Electric Water Pump

[PETERTHEEATER]

I have the usual electric water pump (shallow well pump) which sucks water from a sub-level storage tank and delivers it to the house plumbing system.

I am aware that the motors on these pumps are fitted with a thermal cut-out switch so, that in the event of the motor overheating, the switch will open and prevent the motor from running. When the temperature cools sufficiently, the thermal switch re-sets allowing the motor to run.

Recently, the pump has been shutting down after a routine demand such as flushing a toilet and will not run. After 10 to 20 minutes the pump comes back on again. The pump is 4 years old and I have a similar pump in another house which is 18 years old and still running without a problem.

I have checked the electrical supply is good and good connections but cannot understand what is causing this fault.

Any ideas?

[Artisi]

First thought is something lodged in the pump case / impeller causing to run at higher load than it should - overload and hence shutdown on over temp.

[Crossy]

Is the pump actually getting hot?? See ^^^ or could be a tight bearing.

If not suspect a faulty overload switch (it'll be buried somewhere in the bowels of the motor, time for the pro's).

[PETERTHEEATER]

Is the pump actually getting hot?? See ^^^ or could be a tight bearing.

If not suspect a faulty overload switch (it'll be buried somewhere in the bowels of the motor, time for the pro's).

No, if I check it when it's in one of its wont run periods the motor is warm but not hot.

A typical example is if a toilet is flushed at (say) 2am the initial demend on the pump seems to cause it to 'not run' even though it has been unused for hours. That said, due to small leaks which are always in the system (toilet cisterns ball cocks etc) the pump will run for a few seconds 3 or 4 times an hour to top up lost pressure.

Maybe it's something to do with the pressure switch.

Edited July 8, 2009 by PETERTHEEATER

[Artisi]

A rhetorical question, how about at other times, if it doesn't run after the toilet flushes why does it run to a couple of times an hour to top up any leaks.

Maybe the pressure switch not sensing a full drop in pressure initially - ie the switch is "sticky" and interferring with the start / pressure function.

[PETERTHEEATER]

A rhetorical question, how about at other times, if it doesn't run after the toilet flushes why does it run to a couple of times an hour to top up any leaks.

Maybe the pressure switch not sensing a full drop in pressure initially - ie the switch is "sticky" and interferring with the start / pressure function.

Ah! That's the question. Like 15 minutes ago I went to take my evening shower turned on the washbasin tap to check that there was water and it ran for a few seconds then the supply petered out. No water then for 15 minutes then I checked again and the supply was there!. Sometimes it will run on demand through the day yet 'stop' in the evening or through the night.. It is a complete 'no run' as if power to the pump has been switched off. It's not like the supply tank is empty when the pump will run (cavitating) until it overheats and cuts out.

I am wondering if there is a blockage or foreign object in the strainer which sometimes backpressures as if a tap has been turned on then immediately off causing the pump pressure switch to sense the demand has shut off.

I have the same model pump feeding my garden water supply but it is in an awkward location otherwise I would swap them over.

What I need is a breakdown of a Mitsubishi pump showing the location of the strainer. Can anyone help?

[BigSnake]

Overheating, time for a new pump

[lopburi3]

You probably have a leaking foot valve in your underground tank. Replace as is cheap and see what happens.

[Artisi]

Overheating, time for a new pump

That really sounds like a good solution, especially if a new pressure switch, footvalve or NRV in the pump is all that is required to rectify the problem.

[Artisi]

I would check the footvalve (if there is needed and fitted), check the pressure switch - remove it from the tank and check that it is not blocked or the tank fitting is not blocked, check the valves internal of the pump itself. It sounds like a simple problem - just a matter of working thru all the possibilities.

[PETERTHEEATER]

You probably have a leaking foot valve in your underground tank. Replace as is cheap and see what happens.

Lopburi,

By 'footvalve', are you referring to a non-return valve in the suction line which might be located at the bottom of the line (pipe) inside the sub-level water storage tank or are you referring to a valve on/in the pump?

[jackr]

First off, check you have a decent mains connection... perhaps arcing there in the socket or under the cover.

If it's not overheating, yet knocking itself off, it's almost certainly electrical pointing to a dodgy connection or pressure switch/bimetallic thermal switch. If it were me, I'd hardwire briefly (bypassing switches) to determine if the motor runs ok. Obviously, open a tap, make sure the tank isn't empty and don't leave it in this state

[mdechgan]

Same thing happened to me.

I found out that it was a faulty capacitor. The motor didn't have enough power to run sufficiently and smoothly so when the motor was starting or running, it would sometimes hang or get stuck intermittently which causes the motor to overheat.

So I had to wait like 10 minutes before the motor would cool down again.

I took the pump and motor apart and replaced it with a new capacitor for like 80 baht from Amorn.

