Difference in filter pressure vs wet end pressure? Should they be different?

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MitchRyan912

MitchRyan912

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Jul 21, 2015
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Madison, WI
I had a pool guy come out and take a look at my mess of a pool (Bad motor --> cavitation damage = useless wet end?), and he was rather stumped as to why I keep blowing up motors and having problems. He did note that there was what seemed to be a lot of pressure at the wet end (25 psi) versus what was at the filter (18 psi.) He seemed to think that could be part of the problem, or that there was the possibility of the (single) return line being plugged up, making the pump have to work much harder.

Does any of that sound plausible?
 
Where specifically was the pressure measured at 25 psi.

Can you post a picture of the whole system?

See what pressure you get at the wet end with the multiport on recirculate.

Measure volts and amps at the pump while under load. Use a true rms meter if possible.

Also check the frequency of the incoming power.
 
FWIW, the above reading was from when the motor was first installed, i.e. everything working properly. Something has happened since then, and it's not able to get the pressure up that high anymore, only about up to 15psi.
 
What is the current vacuum pressure? Does the wet end pressure match the filter pressure?

Check volts and amps at the motor under load with a true rms meter. Check line frequency.
 
The motor is drawing way more amps that it should, since it started acting up. It'll draw about 15A on high speed and 7A on low, which are way above spec for this motor. That's both under load and with the pump disconnected from any plumbing.

I don't believe I have anything to check the line frequency. I'll have to borrow the clamp ammeter I have access to, to see if there is a frequency meter on it.
 

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The heat could explain the extra amps. Something isn't right. Does the shaft turn freely?

If the shaft turns freely, I would suspect that your impeller is too big for the motor. The picture that you posted of the impeller looks like it's a big impeller. What is the part number stamped on the impeller?
 
It's labelled as a 310-7510, which is a 1 HP impeller. It's what came with the pump, that and a 1.25 SFHP motor. I think I've been over this before, but the new motor is a 1.2 SFHP motor (3/4 HP x 1.6 SF.) As far as I know, that should be the correct size impeller.
 
If the pump has a large service factor, like 1.65, then the impeller could be oversized. It looks like a big impeller. An oversized impeller seems most likely if the shaft turns freely.

The partial number I see in the picture is 4140, which looks like it might go to a three hp pump.
 
Now that I look around Waterway's parts site, I think that there is at least 2 pieces of plastic that are ultrasonically welded together, and that the 4140 is just the part number for that piece of the impeller. The 4140 part could be the same in each size impeller, but different pieces welded together make up different impellers. See the two part numbers here:

large-champe-110-impeller-assembly.jpg
 
It should come with the correct impeller. Perhaps they made a mistake and put on the wrong impeller. The impeller looks big in the picture. The pressure matches a bigger impeller. The amps and excessive heat match an oversized impeller.

Get a new impeller and compare them.

I think that it's either an oversized impeller or an electrical power quality issue. Can you check the frequency of the power?

Can you post a few pictures of the whole impeller from different angles?
 

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