CFM Calculations

M

Manitario

New member
Hi, I'm curious what CFM #'s those of you that have done testing have gotten for your Clearvue 1800 systems. I've had a Clearvue 1800 for several years and tested it with several different workshop setups using a Dwyer 166 pitot tube and a digital manometer. I calculate using the raw inchesWC and a Dywer app that takes into consideration all the other variables like air temp/pressure/humidity and duct diameter. My shop is large (longest run ~30ft) with 11ft ceilings; I run 6" metal pipe with 6" drops, minimal flex tube, no 90 bends (all drops are on gradual wyes), meticulously sealed joints (smoke tested) etc. Even with this setup, I still get smaller CFM #'s than I'd expected when I bought my Clearvue. Overall static pressure for the system is 11.1.
The attached file shows the CFM for my various machines and the final duct size (reduced right at the machine) Best run is the first drop from DC (and the only machine with a true 6" opening) which gives me ~1100CFM.
Outside of the CFM #'s, the system does keep the air clean (Dylos particle counter consistently has lower #'s in my shop than in my house).
 

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I do not have data to compare with your values, but your numbers really do point to the profound drop in velocity that occurs due to the port size on various tools. Your mitersaw shows the highest airflow value and, being the closest drop and an unrestricted opening, shows a fairly high cfm value. I am curious about two things -- 1) are your filters fairly clean, and 2) how many blast gates are open during the readings (the s.p. values show pretty low losses).

And, what is the derivation of the 11.1 s.p. value for the whole system?
 
yeah, I suspect that the main cause of the lower CFM is as you said, the restricted openings for each of the machines. Sadly, most of the machines do not make it easy to put a larger port on them, not at least without a welder and an acetylene torch. The previous biggest dust producers, the mitre saw and table saw are virtually dustless right now; the bandsaw and router table are now the biggest problem dust-wise, but this is more a reflection of the design of the machines and the difficulty getting good dust collection on them rather than the Clearvue.
 
I get 1007 cfm on the best run as measured with a dwyer pitot tube and a u- tube manometer. I measured peak velocity at the center of the pipe and multiplied by 0.9 for average velocity to calculate cfm. This is with an early cv1800 without the noise reduction stick. Also, it is measured in 6" sdr-35 with sufficent straight runs on both sides. Results for all of my drops are in the gallery. As i have noted before it is very difficult to get much more than 1000 cfm with the cv1800 in 6" pipe even with clean filters.
Bababrown
 
Hi mate, where are you measuring the static pressures for each machine? The numbers seem very low (low static pressure drop which indicates very low restriction to flow). We're you measuring at the cyclone inlet?

I assume the 11.1 inches of static pressure is measured with all ducts closed? If so that seems in the ballpark, particularly if using filters / not venting directly outside. My clearvue with 16" impeller gets 15.2" at 62 Hz, venting outside. I still only measure about 1000cfm or less to most of my machines running 6" ducting but as you say it works extremely well and for my tablesaw, bandsaw and thicknesser I am dust free. At least I can't see or smell any dust whatsoever.
 
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