In designing tests for the six sample collectors we received in the shop, we wanted to make sure that the numbers reflected how the collectors would perform in a real shop. The first thing we did with these factory fresh machines was to season the filters with 10 lbs. of diatomaceous earth (a small particle size substance similar to wood dust; we got ours at a pool supply store because it's often used in pool filters).
With properly seasoned filters, we were then ready to begin our real-world tests. The first test we did was to generate fan curves, the industry standard in comparing dust collectors. In order to do this, we hooked each machine up to a 10' run of pipe that was 6" in diameter (5" for the General International cyclone). Then we took a CFM measurement and a static pressure measurement. We proceeded to decrease the opening diameter at the end of the 10' pipe by 1" increments, repeating the CFM and static pressure measurement after each decrease. The decrease in diameter increases static pressure and makes each machine work harder.
Finally, we were able to generate a fan curve for all of the machines. Keep in mind that these fan curves may not be the same as the ones reported by the manufacturers, as there are a variety of methods used for generating them, and most are generated with clean filters with little to no back pressure.
Then came the hard part: hooking each machine up to the same 2" flex hose, 4" flex hose, 5" flex hose and central system. The key here is that each machine's inlet is at a slightly different height. Rather than move a monstrous 40' long central duct system up and down, we decided to use the lift at our loading dock to raise and lower the machines into position. It made things easier, but measuring, re-measuring and verifying our measurements was still hard work.