Dust Collection

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Subject: Re: 5000 cfm limit

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Message Thread:

5000 cfm limit

11/25/14       
Bob Member

I am looking to upgrade our dust collector.
We currently have a Dantherm S-750. Its a bit light for our Rover 30.
I am looking to put the most powerfuly unit I can use indoors. I know that there is a 5000 cfm limit placed on indoor units. Does this mean the unit can not be rated for more than that? Most units are advertized at a almost a free flow CFM. Most units with a load on them will actally be less. Can I put a unit rated at 6000 cfm that actally pulls less?

11/26/14       #2: 5000 cfm limit ...
Dylan Bayliss  Member

Website: http://www.cnc-tool.com

Bob, it all relates to the NFPA 654.
Google it and you will find information related to the Code. It might be worth spending the $42 to buy it as well. The code states the maximum you can put inside is a 5000cfm, open dust system. Different units have a different CFM's at different static pressure. You have to calculate the static pressure of your machine and the duct work and look at the fan curve to determine if the fan will handle the volume of air at the required static load. Your Rover 30 depending on its head configuration has the following requirements as per OEM manual
Air Req:30m/sec (5905fpm) 300mm Port
7634 meters cubed/hour (4493cfm) for Slots A and B
1940 meters cubed/hour (1191cfm) for Slot C
1940 meters cubed/hour (1191 cfm) for Boring operations

I would look at the S-1000
that pulls 5000cfm@7WG with a 400mm inlet, still a little low for OEM requirement but will probably do much better than the s-750 4500cfm@6" with 280mm outlet
We can offer this with dumpster bin $9,500 delivered. Questions, please call
314-504-8098
Dylan Bayliss
www.machineconsult.com

http://www.nederman.com/products/baghouse-dust-collectors/manual-baghouse-dust-collectors/s-series-bag-dust-collectors

12/1/14       #3: 5000 cfm limit ...
Curt Corum

NFPA 664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities 2012 Edition

12/1/14       #4: 5000 cfm limit ...
Bob

Thanks for your replies.

Is there a way of measuring CFM in the system or do I need to have my duct system calculated to find the resistance?
Would it be feasible to put in a unit capable of pulling more CFM but putting in a damper to limit it so I an get the most out of a system and keep safe legal limit?

12/1/14       #5: 5000 cfm limit ...
Dylan Bayliss  Member

Website: http://www.cnc-tool.com

You can measure the pressure and determine the Air Velocity/cfm based on the Duct size.

http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gages/Ser
iesDM-1000

In response to the last I believe the answer is no. The NFPA 664 is clear on the size of the unit. Most reputable Dust Mfgs that offer inside units will no longer sell you a unit bigger that 5000cfm. If you purchase one the assumed risk is on you and the mfg.
You might be able to use two different units to pull from the same machine, ie connect another 5/7.5hp to the machine to get enough cfm. I am not sure how this would relate to the 664 code and if there is verbiage for or against that.
Dylan

12/1/14       #6: 5000 cfm limit ...
Dylan Bayliss  Member

Website: http://www.machineconsult.com

another option for fpm
http://www.dwyer-inst.com/Product/AirVelocity/Windmeters/MarkIIWSI

then multiply by (88) to get FPM
regards
dylan

12/1/14       #7: 5000 cfm limit ...
Curt Corum

Bob, It is the dust collectors job to overcome the resistance of piping, etc., and pull the total CFM required. In this case, to create a velocity of 5,905 in a 12" diameter duct, the CFM would be 4,600. The resistance must be calculated properly.How many feet of pipe, elbows, flex hose, filter loss, and so forth. Lets say the final requirement is 4,600 CFM at 11.5" SPWG. You would select the dust collector that has those coinciding figures on a performance curve or chart. In case the resistance is a bit less than calculated
and the CFM is higher than necessary, a damper can be installed to purposely induce resistance and lower the CFM delivery. The velocity and coinciding CFM for this machine is much higher than that for typical woodworking machines, but then again, this is not a typical machine. Typical conveying velocities for woodworking dust collection range from 4,000 FPM to 4,500 FPM. It is the CFM in a duct that creates the velocity in feet per minute. There is no guessing as to resistance, it must be derived at accurately. All that I have mentioned pertains to a dust collector dedicated to this machine. NFPA 664, 8.2.2.2.1.6*, Where dampers or gates are used for individual equipment, the volume and velocity resulting from the operation of such dampers or gates shall not reduce the system velocity below the design minimum. Acceptable to use them for the instance I mentioned previously. Another good air flow instrument manufacturer is Alnor.

Curt

12/20/14       #8: 5000 cfm limit ...
cabinetmaker

Bob

I put a 15HP Dustek in just for our Rover on Dylan's advice. The fire dept and the insurance company has looked at it several times and said nothing. We do have it 30 feet from the nearest emergency exit.

I tried a 10hp on it, but the dust shoe is so large that it just could not get enough off the board. The 15hp is night and day. We are going up 12 feet with a 14" main to a 90" and then reduced to a 12" pipe and went straight to the machine with a 12" run elbowed down and hooked on.

We do still have left over chips stuck between the passes, but with return onion skin on the smaller parts its pretty clean.

We are planning on moving it outside this next month and put a VFD or soft start on it.

12/25/14       #9: 5000 cfm limit ...
Factory Owner Member

Bob,

I just recently purchased a building to move my operation into and was faced with the same dilemma.

I looked at large central systems and needing to be able to return the air back into the shop required spark detection as well as abort gates. For a system the size I needed it would have cost around $150k.

What I opted for were 2 20 hp cyclone units rated at 5000 cfm and an existing 10 hp cyclone. They are used in 3 different zones within my operation and this set up with good bag house after filters and cyclones was a fraction of the price.

I know that NFPA 664 is supposed to eliminate the possibility of dust explosions within the dust collectors, but honestly, in shops that have had good housekeeping procedures in place, in my 35 yrs. of woodworking I cannot recall one.

The ones we read and hear about are in grain mills and the like, not in architectural woodworking shops.

 

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