I,m in possession of a blower  with a 6" dia (blades 1.5)  6 blade fan, outlet is 2.5".  I am considering using this on a back blast type forge.   Could someone give me a clue as to what maybe a suitable speed  to run it at  in this application. Thank You. 

Fast enugh but not to fast....

fuel type, tuyere size and cfm output of the blower are all variables. 

Please explain a back blast type forge.

Fuel does not make the fire hot, air makes the fire hot. You can control the air by controlling the fan if that is an option with the fan you are using, or you can vent any unwanted air. I prefer to vent unwanted air and channel it to blow on the blacksmith, keeping him cool.

Your question is exactly the same as if I were to ask you how fast to drive my car to the store.

If you're wondering about a maximum safe speed to turn the impeller I'd keep it pretty slow and work up gradually to make sure it was well enough balanced and sound.

Frosty The Lucky.

7 hours ago, Glenn said:

Please explain a back blast type forge.

 

          I don't think it requires  any explanation  and  I'm sure most readers would have realised that the term SIDE BLAST should have been used.

Just trying to get one set of terms, and everyone on the same page. Thanks.

is this a new blower or an old blower?   The old blowers usually ran at reduced speeds compared to modern ones.

2 hours ago, ThomasPowers said:

is this a new blower or an old blower?   The old blowers usually ran at reduced speeds compared to modern ones.

            Could be described as almost new. It would not have been used as a forge blower although its design and appearance greatly resemble one. It is of heavier construction

than the usual blower designed for forge work. Not sure what it was used for previously if it has been used at all, paint is still unmarked around the outlet pipe.

               The unit is marked  DAWN  2 1/2 B          

   Did intend to drive it direct with a 1420 RPM electric, If this is to fast will use pulleys to obtain the correct RPM.

             Have thought of using a temporary set up utilising a B&S engine or a  tractor belt pulley to check the air flow at various speeds.   

Appears to be an Australian manufactured blower.  You can probably source better information over there than I can here. For a similar unit, online, I found the following; http://www.dawntools.com.au/downloads/Dawn_Cast_ Iron_ Pressure_ Blowers_ Imperial.pdf.  If you can get a fan curve for your particular model it will certainly help in selecting the appropriate RPM and motor horsepower.  Of course a lot depends on the tuyer design, ducting to that tuyer, fuel type, scale of work you plan on producing... (as others have stated). 

Without that information we would only be guessing.  My guess would be to go for around 100-200 CFM at 1-3 inches of water gage static pressure (i.e. for the 2F blower in the link that would be around 1/2 HP and around 1440 RPM).

                    Thanks Latticino.                   

                      Typed  Dawn 21/2 B Blower  into Google  and found the blower in question. Is a commercial model original manufactured for dust extraction etc.

                     2850 RPM was the speed mentioned, but I believe in a forge application this speed would have to be greatly reduced.  Have decided to wait until I have built the

                    forge and sort it out by trial and error.