I would like some information on dust collection. I have been reading as much as I can about the subject and I have found myself perplexed about Static Pressure and dust collection systems.
First, I understant that most duct collection units are rated for static pressure, and I am curious about how the reliability of these ratings.
Second, am I correct in stating that when setting up a dust collection system, it is a balencing act between CFM (cubic feet per minute) and static press? Also, does a Cubic Feet per Minute rating have little value if there is not enough static pressure in a particular main line or branch line to keep particales suspended? Is a Static Pressure rating more of a consideration than CFM? Lastly, how does one prevent static pressure loss?
Third, is there a source out there that I might be able to read that may help me to answer these questions? Thanks Jim A&H
Replies
Woodshop Dust Control: A Complete Guide to Setting up Your Own System by Sandor Nagyszalanczy seems to be the bible for dust control (That's a link, go ahead and click).
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Another proud member of the "I Rocked With ToolDoc Club" .... :>)
Actually, all you care about is the CFM, under the conditions you are running your system; the static pressure is useful only in helping you to evaluate that. Unfortunately, the information you need to determine that is usually not provided. The static pressure that they quote is usually under conditions of zero flow, possibly the measured value that is closest to completely useless that they can give. A vacuum cleaner can usually provide a static pressure at zero flow much better than any DC, and a vacuum pump as used for veneering can pull a static pressure much better than that, but it is 100% worthless as a DC. CFM ratings might be more useful, but they are usually quoted for the blower with back pressure at all -- sometimes without even the DC itself and only the blower.
What you need is the blower curve that plots the flow possible through the system at various back pressures. Then you need to consider the diameter, length, and path of your duct to evaluate how much back pressure will be caused. Check the curve to see that you will have adequate flow through your duct, and you are all set.
Bill Pentz's website provides a "static calculator" spreadsheet that will let you estimate the pressure drop through your duct at a given flow rate. It is a wonderful source of other info, such as the linear speed the air must go (CFM / duct cross sectional area) to prevent dust from settling out and clogging the duct. Maybe if enough people demand it, more manufacturers will provide the blower curves we need. Here's Bill Pentz's site:
http://billpentz.com//woodworking/cyclone/index.cfm
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