I am attempting to get a good estimate of the flow-rate of my current pump, before swapping my single-speed pump motor for a 2-speed, but I am having trouble with the readings on my gauges. I purchased a Harvard vacuum gauge ( same make as mt filter pressure gauge & polaris test gauge ). Full scale is 30" Hg & the scale divisions are 1/2". The low end of the scale, however only has four major divisions, so I am assuming that it will not indicate a vacuum below 1". The filter gauge, graded in 1 psi divisions has an upper range of 60 psi, however the "peg" is 3 divisions below the 5 psi mark ( 2 psi min. ? ). The test pressure gauge, also graded in 1 psi divs. has an upper range of 45 psi. I my equipment pad was a "normal" configuration, there would be no problem with static head, and all gauges would sit on their pegs with the pump off. I my case, the filter gauge sits 2' below pool-surface level, and the pump gauge ( either pressure or vacuum ) sits 5' below surface level. Pump-off, the filter gauge reads 2-divisions off the peg while the vacuum gauge ( at the pump inlet ) sits on the peg. Pump-on ( clean filter ) the filter gauge reads 24 psi & the vacuum gauge sits on the peg. When the test-pressure gauge is substituted for the vacuum gauge, it shows 3 divisions off the peg static and with the pump on it wiggles off the peg ( 1/2 a division ). The formula used on this forum would indicate a return-head of 55.44'. The calculated static head at the filter ( assuming 2 divisions=2 psi ) would be 4.62', not 3'. The dynamic suction head, assuming 1 psi/div. 1.16', calculated, which I assume would be subtracted from the return head to give a total head of 54.28'. Plotted against the Tristar 3/4 HP curve, the flow would only be about 20 GPM. This seems to be way to low , as the return flow going through the 1" normal return & the 3/4" polaris feed-line is enough to cause the polaris to crawl along the bottom of the shallow end of the pool.
Comments and suggestions are appreciated.