It running smooth now.

However your case mmight be different, like worn bearings or rust in the pump vane that causes the motor to run heavy.

[PETERTHEEATER]

Thanks for your inputs posters; time for a summary:

The pump is a standard Mitsubishi shallow well electric water pump just over 4 years old. I have experience of similar pumps in other houses in Thailand wjich have run 18 years and 10 years respectively without problem so I know the basic design is reliable and long living.

The pump is located under the house out of the elements and is well ventilated.

The storage tank is sub-level 8000 liters capacity and full.

The maximum suction head is less than 2 metres.

The maximum delivery head including shower heads is 2.5 metres.

The electrical supply to the pump is confirmed good.

A tap is turned ON and water runs normally. The tap is turned OFF. Five minutes later a tap is turned ON and no water except residual pressure. The pump will not run.

Between 10 and 20 minutes later a tap is turned ON and water runs normally, the pump runs. It might run on demand for several ON/OFF tap demands but eventually no water until later.

I spent most of this morning checking the pump. I removed the castellated plug on the inlet side of the pump and checked that the spring and valve rubber are serviceable.

When the pump does run (with no demand) after the 'wont run' period it runs for over 5 minutes before shutting off (pressure switch). Considering it should only be pressurising an already full line this is a long time and might indicate that the pump tank is empty due to a faulty NRV in the suction line allowing water to run back into the supply tank. That is the pump is losing its 'prime'.

However, I am also interested in the comment about the Condenser on the motor possibly being faulty and causing the motor to overheat.

So,I shall see if I can get a replacement Condenser/Capacitor and try that first then look at the 'footvalve' which I assume to be an NRV in the suction line, probably inside the supply tank. Since the supply tank is full, I would need to let the level run down before I go swimming!

Any further clues will be welcome.

[PETERTHEEATER]

Same thing happened to me.

I found out that it was a faulty capacitor. The motor didn't have enough power to run sufficiently and smoothly so when the motor was starting or running, it would sometimes hang or get stuck intermittently which causes the motor to overheat.

So I had to wait like 10 minutes before the motor would cool down again.

I took the pump and motor apart and replaced it with a new capacitor for like 80 baht from Amorn.

It running smooth now.

However your case mmight be different, like worn bearings or rust in the pump vane that causes the motor to run heavy.

Thanks for that. Some details please. Directly on top of the motor on my pump is a large Capacitor with a single bolt through a clamp arond the Capacitor body. This, I believe, is the motor 'run' Capacitor or are you talking of an internal capacitor which would require soldering in?

[PETERTHEEATER]

A rhetorical question, how about at other times, if it doesn't run after the toilet flushes why does it run to a couple of times an hour to top up any leaks.

Maybe the pressure switch not sensing a full drop in pressure initially - ie the switch is "sticky" and interferring with the start / pressure function.

Artesi, going back and re-reading posters comments, I need to consider your opinion that it could be pressure switch related. Yet I am sure that somehow it is the power supply to the motor that is being interrupted. But I will keep it in mind.

I have a second pump (same model and age) separately running my garden taps. If neccessary i sahll swap the motor Capacitor from that one and see if it makes any difference.

[mdechgan]

Thanks for that. Some details please. Directly on top of the motor on my pump is a large Capacitor with a single bolt through a clamp arond the Capacitor body. This, I believe, is the motor 'run' Capacitor or are you talking of an internal capacitor which would require soldering in?

There is no internal capacitor on these types of motors.

The single capacitor acts as a run and start capacitor since it is a single phase motor.

Capacitors on these pumps are externally mounted.

The cap value should be about 7.5 to 8 microfarads for a 150W motor.

I think mitsubishi really undersize their capacitors.

The motor isn't servicable. You can only replace the small bearings. However I don't think the motor is faulty, with the thermal protection chances are really low that the motor is burned out.

I don't remember how the mitsu pump was wired, if you can take a picture. I don't remember if there was 1 or 2 capacitors.

[lopburi3]

You should not have to go swimming - there should be a pipe attached by thread at top of tank which can be removed in one piece and at the bottom of that pipe a foot valve. Change the valve and replace the pipe - should only take a few minutes. Hopefully it is set up that way.

[PETERTHEEATER]

Thanks for that. Some details please. Directly on top of the motor on my pump is a large Capacitor with a single bolt through a clamp arond the Capacitor body. This, I believe, is the motor 'run' Capacitor or are you talking of an internal capacitor which would require soldering in?

There is no internal capacitor on these types of motors.

The single capacitor acts as a run and start capacitor since it is a single phase motor.

Capacitors on these pumps are externally mounted.

The cap value should be about 7.5 to 8 microfarads for a 150W motor.

I think mitsubishi really undersize their capacitors.

