dust collectors...

[Mike Kees]

Is it possible to have to much power in a collector? What I mean is all the formulas to figure out c.f.m. and static pressure to assure that your system will work focus on having enough power. So what I am wondering is in my example a 3 h.p. cyclone will work but should I buy a 5 h.p. for future expansion. The size of the ducts seem to me to control actual c.f.m. more than collector (after you get to the point of enough power to do the job). Am I correct in this assumption or just barking up a tree again. I know there are guys on this forum with far more knowledge about this than me,please fill me in. Thanks in advance for any help.

[Lee Schierer]

Size affects your energy bill. Duct work size is very important as you need a certain velocity to move particles of a given size. Here is a handy calculator for determining the velocity of the air moving through a duct. LFM calculator (http://www.engineering.com/calculators/airflow.htm) I'm not aware of a chart showing what feet per minute of flow rate is needed to move planer chip versus saw dust versus sanding dust.

[Kent A Bathurst]

If you have legit plans to expand, then I would get the size needed for the final solution.

You duct it as if you had the future tools - leaving a stub pipe up there somewhere, open to the world, to keep the system balanced. Sucks up air, dust, flying insects, and any stray sparrows.

I have done this a jillion times in industrial applicaitons, where I'm driving 150hp - 250hp motors on the blowers. :eek:

The problem is this: If you size the system correctly for today, then your pipe diameters are all wrong for when you need to expand at the other side of the shop. You don't just replace the DC, you have to replace the piping as well.

Lee is correct about the electron $$$. But the cost to rework the system outweighs that, IMO.

[David Kumm]

Take it from someone who went from 2 hp to 3, then 5, and finally 7.5 hp systems. 5 hp with 8" and 7" mains is a pretty good tradeoff for a one person shop with some larger machines and some distance to run. When you get to runs over 30ft and 20+ drops you might find the need to go larger but 5 hp handles most hobby shops. If you get all the piping right, have machines with efficient dust shrouds, plenty of filter area and shorter runs you can make a 3 hp 14" impeller work but the 15-16" 5 hp is pretty hard to screw up. My shop got too large and machines too old for the 5 hp system. To compensate for the 8 and 7" mains ( normally a 7.5 hp will have 9-10" ) I substituted a higher pressure blower that needed the additional amps but pulled better through the slightly undersized pipes. Dave

[Michael W. Clark]

If you know you will eventually want the larger one, get it now and the overall cost will be less. Some people do well with a 2HP cyclone, but a 3HP is the smallest I would go if buying a cyclone system for the home shop. If you buy the 3hp one now, you could always add another 3hp unit in the future. Two units would likely cost more than one larger unit and you have more to maintain. Of course, it also depends on what you are collecting from. A bagger with more filter area is better for a sander, or get a high efficiency cyclone and filter.

Yes, the duct losses will affect airflow. You can pull too much air through a cyclone and negatively affect performance. If you think this is likely, just install a blast gate at the inlet to the cyclone (not exactly on the inlet, but several diameters away) and keep it partially closed to reduce the air volume. You can also choke one too much and cause the fan to surge.

Like Kent said, you typically plan your system for the future on larger industrial systems because they use a tapered duct system. Adding collection points means reworking the ductwork to keep the velocity correct.

ACGIH has a table of recommended duct velocities for different applications. Not sure if you can find the image or if you have to buy the book. I have a couple of different editions, basically, sawdust is conveyed between 3500 and 5000 FPM depending on the nature of the dust. You can use lower velocity on the fine dust, higher velocities as the chips get bigger and wetter. NFPA has minimum velocities too and sometimes references ACGIH.

[Jim Andrew]

I have read quite a bit on Bill Pentz website, and as I recall, he first used 3hp motors, and when he used the 15" impeller, the amps tested just slightly above what a 3hp motor would operate at for long life, so he switched to a 5hp motor and it drew just enough amps to operate the blower. Now that Bill and Clearvue have gone to 16"impellers, they are using a bit more power, but not too much for the 5hp motors. Interesting to check out the Grizzly Christmas catalog, the 3hp cyclone specs list the impeller at 151/2". Alsointeresting is that the bag units have smaller impellers. Could someone explain the difference?

[David Kumm]

Bag units usually have smaller impeller because there is no pressure drop due to the cyclone. 2-4" of extra SP to overcome. Filters also create additional SP so if the area of the filter or the media create more SP than a competing unit, the motor can be smaller. I think the Grizzly 3 hp motor has an amp draw closer to a 5 hp ( if I'm remembering right). Also, an increase in size of a curved blade impeller doesn't increase cfm at the higher working pressures of many systems as much as an increase in a straight blade. Dave