Submersible Bore Pump keeps breaking!!!

I have a 3 phase Grundfos submersible pump 42 metres to water located at front of property, house block at the back is about 3.5 metre higher than ground level where the bore is located.

Pump is located in good clean sandy soil, plenty of water on the Perth coastal plain.

PROBLEM: for the second time in about 8 or 9 years the pump has failed I think it is the same as last time about 4 years ago, will know for sure when I get it up.

Last time the shaft in the pump had snapped, suspect it has happened again, electrician has checked electricals we get power to top of bore and the motor isn't going to ground so doesn't appear to be electrical.

Grundfos couldn't give me any plausible explanation of why it would happen last time.

My neighbors bores have all been down about the same time, all used cheaper brand pumps, varying brands with no problems.

Has anyone heard of this happening with either Grundfos or any other submersible bore pump and can you offer any advice:???

Thanks in advance, I appreciate your input.

As a former driller/pump guy I reckon I can help you out.
a) Once the water leaves the bore,where does it go,how far and under what pressure?
b)Do you have a water hammer problem?
c)Is it a pressure unit with a pressure switch and pressure tank,if so what size tank?
d)What does the pump do at the top of the bore,ie.gall/hr@???psi or go metric if you want to.
e)Do you have earthed power lines near by?Is the bore steel or PVC cased.
f)Pump any sand?
More questions will come to me after you give me some input.My Grunny at my old house has been down 19yrs now.Still going.But they have had problems in some areas in the past.
Cheers,Steve.

G'day Steve...thanks for the reply


(a) Once the water leaves the bore,where does it go,how far and under what pressure?

Once it leaves the pump it is 42 metres to GL in 40mm black poly then into 50mm PVC main with 25mm to Solonoids, OA length of 50mm main is approx 50 metres mad up of approx 16 metres across the block balance up the side of house to back yard which will raise the head by approx 3.5 metres.

(b)Do you have a water hammer problem?

No water hammer that I'm aware of, I'm a plumber with 50 years experience so know what water hammer sounds like in water pipes, but I suspect it sounds different in a PVC retic system.

(c) Is it a pressure unit with a pressure switch and pressure tank,if so what size tank?

No pressure unit, no pressure switch and no tank just purely for garden reticulation.

(d)What does the pump do at the top of the bore,ie.gall/hr@???psi or go metric if you want to.

Not sure of LPM at top of bore but average is 6 x 15' Rainbird pop-ups per station with no trouble, one station has a 9 x 12' Rainbird pop-ups each station would average about 90 LPM I think, can't recall pressure at top of Bore a pressure switch is fitted but of course with no pump I can't check.


(e)Do you have earthed power lines near by?Is the bore steel or PVC cased.

(e) Nearest earthed power line is at the meter box approx 10 metres away, there is a under ground power to the meter box line is approx 8 metres away, casing is PVC.

(f)Pump any sand?

(f) No sand being pumped, sprinklers all have filters, only get cleaned if I think flow might need checking, but any sand is from replacing the odd broken sprinkler etc when some clown drives over them.

Cheers...Bill

All sounds pretty good.The three main reasons a subby shaft/coupling can fail are corrosion,cycling and a faulty checkvalve.If the pump shaft is only 304ss then it will be attacked by the motor which will be 316ss.I have seen plenty of that.If the pump cycles it will put stresses on the coupling,pump shaft and motor.The last occurs when the pump stops,water flows back down the hole past the faulty checkvalve and causes the pump to spin backwards.If the pump starts while this is happening the stress on the coupling is considerable.
In some areas around here where grunnys have failed,I have replaced them with daveys with sucess.I think the brass bit between pump and motor acts like a sacrificial anode thereby protecting both.

Quote:

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Originally Posted by Steve Fryar

All sounds pretty good.The three main reasons a subby shaft/coupling can fail are (1) corrosion, (2) cycling and a (3) faulty checkvalve.If the pump shaft is only 304ss then it will be attacked by the motor which will be 316ss.I have seen plenty of that.If the pump cycles it will put stresses on the coupling,pump shaft and motor.The last occurs when the pump stops,water flows back down the hole past the faulty checkvalve and causes the pump to spin backwards.If the pump starts while this is happening the stress on the coupling is considerable.
In some areas around here where grunnys have failed,I have replaced them with daveys with sucess.I think the brass bit between pump and motor acts like a sacrificial anode thereby protecting both.

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Steve....Thanks for the reply, BOLD numbers added to your post above are my edit to separate my questions below.

