Pump Destroying Casing Rust

Greetings to all,

Do any of you technicians, plumbers, well drillers or repair personnell have thoughts or methods that you might share that might be less cumbersome or less costly than what I am contemplating below?

I have inspected the ground up impellers of my prior two 4" submersable pumps, and found 1/8" magnetic granules in both the interiior and exterior cavities.
The first of 3 similiar pumps was installed on 4 Sept 1987 and removed 11 Mar 1994.
The present pump is exibiting the exact same symptoms as the prior two.
I installed this third pump on 22 Oct 2007.
The pump down on each new throttled pump is significant only in that the water level drops about 10 to 11", and recovers in about 40 seconds at 25gpm. All pumps were 1-1/2 HP S.S. submersable, with max efficiency while pumping at 25 gpm.

The immediately prior pump had been suspended at 80', while the current one is at 60' in the 110' deep well.
The riser pipe is 1-1/2" schedule 80 PVC. The carbon steel casing is 6" X1/4" wall of unknown length.
The well does not have a tag or tracable record, and is possibly 40 years old or older, and is sunk at a very slight angle off of true vertical.

Because of the slight tilt and the 4" pump resting against the side of the 6" casing, much rust dropping from above is pulled into the close spaced pump intake as witnessed constantly by my filters and rust packed irrigation sprinklers.
During the installation of the last pump I made an attempt to use 3 standard 6" pump centering spacers. This proved a waste of $ and 50 minutes of our time, as the pitless adapter would not allow anything beyond the dimension of the pump to pass betweeen it and the opposite wall of the casing..

Our next attempt at correction to this problem will involve the assistance of a well repairman.
I will dig down to the level of the pitless adapter in order to temporarily remove it. We expect to use 5" schedule 80 PVC as a liner from the bottom of the casing, with a packer or shale trap affixed to the bottom of the PVC sleve and extending a short distance above the present well head. The annulus area will then be filled with bentonite chips to a distance just below the existing pitless adapter hole.

The sleve will at this time be forced against the hole where the adapter is to be reinstalled, to insure no interference during reconnection.

After the bentonite has solidified the PVC sleve must be internally cut off below the pitless adapter hole and the adapter will at this time be reinstalled in the casing.

SiuncerelyOlder Handyman

I don't think you will ever get 5" PVC inside 6" steel casing. Especially if there is any rust. Even if you can, there won't be any annulus left to seal. It seems like a lot of trouble and expense that may not fix the problem. It may not cost much more to have a new hole drilled to put that 5" PVC casing into.

I don't see what good the 5" is going to do in the first place.

I know you said the rust from the pipe was getting into your pump, but I think you will find that most of that rust is from your water. The pump laying against the casing could cause a little vibration to be heard somewhere, but beyond that, I can't see where it could be a problem.

I agree with both comments.

I've never had a problem getting cable guards or a torque arrestor down past a dovetail type pitless adapter. You do have to push harder or rotate the pipe a bit but that's it.

If you want the motor away from the casing, rig a 1/2" spacer or two on the motor or install a tail piece on the motor that will cause the water to be sucked up from under and past the motor to get into the inlet screening.

Have you had a water test done for iron?

Also, how long do you think a throttled back 25 gpm pump should last? And what do you mean by throttled back? And how much water are you pumping; hours on end irrigating etc.?