The motor on my main pump was replaced yesterday and now the pump puts out 10 psi less pressure than before. We inspected the impeller while changing the motor and it looked good - no sign of wear or damage. The pump is a Sta-rite single speed model PRA6F148L. The motor is 3450 RPM, 1.5 HP, 1.1 SF, 230 V. The replacement motor is the same as the original - AO Smith USQ1152, 48Y frame, 1.5 HP, 3450 RPM, SF 1.1, 230 V.
The pump seal was replaced two weeks ago so it was not changed. There is almost no noise from the pump/motor and there is no vibration. It seems to be moving about the same amount of water, but I can't really tell for sure. The flow coming from the eyeballs looks like it always has. There is a small air leak that was present before the replacement.
The inlet piping had to be cut so the pump could be moved enough to get the motor off and back on. After re-joining the piping length is the same as before.
The only possible explanation I can come up with that the motor is not rotating at 3450 RPM. I don't think it could be rotating backwards since it's 230 V, but I had the guy change the connections anyway and it made no difference in discharge pressure.
Anyone have any ideas?