(1) Corrosion: In your opinion could this be caused by;

(a) Difference in 304ss to 316ss?

(b) Water quality?

(c) Relative distance to earthed main supply?

(d) Steel casing?

(2) Cycling:

(a) What can cause this to happen?

(3) Faulty check valve:

(a) Can this be avoided with an auxillary check valve fitted above the pump when first installed?

Also

Water hammer: How would I detect water hammer in reticulation? In my mind it would be dull thud felt/heard with the hand holding the dischrge pipe at the top of bore, when it starts.

Cheers

Bill

Hi Bill.Corrosion happens when you have a nice medium containing dissolved salts which aid the transfer of electrons between two dissimilar metals.All bore water has dissolved salts.Best water I've drilled is 180 mg/l,practically rainwater,but rainwater tanks still rust.316 is a higher grade of stainless steel than 304.If your pump element is 304 it will corrode not your motor.Plus the motor generates heat which speeds it up a bit.Is your pump shrouded?It helps.As for grounding,I have worked on a jet pump once that was leaking to earth.I kept getting little shocks,then I noticed a ring of sparks on top of the steel bore casing.That was a better earth than me otherwise..POW.Stray currents travel through the ground to find the best earth,bore water.They travel thru the steel to reach it.Your pump is literally sitting in charged water.I've seen a pump completely eaten out in 3 months because of this.And don't think your immuned because of PVC.Strays can travel outside the casing,not just thru it.Check your grounding.Is there too much leakage to earth?
Cycling happens when the pump goes on,off,on,off etc quickly.Usually a pressure switch not set right or no air in the pressure tank.I'm assuming you have manual start,so forget about this.A faulty check valve on the pump can cause this too.
Lastly,yes,I have installed a backup checkvalve above the pump but rarely.
Hope this helps.
Cheers,steve.

Sorry forgot about the hammer.You're right.When the pump stops,with your hand on the discharge,you shouln't feel to much at all.I've seen the borecap lift in exteme cases.A checkvalve fitted at the top stops this.

Quote:

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Originally Posted by Steve Fryar

Sorry forgot about the hammer.You're right.When the pump stops,with your hand on the discharge,you shouln't feel to much at all.I've seen the borecap lift in exteme cases.A checkvalve fitted at the top stops this.

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Steve

When you say "A checkvalve fitted at the top stops this." do you mean immediately above the pump or at the top of the bore i.e. ground level, when we repaired it Grundfos asked what pressure we had at top and advised I put a pressure gauge followed by a gate valve at the top and gave me an operating pressure to choke the discharge i.e. after the bend on top of the casing is the gauge and then the gate valve, can't recall what pressure they advised.

You also asked about motor being shrouded, not sure what you mean by this but it is just a standard Grundfos, can't recall model, but certainly when it was originally put down nothing was added, when we pulled it up to do the first repair it went down the same.

Bill

Quote:

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Originally Posted by bille

You also asked about motor being shrouded, not sure what you mean by this but it is just a standard Grundfos, can't recall model, but certainly when it was originally put down nothing was added, when we pulled it up to do the first repair it went down the same.

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Shrouding is usually a SS hood over the pump stages so that if the water level in the bore is too low then the water that is sucked up by the puimp runs over the pump stages and keeps them cool.....if they don't stay cool then they fail.

Parents have had a Grundfos pump down 105m for the last 12 years into hard-ish water.....no significant dramas. Setup at the top of casing is as you've been advised - check valve, pressure dial, gate valve....gate valve is choked to maintain delivery pressure.

Sorry to correct you Deadly but a pump shroud is made of PVC and is used to make the pump suck water passed the motor therebye keeping it cool.
To stop hammer install the checkvalve as near as possible to the borecap,right after the bend.And as for putting an artificial head(choking the flow)...why?Grundfos pump designations give a big hint to the optimum performance.For a subby,say an SP5A-17,this means it works best at 5 cubic metres of water per hour and it has 18 stages in the pump.I'm guessing, but is this your pump or a 5A-25?

Quote:

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Originally Posted by Steve Fryar

Sorry to correct you Deadly but a pump shroud is made of PVC and is used to make the pump suck water passed the motor therebye keeping it cool.
To stop hammer install the checkvalve as near as possible to the borecap,right after the bend.And as for putting an artificial head(choking the flow)...why?Grundfos pump designations give a big hint to the optimum performance.For a subby,say an SP5A-17,this means it works best at 5 cubic metres of water per hour and it has 18 stages in the pump.I'm guessing, but is this your pump or a 5A-25?

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OK that pretty well explains it, thanks Deadly and Steve for your input.

