Oil well motor

[storeytime]

I am troubleshooting a problem with an oil well pump motor. It is 240V, 1PH, 5HP, 20.2 FLA.

I was called because it kept tripping the heaters. I set them at 25.25A - 20.2 x 1.25= 25.25

On an amperage check under load the amperage was pulling 5-6 amps on the down stroke of the well pump. It was fluctuating up to about 34-37 amps on the pump (up) stroke for about a half second. I was told that the pump would run for about an hour and a half before it tripped the overload heaters.

I'm not real familiar with oilfield mechanics, but I could only come up with these conclusions:
1 - Something mechanical on the pump was making the motor work too hard on the pump action. (Oilfield people set the counter weights on the pump at lightest setting - still tripped)
2 - The motor was not big enough for this well. (Several other wells in this field use this exact setup with no problem)
3 - Something in the well itself was putting it in a bind, maybe blockage or bent casing. (just guessing, again I don't know anything about drilling & pumping. The landowner came by and told me that they had bent the first pipe and had been having a lot of trouble cleaning this one out)
4 - The motor is bad. (I ohmed the motor leads out and they ohmed out good, no short to ground)

Does anybody have any other possiblilites on this or a better way to see what is happening in this situation? I'm going tomorrow to run the pump and do amperage checks for a longer period of time than I did the first time.

 

[Joethemechanic]

What exactly did they do with the counterweights? It sounds like you need more counterweight or counterweights acting on a longer arm, not less. There is usually a a lot of weight in the wire rope and and column of oil to be counterbalanced.

If you are saying they removed or lessened the mechanical advantage of the weights, then they went the wrong way.

 

[storeytime]

I assumed he lightened it because he said you could turn the pump with your hand, which meant to me that he had lessened the amount of counterweight.

 

[Joethemechanic]

The counterweights are on the crankshaft, right?

Or are there some on the walking beam?


And when you are saying upstroke, you do mean with the wire rope being pulled up the well casing don't you?

 

[storeytime]

I wasn't there when the operator told me what he did involving the counterweight, but from looking at the pump, I assumed he meant on the beam behind the head. In other words, on the opposite side from the wire rope.

Yes, upstroke is referring to the wire rope being pulled up the casing.

 

[Joethemechanic]

Sounds like you either need more weight, or you need to move the weight on the walking beam away from the fulcrum (away from the cable) It's like a fat kid and a skinny kid playing on the see-saw. The skinny kid had to move out to the end, or the fat kid had to move towards the center. I think right now, your cable end is the fat kid.

That damn thing should just about be ballanced so that the only work your motor is doing is lifting oil

 

[Joethemechanic]

It's been a long time but I am thinking the procedure to properly balance is, with a full column of oil, you should be able to disconnect the johnson rod (connecting rod) and the counterweight should drift downward pulling the cable up the well casing. That is when the weight is correct. And I mean it should pretty much drift, no slamming or banging. But the column has to be full to the top of the discharge piping.

Id that thing isn't set up right, it will not only overload the motor, it will also overstress the gearbox, gearbox mounting, and johnson rods

Preferably when you balance, you should disconnect the johnsons from the crankshaft end.


You got a picture of this thing?

 

[storeytime]

Thanks a lot Joe. That helps me have a whole lot better understanding before I go back out there tomorrow. I'll have all of this on my phone where I can communicate a little better with the operator. It makes sense to me that it's not balanced right.