well pump cycles on and off with constant power

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BAPOER

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I was helping the brother in law fix his pump. It cycled on for a few seconds and got up to about 20 lbs pressure, and then backed off when the pump cut off. He had tried a new pressure switch with no success at fixing the problem. When I got there, it would run for a few seconds and cut off. The odd thing is that the pressure switch never deactivated to kill the power, probably due to the fact that it was not at the max pressure. So I was confused why it was not running when it had power. We ended up pulling the pump, which is 96 feet down in a well marked as 171 feet, and it's 32 feet below the water surface, based on our depth test. It had a 3/4 HP pump, one inch pipe going down.

As the pump surfaced, it was obvious the connector to the top of the pump was cracked, as water was spewing out, and the pump snapped off, just as I pulled it away from the casing. He decided to get a new pump since it had been in service for about 16 years. He got a 1/2 HP pump, as that was all in stock, and it was rated for 100 feet and we were at 96. We got new fittings, splice kit, and a double throw power switch to the pump, since I had determined that it was constantly in the "on" position regardless of on or off position.

We put it back in place, and it was doing basically the same thing with the new pump. It once got up to 50 lbs of pressure and the pressure switch kicked off one time. It never kicked off power again, but the pump would come on for about 4 secs, and after about a minute or so, it would cycle again for 4 secs and cut off, and the pressure was only about 20 lbs. The power never dropped to the pump. At the well head, it was sending 240 volts to the pump, but it will only run for 4 secs and stop. Turning the spigot on at the well head would only run water as long as the pump ran (4 secs), then stopped, so it's not a pressure backup problem.

We figured it must be a chaffed wire arching or shorting (which we talked about checking, but didn't do it). We pulled it again with some help from stronger, younger men, and replaced the wire, just because. Put it all back and same issue.

I'm now thinking this is a current issue even though it reads 119-120 volts on each leg. I'm going back to check current while it's running to try and further diagnose. I'm thinking some sort of thermal or current self-protection in the pump is shutting it off.

other info: This has a 165 gallon tank on it with recommended pressure of 38 lbs, it was at about 20 lbs, I raised it to 38, and after an hour or so, it dropped back down to about 30 lbs, and the next morning he checked it, and it was at about 80 lbs and the water gauge was maxed out. This is an odd one.

Any suggestions???
 

Valveman

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I think you are right about the 120V to each leg being the problem, as that is not enough. You can still read 115V on both legs to ground and not have 240V between the two hot wires. That will make it trip the overload in the motor in a few seconds, and then you have to wait a minute or so for them to cool down and reset before the motor will try again.

The pump has to be off and the tank empty of water before you can check the air charge in the tank. 25-28 PSI air would be correct for a 30/50 pressure switch, 38 PSI would be too much. But I don't know how it could have gotten to 80 PSI overnight if the pump wasn't even running?
 

BAPOER

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Thanks for the reply.

The pump would run only for 4 sec each time. I believe he indicated it later started running for about 15 secs before cutting off again. I suppose the accumulated cycles got it up to the higher level. However that does pose the question of why the pressure on the line pegged out when the pressure switch should have disengaged the power to the pump. I'm going over this morning to do an amperage check on it.
 

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Here's the update. I could hear a clicking sound in the electrical panel when the pump was running...and yes, it's right next to the pressure tank. I changed it out with another unused , breaker, thinking there may be a problem with the breaker. It made no difference, but it was no longer clicking. We then ran an electrical line from the pressure switch, straight to the well head and connected it to the pump... same thing. We then went from the breaker to the pump, bypassing everything else...same thing.

We completely drained the system and reset the pressure tank to 28 lbs, although it indicated to set it at 38 lbs (and it was a 120 Gal tank with 65 gal drawdown??)

We then connected the old pump directly to the breaker, and it ran fine for 15-20 seconds before I turned it off, to prevent damaging it, since it was not pumping water. We then hooked it up to the pressure switch, and it ran the same amount of time with no issues. We took it to the well head, and using the original underground wiring, connected it and it ran just fine for about 20-30 secs, before I shut it off.

Next I put an inductive amperage meter on the new pump using the original wiring, and it was pulling 55.5 amps on both legs for the 4 sec interval that it would run. I then connected the old pump and it was pulling 17 amps on each conductor. It also sounded like it might have some bearing or armature wear, as it was not running as smooth as it should.

I must then conclude, that we purchased a bad motor and pump, even though it is new. I realize the old pump is probably pulling more amps than it should, but it is 15 or 16 years old and it had mud on the outside when we removed it, so it probably has some wear, which I suppose could account for it pulling more amps than expected, and also could be the reason it was shutting down.

We will pull the pump out again and test it out of the water to see how it behaves. In the meantime another pump will be picked up to replace this one, once it's out of the casing.

Don't you just love rework...especially when it's this much of a pain?
 
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BAPOER

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Here's the final result.

It turns out we had purchased a 115V pump and not a 230V. Neither of us was aware that a 115V pump was available. Once it was wired properly on a singe pole breaker, it worked fine. I just hope we did not damage the motor during the diagnostic period. Fortunately he turned the power off while no one was at home and overnight, so that reduced the number of times the pump started up.

I expect the old pump simply failed due to age and use, and the high amperage draw is what was causing it to shutdown.
 

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