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Originally Posted by brucepts
Rick, If you recall we did a really non-scientific study about 2 years ago over on the flowbench forum on the "plate on top of the bench theory" and how close numbers from various commercial and homebuilt benches actually came. This included the "Mega $$$ Flowbench" at Ford Automotive. .
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Some flowbenches will show close to the "expected/calculated" flow when an orifice is flowed on top of it, others will not. Most of the benches in the test were "calibrated" already by your plates tested in the same manner which would give very similar results. The way a flowbench is built internally has a big influence on the air that will flow thru an orifice on top. How big is the plenum, where is the depression/pressure tap, where are the d/p taps, thickness of the top of plenum, diameter and shape of entry hole into plenum ... etc etc. Too many variables that CAN influence not only the reading, but the actual flow thru the orifice. A bench with a head on a 4" adapter distributes and slows the air significantly before entering the plenum, yet with a orifice mounted right on top creates a much higher velocity right into the plenum. What if someone has a pitot bench and the pipe IS the plenum, would it work then?
Why won't the same orifice inside different size pipes give the same flow/DP? Because the surrounding area influences the flow thru the orifice.
Quote:
Originally Posted by brucepts
There are a lot of flowbenches now being "calibrated" to cousins of those original plates around the world. This allows those users to compare their bench readings to the original set of plates, so in effect there is somewhat an industry standard being used already. Some well know head porters are also using those plates to compare their numbers. I know there is even a commercial flowbench product using those same plates for comparision now.
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A lot of people do a lot of things, that doesn't make it correct. SF provides an orfice plate to "test calibration" and they know how their design works with their plate to show there are no problems with a bench. You should never change your numbers on a SF bench based on the orifice "cal test". This cal method may work in a lot of benches, but not all. How would you know? Shouldn't something used to calibrate ALWAYS be correct?
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Originally Posted by rookie
Would the Flow Quick eliminate all these variables?
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No, it mostly eliminates measurement errors and speeds testing by eliminating manometer settling time.
Rick