Well, in retrospect, I'm not totally sure I do either (semi-old post in old thread recently resurrected with a new post). I've done some reading and thinking about pumps since then.
I think what I was trying to say was "How hard could it be to measure output from a pump, though a measured length of tubing, tubing outlet at the same height as the pump outlet?" (Was thinking about just timing how long it takes to move a gallon, for instance.)
But even that doesn't allow for the residual pressure (positive or negative) coming from the relative elevation of the reservoir (or whatever you want to call the container that's feeding the pump). I'd guess the best you could do to minimize this would be a container with a very large cross-section, with the container outlet near the water surface and the pump inlet on that same level. I'd also guess that another way to do this would be to measure the rate from reservoir through the pump and tubing to the outlet without turning the pump on. Still not right as an unmoving rotor is going to present some resistance (much more if it's a closed rotor). Maybe remove the rotor for this measurement, try to keep pump inlet pressure slightly positive, and then subtract this flow from whatever the pump produces when running.
So - do I think WCP actually did any of this? I dunno. Probably not, though... IMHO the best we can hope for is that they used the same reservoir source setup for all the pumps in their spreadsheet so at least those numbers are comparable to each other. Might be a forlorn hope at that.
|