Testing shop vac performance -or- Do I ever need to replace this CleanStream filter?

[Dan Friedrichs]

I'm building a mini cyclone for my shop vac, and was concerned that it seemed I was getting less "suck" than I expected. So I wanted to come up with a way to measure my shop vac's performance, with and without the cyclone.

I know nothing of fluid dynamics. Is it accurate to say that static pressure is the most reasonable measurement of a shop vac's performance? I don't need to measure CFM's? (I do understand that different shop vacs are designed with different fans that achieve different SP vs CFM, but presuming I am simply looking for a way to evaluate whether or not the addition of a mini-cyclone has significantly decreased my suction, is a measurement of SP sufficient?)

In that case, can I measure static pressure by nailing a piece of clear tubing to a tall board, putting a jar of water at the bottom, connecting the top end of the tube to the shop vac, and turning it on?

Well, I hope that works, because that's what I did. I found that my Rigid blower/vac produced 43" of water using an old CleanStream Pro filter that has been used so much that it won't even rinse clean any more - it's brown.

Figuring that perhaps I could do better with a new filter, I bought a new CleanStream Pro filter, and found that it only produced 44" of water! Only 1" improvement from a dirty year-old filter to a brand new one.

So:
1) Is my test valid? Am I taking the measurement correctly?
2) Has anyone else experienced such a long life of their CleanStream filter? Are these things supposed to be replaced after a certain amount of time?

[hank dekeyser]

Google is your friend for the "suck test" - A cyclone should make no difference on shop vac performance -

I have cleanstream filters on all my shop vacs- after about 5 years of everything from drywall dust to dog hair, I ended up replacing one. What is this "rinsing it clean"?? I knock mine out and blow them off.

[Stephen Cherry]

Yes, you can measure pressure in inches of water column. In the past I have used the U method-- a U of clear tubing with water and measuring the difference in height. with the jar you would measure from the surface of the water to the top of the water in the tube.

Is the vac hose blocked off so that there is no flow? in that case this test wouldn't tell you much because the filter won't have pressue drop without flow. You want to measure the pressure while air is moving through the vac. One way to do this would be to feed a long tube into the vac hose and measure the pressure in the canister while the machine is running.

[Phil Thien]

These days, more and more shop vacs have their "power" specified in air watts. Here is a wikipedia article:

http://en.wikipedia.org/wiki/Airwatt

Both static lift and CFM are important in understanding how much suck your shop vac has.

For my testing I've used a handheld anemometer in conjunction with a tub of water and clear plastic hose.

While it certainly wouldn't impress NIST, it is handy for making relative comparisons that are meaningful to me.

[Dan Friedrichs]

Is the vac hose blocked off so that there is no flow? in that case this test wouldn't tell you much because the filter won't have pressue drop without flow.

Ah, now that's the kind of insight I was looking for. Yes, I blocked off the hose, but it does makes sense that the best test condition would be with lots of air moving through the filter. I will repeat the test in the morning with that corrected...

Hank, I couldn't find anything specific to this problem. I disagree that a cyclone won't make a difference - it will clearly add restriction. By "rinsing it clean", I mean that I take the filter and rinse it with water to knock all the dust off of it. The instructions say to do this. Actually, the instructions specifically state that you are NOT supposed to blow it clean (with an air compressor, etc) - I think it actually says this on the filter, itself.