Pump Mystery

[stev32k]

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?

 

[Bama Rambler]

It seems likely that the replacement motor has more slip than the original but that's rare. Adding a fitting to the system could have increased the suction head a little, and maybe the two things together would account for the lower pressure.

 

[mas985]

Slip of the motor would not be more than 5% or it would overheat (high load) and not less than 3% if the impeller is the same (low load). More than likely it is probably the pressure gauge or the plumbing changes fixed something that was causing higher pressure.

 

[duraleigh]

My bet would be on the pressure gauge. That's a really big jump for it to be an actual change.

 

[stev32k]

Just an update. Today the pump will not run. Tried to turn it on this morning and it made a slight noise for just a split second then nothing. Tried turning it off and on several times still nothing - makes no sound it just sets there. I opened up the inlet strainer and I can feel the impeller and it turns freely.

My first thought was a loose connection or bad wire. So I unhook the piping to get at the back and check all the connections and wires and can't find anything wrong. Then I turned the breaker on and check the voltage and it seems to be correct, but the pump still does not run.

I've sent an email to the mfg. (AO Smith) explaining the situation and I'm waiting to hear back.

So now I have a pool full of leaves and debris from Isaac and no way to clean it out.:grrrr: Guess I can get ready for another session of shocking the pool when the pump problem gets resolved.

 

[Pointyhead]

Just shooting from the hip here, but sounds like you might have taken a lightning strike that took out an already weak pump.

 

[stev32k]

Actually it turned out to be a bad connection. I didn't find it the first time, but the second time around I cut off the original connectors, stripped the wire, put on new lugs, and the pump started up. The original lugs didn't look bad or corroded and they seemed to be crimped okay so I don't know what the problem was but it's fixed now (I hope).