Motor slowing down

My F&W 3/4 hp motor has been sitting all winter and I just hooked it up yesterday to irrigate the garden. It started fine but after several minutes it began to slow down. I stopped it and waited only to have it happen again. I checked and it is wired for 220 and there is 220 coming to it. Whether it is significant or not, I'm not sure, but there is no continuity between either line and ground. However there is continuity between L1 andL2, although it doesn't trip the circuit breaker when I turn it on- it just runs for a few minutes and then begins to slow down. As it is slowing down I checked the centrifigal switch and it was open as it slowed down. Any ideas would be appreciated. Any way to check or lubricate the bearing without taking it apart? Thanks, burlap

Reply to
eversfm
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It is scary how little you know about it. It is also very dangerous for yourself. Take your motor to professionals.

Reply to
Virus

Bearing screwed? Or the switch. Is it a true split-phase?

Reply to
The Real Andy

No continuity to ground from either line terminal is good !! For it to slow down there would have to be some mechanical friction or possibly "flooded suction" ie. no restriction in the pump output. For an installation previously working that is unlikely. For an installation that has been in place for years and not used for a while it can happen that rust or corrosion will build up on the shaft where it enters the seal in the pump. Or deposits are formed around the impeller. Either will present an extra load on the motor. If you cant monitor the current for the motor and compare to the name plate, I would recommend dismantling and inspecting the foregoing. If you havent had it maintained in the last 5 years that would be a good start :-)

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Cheers ......... Rheilly P

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Reply to
Rheilly Phoull

The motor is a 94J107 capacitor start dual voltage motor. It does have the shallow well ejector package which contains a venturi type plactic tube that can get plugged. I'll put an ammeter on it and if it matches the plate I'll take it apart and check the ejector and the bearing for any wobble. Thanks for your help and patience. Having been in the greenhouse and farming business for many years, if a furnace goes out when it's cold or a fan doesn't work when it's hot we couldn't afford the luxury of waiting to get it fixed. Every time an engine doesn't start when the key is turned or nothing happens when a switch is flipped I try to get things going. Motors I know the least about because the conventional wisdom is "if it doesnt work throw it away and get a new one". Getting a motor repaired in a timely manner where I live is difficult. Thanks, burlap

Reply to
eversfm

A blocked injector, or any kind of restriction on the inlet normally leads to the pump cavitating and if anything, running faster, similar to what happens when you block the suction on a vacuum cleaner.

I'd be looking for a dodgy bearing (at either end) or rust around the seal, or a small stone caught against the impeller.

Reply to
Poxy

I put an ammeter on it and it draws 7 amps for a bit but soon you can hear it slowing down and see the amperage going up. It then peaks to 15 amps before I turn it off. The sprinklers seem to be putting out the usual amount of water while it is running. Thanks again, burlap

Reply to
eversfm

Try these:

  1. Disconnect the pump and see if the motor itself slows down or if the no-load current increases. If it does slow/increase current by itself then either a bearing or bush is stuffed or the insulation between windings is breaking down. The insulation can break down (or be tracked over or around) if it has been exposed to moisture. Seals and gaskets can deteriorate over time. When a motor is running often and stays warm everything is fine. But when it is shut down and cools off moisture air is drawn in past the crook seals. In cold conditions this condenses inside. Have it rebuilt or replaced.

The above also applies to alternator windings in generators, especially when they are left sitting on the dewy ground after being run. The mositure gets sucked in as it cools, condenses on the walls of the motor body and dirt or contaminants wind up trickling to form a pool in the bottom of the housing. I ruined two good and expensive alternators (6 and 10 kVA) this way till one of local cockies told me to "lift ert up to make ert last".

  1. If after 1 all seems OK then, with it still disconnect from the pump, apply a load to the shaft using a block of wood or some other safe method of applying braking torque. The current should increase and the motor speed and current recover to the no load condition as soon as the load is removed. If it doesn't then the motor is again at fault.

  1. Check the motor cooling fan hasn't walked along the shaft and then decaptiated itself on the housing causing the motor to overheat.

If the motor seems OK after doing all this then pump looks to be the culprit. The sealed bearings are probably stuffed and heating up under load, or the impeller has chewed out the housing, assuming they are both plastic. While the plastic is cold the parts slip past each other but friction soon heats them up and they drag as the material softens.

My guess is the flow rate is fine because the pump is running well under its rated capacity and there is a pressure regulator in the output. So the regulated pressure masks the drop in pump capacity.

Hope this helps.

Reply to
David, not to be confused with

Is this greenhouse and farming business a hobby? A professional outfit keeps spares, when a motor goes bung, you change it for the spare so you can get the faulty one fixed. A professional knows that a pump, or any other important equipment could break them if it breaks is always prepared with spares.

Reply to
two bob

It was a business and all our greenhouses had redundant systems-if one went out we were okay but they still had to be fixed. However you would be talking3-4 days to have a motor repaired 30 miles away. Why wouldn't I want to fix it myself? Most of the time I managed okay with mechanical and electrical problems- but I've never had this problem before. And if you're learning from experience sometimes the curve is pretty steep. Thanks,burlap

Reply to
eversfm

You do realise that you are conversing with a septic tank ??

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Reply to
George W. Frost

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