Pump Question

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augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
Someone refresh my memory.
I have a friend that has a submersible pump he uses for irrigation.
The pump has begun tripping the overload and in "troubleshooting" by long distance I am trying eliminate possible electrical problems and cover the mechanical issues. I can not recall the conditions that would cause an overload such as input or output restrictions or lack thereof. What "plumbing" situation would cause the overload ?
 
i have noticed around here that most of the submersible wells used to have a 90 amp overload breaker for a 15 hp single phase well,just built 2 services for new wells last week and they both had a 100 amp overload,usually by the time im called out for the problem you have described ,the well man has already bypassed the overload and the pump motor will be tripping the main breaker by then which is usually a 125amp.if the capacitors are all good and the relay is good then that dont leave much to do but pull the pump motor and repair or replace,usually replace.also if the well starts pumping sand will cause the amp draw to go up also.
 
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pumps are sized for

1. amount of volume they are intended to pump.

2. amount of elevation they need to lift the water.

restricting the amount of volume being pumped will reduce current in the motor - it is performing less work.

Pressure should not make much difference for a centrifugal type of pump.

Pressure will make a difference on a positive displacement type of pump.

All submersible pumps I have seen are centrifugal with multiple stages, higher HP usually has more stages.
 
Jim W in Tampa said:
Too high of head pessure will do it. Has anything changed recently like pressure switch or number and size of lines.
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To add to what Jim said if the pump is older and any thing electrical has been ruled out I would guess the bearing are starting to wear out between the motor and pump causing more load on motor.
 
I would start with testing the capacitors if it has an above ground controller. Also if the start relay has failed, it will also cause the overload(s) to trip. Usually though its a bad cap.
 
small single phase, nameplate amps 9.6. Was tripping overload after 5 to 10 min., now in less than 2 min.
I have not seen the install, but was trying to tell hum what possible mechanical problems to check prior to having to investigate the electrical (it's 100 miles away)
 
Many of these will have a run cap also, but these are items that can be checked with a OHM meter to some extent by reversing the meter leads and watching for the reading to fall off, an analogue meter works best for this, the only other thing is to check the ungrounded conductor with a high reading OHM meter to ground, any leakage could mean bad insulation on wiring or motor, also you can un hook the motor at the top of the well head by removing the cap, and taking the conductors apart, this will show you which it is, other then what the others have said, theres not much to these pumps.
 
Dennis Alwon said:
15 HP single phase pump?????? Do you mean 15 amp?
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no i assumed he was talking about a large irrigation well like we have around here for rice irrigation,and the largest single phase wells we have around here are 15 hp 240 volt,and they have a single pole 100 amp breaker in the control box that one of the hot legs run through for motor protection
 
Jim W in Tampa said:
Too high of head pessure will do it. Has anything changed recently like pressure switch or number and size of lines.
Click to expand...

Your wrong about to high a head pressure. I worked for a water utillity for 33 yrs. We would throttle the discharge valve to lower the pump current. More flow equals more current. More head less current. High head only causes pump cavitation.
 
One-eyed Jack said:
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Low head will cause cavitation.:D
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Closing off the discharge valve to much for a high head can cause the water to boil in the bowls of a deep well turbine pump. Thus loss of water lube, bearing and cavatation damage results. With the correct suction, a Lower head creates a higher flow. But if the cone of depression falls below the screen you can also cause a pump to break suction. The start of dry pump condition ( as perhaps what you mean by low head cavitation). One of the reasons why we would back off on the flow using the discharge valve. I have seen this happen to submersibles as well when the current would drop out. But anyway I don't want this to become a big blow out here. Just giving out what I experienced from my many years in the water field.
 
technoid52 said:
Closing off the discharge valve to much for a high head can cause the water to boil in the bowls of a deep well turbine pump. Thus loss of water lube, bearing and cavatation damage results. With the correct suction, a Lower head creates a higher flow. But if the cone of depression falls below the screen you can also cause a pump to break suction. The start of dry pump condition ( as perhaps what you mean by low head cavitation). One of the reasons why we would back off on the flow using the discharge valve. I have seen this happen to submersibles as well when the current would drop out. But anyway I don't want this to become a big blow out here. Just giving out what I experienced from my many years in the water field.
Click to expand...

Yes if you shut the flow off completely you will boil the water and get cavitation. If you have flow at high head you won't boil the water. If you overpump the well you will get a slug of air and I agree it is bad news for the pump. In your instance a low head could cause overpumping and an air slug. What I was referring to was a low discharge head on a "JET" pump. This can cause a low pressure environment at the impeller inlet and cause a bubble of air. Same deal, cavitation and bad news for pump/impeller.
 
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