Have you ever felt a little confused when trying to compare or evaluate the published performance data for various electrified equipment? Don't feel badly. The data is often confusing and there are usually caveats about the measurements that the manufacturer does not publish with the data. As an example, most of us are familiar with the “actual” versus the “developed”
horsepower ratings of some consumer power tools and machinery. It seems that some manufacturers are now even using “peak” horsepower in the ratings of air compressors, which has little or no meaning. Recently, I've looked into some of the various rating systems used by manufacturers of dust collectors. The “CFM” rating of a dust collector may or may not provide you with a useful indicator of performance. The “CFM” rating represents the Volume Flow Rate (VFR) of air, usually in cubic feet per minute (cfm) that the collector allegedly moves. It's important because the dust collector requirements for most machinery is expressed in VFR. For example, a 6" jointer may require 350 cfm and a large planer may require 700 cfm. The VFR rating of many dust collectors is a so-called “free flow” rating. This is the VFR into the fan of the collector, without the exhaust bags and without the inlet filter duct fitting. In other words, this is the rating of the dust collector fan without the other collector parts. In my book, this information is of no use to anyone.
Every dust collector has a VFR performance curve, similar to those shown below. As the flow rate is reduced (with longer pipe runs or restricted inlet flow), the suction at the inlet of the collector increases. The suction is usually expressed in inches of water. A collector with about six feet of pipe or hose with clean bags has about 2 to 4 inches of vacuum at the inlet. As the inlet hose or pipe is lengthened or intake flow restricted, the VFR decreases and the vacuum increases, and the collector performs at a
different point on the curve. Henceforth, we will rate Woodtek® collectors in
terms of Useful Volume Flow Rate (UVFR) and Collector Inlet Vacuum (CIV) at this flow rate. The UVFR is the flow rate (in cfm) with a six foot piece of smooth inlet pipe (of the same diameter as the inlet) installed while the collector is operated with clean dust bags. This is what you can reasonably expect when you hook up the collector to your machine! (By the way, our
Woodtek® UVFR performance shown in the table beats the heck out of some very popular brand collectors).
I challenge others in this industry to adapt the same measure of dust collector performance so the performance numbers have
meaning to the consumers who rely on our representations in purchasing our goods.
Best regards,
John Wirth
President and Owner
Woodtek® Collector Useful Volume Collector Inlet Vacuum
Performance HP Flow Rate ~ cfm† ~ in. H2O
864-381 (4 bag) 3 1180 4.0
102-023 (2 bag) 1-1/2 730 3
805-930 (2 bag) 2 790 3.6
802-124 (2 bag) 1 400 2.0
864-367 (1 bag) 1 380 2.0
911-047 (Mini) 3/4 250 1.0
† Useful Volume Flow Rate (UVFR) is flow rate with a 6 foot piece of smooth
inlet pipe, of the same diameter as the inlet, with clean dust collector bags.
* Volume Flow Rate (VFR) is free flow rate without bags or inlet fittings.
Toward Meaningful Dust Collector Flow Ratings...
horsepower ratings of some consumer power tools and machinery. It seems that some manufacturers are now even using “peak” horsepower in the ratings of air compressors, which has little or no meaning. Recently, I've looked into some of the various rating systems used by manufacturers of dust collectors. The “CFM” rating of a dust collector may or may not provide you with a useful indicator of performance. The “CFM” rating represents the Volume Flow Rate (VFR) of air, usually in cubic feet per minute (cfm) that the collector allegedly moves. It's important because the dust collector requirements for most machinery is expressed in VFR. For example, a 6" jointer may require 350 cfm and a large planer may require 700 cfm. The VFR rating of many dust collectors is a so-called “free flow” rating. This is the VFR into the fan of the collector, without the exhaust bags and without the inlet filter duct fitting. In other words, this is the rating of the dust collector fan without the other collector parts. In my book, this information is of no use to anyone.
Every dust collector has a VFR performance curve, similar to those shown below. As the flow rate is reduced (with longer pipe runs or restricted inlet flow), the suction at the inlet of the collector increases. The suction is usually expressed in inches of water. A collector with about six feet of pipe or hose with clean bags has about 2 to 4 inches of vacuum at the inlet. As the inlet hose or pipe is lengthened or intake flow restricted, the VFR decreases and the vacuum increases, and the collector performs at a
different point on the curve. Henceforth, we will rate Woodtek® collectors in
terms of Useful Volume Flow Rate (UVFR) and Collector Inlet Vacuum (CIV) at this flow rate. The UVFR is the flow rate (in cfm) with a six foot piece of smooth inlet pipe (of the same diameter as the inlet) installed while the collector is operated with clean dust bags. This is what you can reasonably expect when you hook up the collector to your machine! (By the way, our
Woodtek® UVFR performance shown in the table beats the heck out of some very popular brand collectors).
I challenge others in this industry to adapt the same measure of dust collector performance so the performance numbers have
meaning to the consumers who rely on our representations in purchasing our goods.
Best regards,
John Wirth
President and Owner
Woodtek® Collector Useful Volume Collector Inlet Vacuum
Performance HP Flow Rate ~ cfm† ~ in. H2O
864-381 (4 bag) 3 1180 4.0
102-023 (2 bag) 1-1/2 730 3
805-930 (2 bag) 2 790 3.6
802-124 (2 bag) 1 400 2.0
864-367 (1 bag) 1 380 2.0
911-047 (Mini) 3/4 250 1.0
† Useful Volume Flow Rate (UVFR) is flow rate with a 6 foot piece of smooth
inlet pipe, of the same diameter as the inlet, with clean dust collector bags.
* Volume Flow Rate (VFR) is free flow rate without bags or inlet fittings.
Toward Meaningful Dust Collector Flow Ratings...
