Dust Collection

[Steve Kelsey]

Hi All,

Just setting up shop and I have a quick question on converting static pressure from 6" to 4" and was unable to find a thread that already addressed this. My new Epliog Mini 24 says I should have 400cfm at 6" static pressure. All the dust collection systems I've seen rate them at 4". Does anyone know what the 'conversion' would be? What is the equivalent 4"?

thanks in advance for your help. And thanks to all the posters and contributors on this site. I've been reading many of the threads and have learned quite a bit. I can't wait for the laser to arrive so I can put all your tips/tricks and suggestions to work.

Steve

[Ross Moshinsky]

I wouldn't be concerned. Get something that moves the right amount of air and just use rubber couplers/reducers from Home Depot or Lowes to make it work. The whole point of the system is to take the vapors out of the machine and get them outside. As long as the fan is powerful enough to do this, you are fine. Some people use bathroom vents to accomplish the task. Some people use big industrial fans. In the end, as long as it gets the vapors out, it's doing its job.

I also find on very thin plastics, I will unhook my fan and move it a few inches from my machine. On all the way, the vacuum is enough to lift the material up while engraving. I should make a vacuum table, but my way is free and easy. Just a little stinky.

[Gary Hair]

Ross,
Go to Woodcraft and get a blast gate. You can restrict the flow using the slide. The impellers used in dust collectors are more efficient without any air flowing over them so you'll see the motor actually speed up as you restrict the flow. The motors are fan cooled so you don't worry about hurting the motor.

Gary

[Gary Hair]

Steve,
Go to Harbor Freight and buy the green dust collector that they put on sale for about $90, it's perfect for your laser and isn't too terribly noisy. I have two of them, one for the laser and one for the sandblasting cabinet.

Gary

[Ross Moshinsky]

Ross,
Go to Woodcraft and get a blast gate. You can restrict the flow using the slide. The impellers used in dust collectors are more efficient without any air flowing over them so you'll see the motor actually speed up as you restrict the flow. The motors are fan cooled so you don't worry about hurting the motor.

Gary

Thanks Gary. I was thinking about a ball valve, but they are so hard to get half open and are pretty expensive when you get to 3-4"(I forget what my PVC is).

[Steve Kelsey]

Thanks for the info. I will check the Harbor Freight one.

[Richard Rumancik]

Steve, I see no one has actually answered the question. The short answer is that there is no conversion. And the flow at 6 inches water will be "something less than it is at 4 inches". The reason you cannot convert is because the manufacturer is supplying only one data point on a performance curve, which is not a straight line. See the attached jpg for a generic blower curve.

The shape of a blower curve generally follows this one, but some blowers can have some odd dips and humps in them.

IF the manufacturer provides the "endpoints" in the specs then you might be able to make an estimate.

For example, if they said:

1150 cfm @ 4" water pressure
1600 cfm maximum flow (which usually means 1600 cfm @ 0")
9.5" maximum pressure (which usually means 0 cfm at 9.5")

then you have three points to work from, and you could try to generate the curve by connecting the three points with a gentle curve. Then you could estimate the flow at 6" water. This is not a very exact method but might get you into the ball park.

If you had flow at say 8" and 4" you could guesstimate flow at 6" fairly well (even if you had to assume a straight line curve between them) but you probably don't have those two data points.

If you ask, the manufacture might be able to send you the performance curve. (Ask them if you can get the pressure-flow curve or the PQ curve). Then you don't have to guess.

[Steve Kelsey]

Thanks, Richard. That was very helpful.