I am at my wits end with my bench. I calibrate it regularly and have had very consistent results for a few years after I changed the motors. I now run 8 light house motors. This is a liquid manometer rotating orifice bench.
Suddenly recently I had a few sets of heads that didn't flow the same as I typically see. Flow was down about 6% across the board, both intake and exhaust. I have always checked for leaks before I test and there are none now nor were there before. I suspected a leak at the change over valves but that was not the case. I took the top off and looked in the chamber for damage, looked good.
I recalibrated with PYS plates in all the ranges and my flow is back to normal but still the mystery is what happened to drop the percentages shown on the inclined manometer causing me to comp the numbers in the calibration. Looking for ideas. All help appreciated.