Computing static pressure?

[cgallery]

If someone knew the CFM coming from a dust collector, and then knew the reduction in CFM after a cyclone was added, is this enough information to compute the static pressure loss of the cyclone?

[LCHIEN]

no. for one thing static pressure loss of a item is good only for one specific CFM.
as you increase the CFM the loss increases too.
gets very complicated...

[cgallery]

Thanks Loring, I was hoping you'd respond.

So when BP refers to his cyclones having 2.5" static pressure, is he probably just making a generalization at some "reasonable" amount of CFM? Here is a quote from BP:

I measured quite a few small shop cyclones and found my design at 2.4” static pressure was the lowest in the industry. The rest ranged from a low of about 3.4” for my design that most now use from my cyclone modifications pages to a worst case of 4.5” should you use an early Oneida-Air, PSI, or Gary MacIntyre cyclone without neutral vane.

Here is another question. Assuming a CFM from a dust collector (like 700), can I compute the drop in CFM by adding a cyclone if I know the static pressure that BP refers to? Like, I start w/ 1000CFM, then add a cyclone that BP says will introduce a 2.5" static pressure loss at that CFM, can I compute my new CFM?

I realize the math won't be perfect, just interested in approximations.

[iceman61]

Try this link:

http://billpentz.com/woodworking/cyclone/StaticCalc.xls

If you just want to read or don't have Excel:

http://64.233.167.104/search?q=cache...lnk&cd=1&gl=us

Hope this helps

[Garasaki]

Here is another question. Assuming a CFM from a dust collector (like 700), can I compute the drop in CFM by adding a cyclone if I know the static pressure that BP refers to? Like, I start w/ 1000CFM, then add a cyclone that BP says will introduce a 2.5" static pressure loss at that CFM, can I compute my new CFM?
.

This is possible, but only if you have the fan curve for the piece of equipment you are looking at. Pentz has some curves posted on his website. To do this, you'd take then CFM you (think you) have, find that on one axis, check the corresponding SP on the other axis, subtract the static pressure loss, find that on the SP axis, then go straight up until you intersect the curve, and the reading on the CFM axis should tell you what you want to know.

It's an approximation because as soon as you add the cyclone, increase the static pressure, change the CFM, the static pressure in the rest of the system changes.

So when BP refers to his cyclones having 2.5" static pressure, is he probably just making a generalization at some "reasonable" amount of CFM? Here is a quote from BP:

I would like to think Bill measured it, and yes he would have had to use some, hopefully consistant, airflow value - that is, I hope he had them all hooked up to the same DC.

Even so, because he does not give you the airflow value, it's impossible to equate his (hopefully) measured SP loss in the cyclones to any other system that would have a different airflow. It would be better if he reported the static pressure losses at different airflows.

Hopefully you are beginning to see why I don't think Bill is the god everyone makes him out to be.

[Garasaki]

Try this link:

http://billpentz.com/woodworking/cyclone/StaticCalc.xls

If you just want to read or don't have Excel:

http://64.233.167.104/search?q=cache...lnk&cd=1&gl=us

Hope this helps

The static calc spreadsheet will do you more harm then good. Stay out of it!!!

It calculates everything by assuming you have the target air velocity in the duct. This throws absolutely every calculation right out the window.

If you want to use that spreadsheet, the very first thing you should do is change the yellow "Target Air Velocity" to the biggest number you can think of. UNLESS you are trying to use the pink Optimum Duct Diameter value - you want "real" values in the cfm and target air velocity boxes then.