Will two 900 CFM ports equal one 1800 CFM port?

[Matt Hutchinson]

Later today I am going to inspect a single head 37" wide belt sander that I will likely purchase. From the info I can gather, these machines require around 1800-2000 CFM for adequate/proper dust collection. I want to upgrade my central DC to a 7.5 HP cyclone, but that can't happen for a little while. The machine I am looking at has a single 6" or 8" port for dust collection. In the meantime here's an idea, but I am not sure if it's actually going to work.

1.) Remove the single port that's in the center of the top of the machine and install two smaller ports that are space evenly across the machine's width.
2.) Run a small DC on each smaller port (two small DC units).

If each DC unit is pulling 900 CFM through each smaller port will this be the equivalent of a single 1800 CFM port? Do you think I could get good enough dust removal to get me by until I can spring for the large central DC unit?

Thanks!
- Hutch

[Peter Kelly]

I'd be concerned about the two smaller units not being cyclones. Widebelts generate a ton of dust and will quickly clog up filter media if the fines aren't separated out of the exhaust air.

Not sure that two 900 cfm collectors would generate the required airspeed either...

[Paul Wunder]

http://www.billpentz.com/woodworking...ne/ducting.cfm

Go to Bill Pentz's website and click on the link to his "static calculator" worksheet. There is a chart showing the maximum cfm that can be pushed through various duct sizes. The short answer is that 2 6" ducts from the collector all the way to the machine's hood can handle 1800 cfm. The longer answer has to consider additional factors: "true available cfm at the machine's ports from the dust collectors, friction loss at the ports, type of ducting and length, etc.

I am not an expert in this area. I just know enough to "get in trouble". Others, I'm sure will chime in to further help you.

[Matt Hutchinson]

Peter - That is certainly one of my concerns. I can see it now: zero performance due to a massive cake of sawdust on the filter.

Paul - The Bill Pentz site is something I have perused a few times. I will take a closer look at the ducting info.


Okay, so as I have been scouring this forum and the Bill Pentz site I now have a new question. This particular model of sander calls for 1600 CFM. Other similar models call for 1800-2000 CFM. In both cases these machines use only one port. Is it even possible to pull 1600 CFM thru an 8" duct even with a good cyclone? I have been having trouble finding clear answers.

Thanks!
- Hutch

BTW, I stated each port would collect at around 900 CFM, but the DC units would be 1.5 HP collectors. I am estimating that the actual CFM at the machine port would be around 700-800 CFM if the dust collectors were placed right next to the sander and 6" rigid duct was used.

[Rod Sheridan]

Hi Matt, yes you can have 1,600 CFM through an 8" duct, at higher velocity and losses than a 10 inch duct.

As others have said, sanders generate large volumes of dust that will in very short order overwhelm a small single stage collector............Rod.

[Paul Wunder]

http://www.nordfab.com/view/assets/l...uct_system.pdf

THIS CHART FROM NORDFAB MIGHT HELP

[Jim Neeley]

Matt,

Running 1600 CFM through 8" straight duct has the air moving at 4584 FPM (a good speed, 4000 is a typical target). The total pressure drop through 40' of straight duct would be 1.56" WC.

Running 800 CFM through 4" straight duct would require the air to move at 9167 CFM. With a square-edge hood and 40' of straight duct, the pressure drop would be 17.92" WC (yes, 17.92). Few, if any, commercial DCs will flow 800CFM at 17.92" WC; none in our hobby/light commercial markets.

Please remember that it takes *four* 4" ducts to equal the area of one 8" duct and even then, the pressure drop will be higher due to the transition from one 8" to 4" and the additional surface area of the pipe.

If you installed four DC's and four each 4" ducts the velocity would be back down around 4528cfm and 4.75" pressure drop, more attainable by "our-type" DCs.

If you want to play with the numbers, download Bill Pentz's staticcalc.xls and you can play with the numbers to your heart's content.

Jim

[Matt Hutchinson]

Well, it sounds like it would be a fool's errand to set up a couple single stage DCs for this purpose. This was basically a brainstorm that needed input from those with more experience with this type of thing, and I think I got my answer (the answer that I expected ). Thanks guys for all the help. If I end up getting this wide belt sander then I will just plan on waiting to put it into service until after I get my new central cyclone system.

- Hutch

[David Kumm]

Matt, it isn't wrong to use single stage collectors with a wide belt if you have the proper bags- material and size. While a good 5 hp cyclone will pull 1600 cfm through an 8" port, you don't usually want cartridges as even the cyclone will allow much dust through to the filters. Many wide belts use bag filters as stand alone collectors. you have to hit the bags periodically to get the cake off but easier than cleaning a cartridge with compressed air. A 5 hp two bagger or better yet three bagger will work just fine. Dantherm, Coral, dustek, and Belfab are all commercial baggers that can be fitted with bags suitable for sanding dust. I run a 7.5 hp cyclone with four Wynn nano filters but don't use it with the wide belt. Dave

[Matt Hutchinson]

David,

You know, now that I think about it I have seen single stage DC units attached to sanders. Looking back a few years, I worked in a factory that had a dedicated system for one of its sanding machines. When you say "bags suitable for sanding dust" what exactly do you mean? Thanks!

- Hutch

[David Kumm]

David,

You know, now that I think about it I have seen single stage DC units attached to sanders. Looking back a few years, I worked in a factory that had a dedicated system for one of its sanding machines. When you say "bags suitable for sanding dust" what exactly do you mean? Thanks!

- Hutch

Beane bags for one. J.R. Rutter put me on to them. He uses them on his Dantherm dedicated to his sander. Dave

[Curt Harms]

Here's another source for custom bags. I got a bag from them years ago, it worked well. I was distraught because it didn't puff up, just kinda hung there. We were all ignorant at one time, right?

http://www.americanfabricfilter.com/