Motor slowing down

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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


Re: Motor slowing down


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

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Re: Motor slowing down



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

Re: Motor slowing down



The Real Andy wrote:
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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


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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.




Re: Motor slowing down


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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.





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two bob wrote:
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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


Re: Motor slowing down


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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 :-)
--

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

Where theres a will, I want to be in it.



--

Re: Motor slowing down





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
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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".

2.
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.

3.
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.



Re: Motor slowing down



"David, not to be confused with the other Davids."
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You do realise that you are conversing with a septic tank ??





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