Electric Motor/Pump Help Needed

[d2dave]

Any electric motor experts here.

I have a pump which came out of the glycol beer system at my footy club

This pump is a submersible type with a float switch.

It was not working so they got a new one.
It was very expensive so I thought I would have a look and see if I could fix it so we could have it for a spare.

Here is the problem. It hums but does not run. I pulled the top off and it had a capacitor. I suspected that this might be the problem, so I tried another and bingo it worked.

However the one I tried was a lot bigger, as it was one I had lying around.

So I ordered a new one the same size as the old one and it does not work, just hums.

The original is 8 uF. The test one I used is 20 uF. I had the new 8 uF one tested to make sure that it was not a dud.

I then did a currant test. The label says it uses 2.8 amps. It was drawing around 2 amps. This is with no load as it was not pumping liquid.

Any ideas anyone?

[simmo]

Hi Dave, i'm not an expert but sounds like a single phase motor they have often have low starting torgue, your bigger capacitor is probably helping with that.

Example if you spin start the motor with your finger or a blast of air in the suction and it runs ok starting torque is the problem usually means the bushes are dry, (small motors often have oil impregnated sintered metal bushes , not ball bearings they get dry. Or if ball bearings they might be knackered.

Open up the motor and check those things first, the running current doesn't sound too bad, you could check the load current by putting it in a bucket of water and run it, but restrict the flow to about 60% of the cross section of the discharge to mimic some system resistance. cheer simmo

[d2dave]

Thanks. The motor does have a bit of resistance. The hole to the impeller is a bit small to get fingers in so I put a socket on it.

There is more resistance than I would normally expect, but it feels like the seals, not buggered bearings.

Although a bit tight, it feels smooth, which is why I suspected the seal.

I was wondering if the bigger capacitor was over riding the tightness. I thought I would ask here in the off chance there is a motor expert.

I shall pull it down further and investigate.

[Fluids]

Dave ... if memory serves me correct, increasing the cap' size will also increase the current in the start windings ... :eek:

The drag will likley be from the bearings if the pump has any sort of age on it ... the pump should (for that application) be running a mechanical shaft seal (not lip seal/s) ... IF it's lip seal/s maybe they have swollen over time from the contact with the glycol. Mechanical seals don't suffer this malady.

Current draw is proportional to volume pumped ... you'll only see max' current at max' flow rate. The 2.8A quoted is MAX ... spinning in free air it should be WAY less than this.

In the industry for submersible pumps we generally work on an 8500Hr life expectancy ... 24Hrs/Day 7days/week 52weeks/year = End of life.

Before doing anything you need to check the winding insulation resistance (megger test), and then the start/run winding resistances (against published figures - and sometimes these are impossible to obtain). If the stator windings are comprimised in any way there's no point proceeding with a repair ... motor's stuffed/on the way out.


Cheers!

[d2dave]

In the industry for submersible pumps we generally work on an 8500Hr life expectancy ... 24Hrs/Day 7days/week 52weeks/year = End of life.
Cheers!

This one has done a lot more than the above. Estimate 87,000 hours.

[d2dave]

Ok, I pulled it down today. My original guess was right. It was the seal causing it to be tight. The bearings are ok, although if I repair this I will change them.

With the seal removed I connected the new 8 uF capacitor and it runs perfect.

Kev, it is a mechanical seal. The only reason I could see for it to be tight is this.

The part of the seal that is fixed to and spins with armature has a big spring. This seal is double ended. There is a ceramic seal at both ends of this spring

Now this part that slides over the armature's shaft and spins with it, was very tight and pushing hard against its opposing face

I cleaned and lubed the inside part of the seal and reassembled it. The pump now turns with minimal resistance and it now works ok.

My next problem is trying to find a seal without having to mortgage the house.

Do you have any contacts for non genuine? The label on the pump says STA-RITE, model CSM 240 VF.

Although it has nothing on it to suggest it, it appears to be an Onga. It is identical to the one on the very left in the pic.

http://www.onga.com.au/objectlibrary/704?filename=Sta-Rite%20CSM%20Range%20-%20Hydraulic%20Performance%20%28Jan%2005%29.pdf

[Fluids]

Cool. It's a double/back-to-back mechanical seal ... usually these run in an oil bath ... or at minimum they are water lubricated ... carbon/ceramic seals needs some kind of lubrication and cooling ...

Sta-rite (USA) purchased Onga Australia some years back ... product quality imho went to the pack and we haven't sold Onga product for a long time (by my standards it's turned to ****!). The pump isn't manufactured by Onga ... looks like one of the many O/S manufactured units that the majors buy and rebadged or have made under licence agreements ...

You could try an Onga dealer, but be prepared that the seal could be rather expensive, or if you have access to a GOOD pump shop, take the old seal in and get them to match it up (if they have a range on the shelf). Failing that, some bearing places do mechanical seals, or find a dedicated industrial seal supplier.

If all else fails I can probably source one for you ... maybe. Let me know if you don't have any luck locally.

... and 87,000 hours ... that's just nuts !! :eek:

Cheers