I put together a little spreadsheet a few years ago to try to show the relationship between airflow and fuel consumed. I was having a discussion with a smith who thought he wanted a bigger blower, but actually needed a higher-pressure blower. I don't think I have ever personally seen a forge actually using more than about 20 CFM of air outside of a "proper industrial" setting (Furnaces you could park a small car in and fork-lift trucks with hydraulic "hands" for manipulating the billets). 20 CFM will use a full 47 kg or 100lb Propane cylinder within an 8-hour day. I'm hoping it attaches. On the spreadsheet, the wide range of each fuel consumed for any given airflow is because I have taken the limits as complete stoichiometric combustion to Carbon Dioxide, CO2, and combustion to Carbon Monoxide, CO. We tend to run somewhere within this range (though running even richer on Propane for Heat-Treating is something that some of the bladesmiths do). I would hazard a guess that the smaller blower you are looking at has a 2" outlet and that the bigger one has at least a 3" outlet? If you are reducing the cross-sectional area to a 1 1/2" diameter, you will only get the proportional flow: 1 1/2" is 3/4 of 2", so the CSA of the 1 1/2" pipe is 9/16 that of the (assumed) 2" blower outlet and your maximum possible flow will be 9/16 x 75 CFM= 42 CFM. That would use between 13 and 18 pounds of Propane per hour. If the 272 CFM blower has a 3" outlet, the 1 1/2" pipe will have 1/4 the CSA and 1/4 x 273 = 68 CFM maximum possible flow through 1 1/2" dia. 21-30 lbs of Propane per hour. Obviously I am wildly guessing at the sizes, but if you have the links to the blower details you can probably get the information to do the calculation yourself more accurately. Also bear in mind that if your total burner port area is less than the pipe CSA, that will become the minimum area. If you are using fittings to get the fuel gas to the middle of the airstream, that might be your minimum area. Likewise if you have a baffle plate in the plenum. In reality, the flow-proportional-to-area values are still hugely optimistic because the CFM rating of a blower is based on zero pressure loss on inlet or outlet. Since we pipe the outlet to the burner, there are significant pressure losses as a result of friction in the pipe and these will reduce the flow. The main point I am trying to make is that the CFM rating of a blower, which is often the ONLY information provided by the manufacturer/seller, is not a useful piece of information for us. It's a bit like trying to select a vehicle for snow-plowing when the only information you have access to is the maximum speed. If the spreadsheet does attach successfully and anyone with any understanding of Chemistry wants to sanity-check it, I'd appreciate it: I could be completely wrong and I'd rather know. Calculation of heat produced and fuel used by burning with air.ods Quote Link to comment Share on other sites More sharing options...
Dueldor Posted November 23, 2021 Author Share Posted November 23, 2021 Ok so I found my blower. Now I just need to find a reducer from the blower to my piping. 2-3/4” od of blower to 2” od of piping. Anyone have suggestions on where I might find a suitable reducer? Or possibly another option? Thanks for all the input everyone! Quote Link to comment Share on other sites More sharing options...
JHCC Posted November 23, 2021 Share Posted November 23, 2021 You might find a suitable exhaust pipe reducer at an auto supply store or a vent reducer from an HVAC supply house. However, you could probably do just fine with some thin sheet steel bent to shape and screwed in place. Mock it up with cardboard first, and that will give you a good pattern for cutting the steel. Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted November 23, 2021 Share Posted November 23, 2021 A good plumbing supply store will have reducer rubber bushings. It is what I used from my hand crank blower to a side blast forge. Quote Link to comment Share on other sites More sharing options...
Dueldor Posted November 23, 2021 Author Share Posted November 23, 2021 Awesome! Thanks fellas! Quote Link to comment Share on other sites More sharing options...
natkova Posted December 26, 2021 Share Posted December 26, 2021 I used matress inhaler pump today and I found it useless. It have some regulation of speed how it blows air but it dont have switch to turn on or of and I found my bellows to be dozens time better solution. To be honest even with hradphones for noise I get lost by that sound of working blower. Quote Link to comment Share on other sites More sharing options...
Frosty Posted December 26, 2021 Share Posted December 26, 2021 Every new tool takes some time to get used to and mattress inflators aren't the best forge blower. If you like your bellows then use it until you have to change. I wouldn't stop trying different things something better might be waiting next. Don't worry though, there are other things mattress inflators are good for. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
natkova Posted December 26, 2021 Share Posted December 26, 2021 Well i just wanted to see how it work when i dont pump it how it work by it own, and how heat transfer. I was experimenting. But bellows have more i would say lot's more heat control. Quote Link to comment Share on other sites More sharing options...
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