Thread: Small duct Measurement

Read the sticky posts directly above yours for more information but the short answer is no, a total waste of time. The bigger question is what are you wanting to measure the airflow for? The information in the stickies should answer most questions about ducting and DE in general.

As an aside from your question 99.9% of information concerning dust extraction on YouTube is simply wrong and should not be relied on. Do some reading here and gain some knowledge and you can then begin to weed out the misleading information from the occasional snippet of useful stuff.

Try this DRAFT: FAQ - Dust Extraction (Practical Aspects)

Originally Posted by Chris Parks

As an aside from your question 99.9% of information concerning dust extraction on YouTube is simply wrong and should not be relied on. Do some reading here and gain some knowledge and you can then begin to weed out the misleading information from the occasional snippet of useful stuff.

fixed

Thanks for the responses...but I think I phrased it not clearly.

What type of setup is needed to measure the cfm of shop vacs? No doubt that you need to use a much larger test duct. How big a test duct and how long? It would seem that if too large the velocity would drop to low.

Originally Posted by Maple71

Thanks for the responses...but I think I phrased it not clearly.

What type of setup is needed to measure the cfm of shop vacs? No doubt that you need to use a much larger test duct. How big a test duct and how long? It would seem that if too large the velocity would drop to low.

Its not that difficult to work it out for yourself.

The flow rate for a typical vac is ~0.06 m^3/s
A 30mm diam hose has a cross sectional area of 0.0007 sqft
This means the air speed is notionally 0.06/.0007 = 85 m/s
Now unless you have an air flow device that uses something like a "pitot tube" there is no way you can measure this air speed.
At this nominal flow rate the air speed is also not uniform across this duct so it has to be slowed right down/\.

This is done by increasing the cross section of the pipe so the ai speed comes into the range of the air flow meter you are going to use.
If you can't work it out then ask and I'll step through it for you.
For that I will need to know the range of air speeds your air flow meter can cope with.
It will also help to know the type of meter you have.

The rest is in this post. DRAFT: FAQ - Dust Extraction (Practical Aspects)

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