CFM & Static Pressure

gotrocks · Jun 12, 2005

This is not tractor related except that I do own a tractor.
Thanks to all you fellow TBNers for past help and suggestions.

Now I am planning to install a dust collection system in my shop.
One blower unit specs state 1900 CFM free air flow and 10.6 " static pressure
another unit 1280 CFM 12.3"

My guess is that the CFM is more important that static pressure.

The sawdust will be drawn up to the ceiling (approx 8') then along the ducts to the blower unit.

I will appreciate any help making me understand the relationship between CFM and static pressure.

Freds · Jun 12, 2005

I only used to install and fabricate the stuff (if it was welded) and the engineers usually figured everything out (although my father used to do that also back in the day they didn't have a 500 page spec book with every job), but the supply house where you are getting your dust collector from should be able to size it out for you. Everything depends on how many pickup stations you will have, how many will be in use at one time or closed off, which puts more strain on the motor and adds to the static pressure.
I do know that you should be using spiral pipe with long sweep elbows and 22 ga minimum. You'd be surprised how sawdust being draawn through small diameter pipe can heat things up and wear holes quickly where ever there is a turn.
Also, don't forget a couple sweep stations on the floor.

rlw · Jun 13, 2005

I have an Oneida Air collection system in my shop. They will do a system design for you. I have their 2 hp system and am very pleased with it. Oneida is consistantly rated at the top in all the woodworking magazines. Definitely put in floor sweeps - I put one at each end of my shop.

tc35dforme · Jun 13, 2005

CFM = cubic feet per minute ... or in simple terms the quantity of air moved each minute.

The static pressure rating can be much more complicated. The way that this is measured and the way the rating is published has a a great deal of variation. In simple terms, static pressure is the amount of 'ooompf' that the fan has to push ( or pull ) air.

Free air ratings don't tell you anything when you applying it to a collection system and you need to see a performance curve for the fan to see how it works throughout its range.

When air is moved through a duct ( or pipe ), the friction between the air and the inside surface caused resistance measured in terms of inches of water column or w.c. The more air you try to pack through a small duct the more pressure you need.

What you need to be concerned with is the velocity of the airflow in the piping to keep the dust and particles entrained in the airstream. This rating varies based on the equipment served. Large chips ( planer ) requires higher velocity. Once you select the proper velocity, the airflow can be set to serve the equipment ( based on the size and configuration of the inlet assembly ), then the pressure calculated, then the fan selected...
...not so simple anymore /forums/images/graemlins/smirk.gif

Most equipment vendors will design and calc the system based on your equipment layout.