Reply by mrramsey

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Posted on Calculating CFM and Static Pressure.... Confused

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33 posts in 470 days

#1 posted 10-30-2016 03:40 PM

A lot of helpful comments and advice above. Dust collection has been made into an (often) hugely complicated issue, partially by misinformation from manufacturers and partially by a lot of inaccurate stuff online.
Figuring out what DC you need and/or what sort of set-up can be made a lot simpler;
1)Find a good static pressure caluculator eg. as BobAnderton mentioned, the Bill Pentz one is the simplest and easiest to use of all that I ve seen (the one in the Grizzly manual is horribly complicated to figure out).
2)Figure out the max static pressure for your system, ie. the longest run with the smallest diameter pipe.
3)Plug this number into your fan curve to determine what CFM you re going to get from your DC.

This will give you a pretty good approximation of what you re going to get from your setup.

As for your specific DC; it has a massive impeller, which is great for CFM; but is a small motor which means it won t tolerate much static pressure in your system without huge CFM drop-off.

- Manitario

Yes I agree that it can get overly complicated. I had a similar exercise when I built my saltwater reef aquarium. I had a lot of plumbing on drain lines ad return lines, calculating the flow rates based on pipe diameters etc then matching up to the actual pump curve for head loss.

I have figured out my SP’s based on my longest run and worst run. They were very similar. To achieve 800 cfm, if I run 100% 6” rigid pipe and a short piece of 6” flex to the machine I calculated 4.87”on one leg and 4.46” on the other. That included the additional 2” loss for a seasoned filter. Using the fan curve from grizzly as an example do I just look at the curve and plot the calculated SP for the approximate CFM? How do you apply this logic to say the Laguna CFlex 1.5 or 2HP collector where there is not a fan curve listed (that I could find anyway)? They just give a nominal cfm and a real cfm.

-- Mike ~~~ Experience is what you get right after you needed it. ~~~

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