Reply by Mosquito

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

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9533 posts in 2489 days

#1 posted 10-30-2016 06:25 PM

When I am reading the Flow Chart for static pressure is the CFM going to be the same regardless of the size of pipe / hose being used?? Is the SP the governing rule?

- mrramsey

Similar to what ArtMann mentioned briefly, what a manufacturer states as the maximum CFM, is at 0 SP, meaning no restrictions in the system at all. Think fan with no ducting at all. In exactly the same way, the SP rating is at 100% restriction. Meaning if you cap off the port completely, that’s your peak SP.

The way you would plot the curve, is having SP as the Y axis and CFM on the X axis (or flip them, doesn’t really matter). As you move further to higher CFM, then the lower the static pressure is. Similarly if you increase the static pressure (reduce the diameter of your piping, as an example), you will get reduced CFM as a result.

This assumes that it doesn’t behave like an electronic speed control on a router, where it ramps up the power to keep a certain RPM. Though that would be an interesting concept for a dust collector to impliment too… holding a certain SP or CFM regardless (to a certain extent) of the restriction… hmmmm.

I’ve done a fair bit of testing of PC watercooling components measuring flow rates, static pressure, and plotting out performance curves for pumps, radiators, and waterblocks. Finding real world performance curves are interesting stuff if you’re into that sort of experimenting and discovery lol.

-- Mos - Twin Cities, MN - -

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