How do you measure air flow

[jimbob]

I found a 1725 rpm motor that would fit one of my motorless blowers. I'm going to use and air gate to regulate the airflow. I've read here that 160 CFM is about right...How do you measure that?

[CurlyGeorge]

With a CFM tape measure?B)

[MattBower]

Simple, crude method? Measure how long (in seconds) it takes to fill up a 30 gallon trash bag with air from your blower. (Of course you have to make sure to capture all the air that's coming out of your blower during the time you're running the test.) Call that X. Divide 60 by X to get trash bags per minute, Y. Multiply Y by 4 to find CFM (since 30 gallons is basically 4 cubic feet).

Note that back pressure may have a very significant effect on your blower output, so ideally you'd like to find a way to take that into account when you do the measurement.

By the way, what kind and size of forge are you running? 160 CFM is a lot of air.

[jimbob]

the 160 came from a note Grant posted a while back...one of the blowers at blacksmith depot list 164 cfm another list 112 and still another list 400 cfm; centuar forge pb 50 is 500 cfm. 12 violt dayton is 176 cfm
Curly where do you buy a CFM tape measure sounds right handy

[MattBower]

the 160 came from a note Grant posted a while back...one of the blowers at blacksmith depot list 164 cfm another list 112 and still another list 400 cfm; centuar forge pb 50 is 500 cfm. 12 violt dayton is 176 cfm
Curly where do you buy a CFM tape measure sounds right handy

I know; I've always thought Centaur's seemed way too big for any forge outside an industrial setting. That's why I asked what kind and size of forge you're using. For a while I ran a waste oil forge made from a 14 gallon drum on a 200 CFM leaf blower and had to tune the blower waaaay down. That's a good size forge by hobby standards, and it was running white hot, melting 304 stainless and generally just kind of making me nervous with the amount of radiant heat it was putting off.

I'm just saying not to get too hung up on the number. Even if it's way under 160, give the thing a whirl. You may be surprised.

[pkrankow]

The bathroom vent fan I have that is listed as 50 cfm is fine for my brake drum. Keeping the fire clean is very important because there is not enough pressure to push clinker out of the way.

What you need is pressure to deliver volume, you need less volume if you can maintain the pressure. A lot of blowers keep pressure by wasting air, so you need larger volume.

Phil

[ThomasPowers]

How do you measure air flow?: Too Little, Sufficient, Too Much.

And the amount for each of these will change depending on what your forge is like, what your fuel is like and what you are trying to do.

[jimbob]

the blower I put this motor on has six blades 1 1/4 wide and about 1 3/4 long the nozzel is about 2' outside dia. the presure feels close to my hand crank so I'm guessing it should be about right with and air gate

[Rob Browne]

Forget about measuring the volume. If you have the bits just shove it on your forge and see how it goes. Don't get hung up on numbers, its the outcome that you are interested in.

[Larry H]

I think a 3450 rpm motor would be the one to use

[Ratel10mm]

Forget about measuring the volume. If you have the bits just shove it on your forge and see how it goes. Don't get hung up on numbers, its the outcome that you are interested in.

I'm with Rob here. However the HVAC/R industry way to do it, if you're interested, is to use an anemometer to get the air flow velocity. take several readings across the face of the duct (I usually do 9, more for a larger duct). Velocity times duct area = air flow volume. Or get really clever (expensive) & use an air balancing hood as all the air is directed through the hood, taking care of the calculations for you.