I've just been out to Grundfos and ran through the setup with them which they say appears to be OK.

They are checking on the incidence of broken shafts (Which is what I suspect) in a couple of other states SA and Vic I understand, and will come back to me with the answers.

In the last 2 years in Perth they say there have only been 2 x instances (Broken shafts) that Grundfos are aware of.

Bill

Grundfos are pretty good in admitting a fault.That's why I stuck so many of them down bores I drilled.You'll be right with them.

Quote:

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Originally Posted by Steve Fryar

Grundfos are pretty good in admitting a fault.That's why I stuck so many of them down bores I drilled.You'll be right with them.

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Well they haven't admitted anything at this stage but I have a bit more knowledge and confirmation that the installation is correct but the fact there has been 2 failures apparently the same (To be confirmed when we get the pump up) to the same pump has still not been resolved.

Will come back when I know some more, in the mean time I'm obviously open to, and welcome any more input from anyone.

Quote:

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Originally Posted by bille

Well they haven't admitted anything at this stage but I have a bit more knowledge and confirmation that the installation is correct but the fact there has been 2 failures apparently the same (To be confirmed when we get the pump up) to the same pump has still not been resolved.

Will come back when I know some more, in the mean time I'm obviously open to, and welcome any more input from anyone.

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Had the pump pulled yesterday, it is a 4" 5a 17 3 phase 1.5 kw, took it out to Grundfos today (Tuesday), to strip and they confirmed the shaft had snapped right at the point where the splined socket is that connects the shaft out of the motor, clean break almost appears to be metal fatiuge, same place as last time, no other signs of damage i.e. up thrust from lack of head, if anything there is very slight wear pattern (Shiny uneven marks) on the fixed bearings on the impellars which indicates to me that there is a slight down pressure..

There must be some reason behind these 2 x Failures.

The service guy had a couple of theories each doesn't really stand up so he is going email photographs to Adelaide for another opinion, should find out tomorrow (Wednesday) what the outcome is, I'll keep you posted.

UPDATE: The service manager who has only been with Grundfos for 2 years asked other branch service managers for an opinion of the cause of shafts breaking but no real opinions what the cause were offered.

I have one of my own though, in the manufacturing of the shaft the splined socket is not part of the shaft at manufacture and is not welded or screwed to the shaft but is "Friction welded" (His term not mine) by spinning the shaft at high speed an "Jamming" (His term not mine) the slightly tapered splined socket onto the shaft.

Now this must put tremendous stress on the shaft and it appears to me this manifest itself by eventually breaking a few mm inside the tapered socket where most stress would occur.

I was told that they are starting to have the socket cast into the shaft to make it an integral part of the shaft, I wonder why???
<o></o>
Grundfos made me an offer of 50% off the RRP of the Pump $1,472.00 = $736.00 + $12.00 handling fee +$748.00 + GST = $822.00 which initially seemed fair but…<o></o>
I then asked if I purchased a larger model (Which I understand has the “New” shaft) would they still give me the $748.00 off they said OK.
<o></o>
This pump was an 8a-15, RRP is $2,103.00 less $748.00 ex-gratia allowance on failed pump = $1,367.00 + $12.00 handling fee + $1379.00 + 10% GS/Tax = Total of $1,516.90. <o></o>
<o></o>
Again initially seemed fair but I was told this at 1.20 pm I had to get a Cheque to them before 2.00 pm as it would take 2 hours to clear (Wouldn’t accept any other payment i.e. Cash, Funds Transfer etc) if I made the deadlines I could pick up pump at 4.00 pm.
<o></o>
I explained I was waiting return of my vehicle from service, I told them I might be battling to make the deadline of 2.00 pm, asked if this could be done Tuesday (3 day weekend here), no problem he said except RRP would rise by 15% on Tuesday to $2,418.45 Less $748.00 = $1,670.45 + $12.00 handling fee = $1,682.45 + 10% GS/Tax Total of $1,850.69.<o>

</o> <o></o>END RESULT: I called the contractor who hauled the old pump to the surface, and was going to give a hand installing the new one on the Saturday to tell him not to bother because I hadn’t been able to pick up the pump.
<o></o>
I told him of the deal Grundfos offered, he said I was being ripped off and told me where I could buy the pump over the counter including 10% GS/Tax. For a Total of $1,316.00 with electric cable shrink kit thrown in.<o></o>
<o></o>
Grundfos acted like they were doing me a Great deal…..Yeah right!!!!:((


Moral: Don't trust pump manufacturers doing favours or great deals.