The motor isn't servicable. You can only replace the small bearings. However I don't think the motor is faulty, with the thermal protection chances are really low that the motor is burned out.

I don't remember how the mitsu pump was wired, if you can take a picture. I don't remember if there was 1 or 2 capacitors.

Thanks for that.

The motor runs fine when it does run. The single Capacitor is externally mounted on top of the motor by a simple clamp. It is aluminium cylinder about 40mm diameter. Two wires from the Capacitor run into a 'lashed up' cable bundle which the expert pineapple farmer electrician has bound together with black PVC insulating tape. I have just investigated that bundle by splitting it apart in case there are any bad connection. All but two connections are crimped and cap insulated. The two that are not are to the Pressure Switch directly connected to the top of the pump tank. I have remade them mechanically.

The Capacitor is marked as 40 Mf. When I reconnected the pump it started immediately and ran sweetly before stopping (overheat I expect) so we got some water. Tomorrow I will remove the Capacitor from my other (garden water) pump which is the same model and age and try it on the house pump to eliminate components.

[Crossy]

Have you tried bypassing the pressure-switch just to eliminate the beastie from your enquiries

[PETERTHEEATER]

You should not have to go swimming - there should be a pipe attached by thread at top of tank which can be removed in one piece and at the bottom of that pipe a foot valve. Change the valve and replace the pipe - should only take a few minutes. Hopefully it is set up that way.

Thanks Lopburi, it took me several reads of your advice before I quite understood it.

You are saying that the vertical rigid pipe (suction line) should be connected by a screwthread near the top so I should be able to inscrew it in one piece and lift it out of the tank to replace the check valve (footvalve) at the lower end.

I shall look in the morning but I am not confident that it is threaded; more likely cemented Thai bluepipe.

[PETERTHEEATER]

Have you tried bypassing the pressure-switch just to eliminate the beastie from your enquiries

Crossy, there is a Pressure Switch attached directly to the top of the pump base tank and electrically connected into the wring harness.

If I isolate it electrically I'm not sure that the motor will even run but I will keep it in my mind as I work through the options; thanks.

There is also a diaphragm gizmo (or is it a pressure regulator) attached to the top of the pump base tank which has a small daimeter hose terminating under the spring-loaded valve on the pump inlet.

I don't quite understand how the pump works so it complicates the troubleshooting.

Edited July 9, 2009 by PETERTHEEATER

[Crossy]

Have you tried bypassing the pressure-switch just to eliminate the beastie from your enquiries

Crossy, there is a Pressure Switch attached directly to the top of the pump base tank and electrically connected into the wring harness.

If I isolate it electrically I'm not sure that the motor will even run but I will keep it in my mind as I work through the options; thanks.

There is also a diaphragm gizmo (or is it a pressure regulator) attached to the top of the pump base tank which has a small daimeter hose terminating under the spring-loaded valve on the pump inlet.

I don't quite understand how the pump works so it complicates the troubleshooting.

The switch should just be a simple on-off device (two wires). Turns on when the pressure decreases.

If you short the wires the pump should run (you can use a regular light switch for safety) try on and off a few times (with a tap on so you don't build too much pressure), if the pump starts every time suspect the pressure switch.

PLEASE be careful

The diaphragm gizmo is likely an automatic air bleed, to ensure there is sufficient air in the pressure tank (they don't work properly if full of water).

[mdechgan]

Thanks for that.

The motor runs fine when it does run. The single Capacitor is externally mounted on top of the motor by a simple clamp. It is aluminium cylinder about 40mm diameter. Two wires from the Capacitor run into a 'lashed up' cable bundle which the expert pineapple farmer electrician has bound together with black PVC insulating tape. I have just investigated that bundle by splitting it apart in case there are any bad connection. All but two connections are crimped and cap insulated. The two that are not are to the Pressure Switch directly connected to the top of the pump tank. I have remade them mechanically.

The Capacitor is marked as 40 Mf. When I reconnected the pump it started immediately and ran sweetly before stopping (overheat I expect) so we got some water. Tomorrow I will remove the Capacitor from my other (garden water) pump which is the same model and age and try it on the house pump to eliminate components.

40 MF? Are you sure?

How many watts is your motor and pump?

[PETERTHEEATER]

FIXED!! - But let me explain what it was for future troubleshooters.

Early this morning I removed the motor Capacitor and fitted the known servicable Capacitor from my garden pump which is the same make and model.

The pump motor was hot so I switched it off and left it to cool for 30 minutes. I then switched on and the pump ran smoothly and supplied water for almost 20 minutes before overheating and shutting down again.

Not the Capacitor then.

I then got inside the sub-level storage tank which is a couple of metres deep and found that the suction pipe is PVC Blue cemented and that the strainer and footvalve are at the bottom. I didn't fancy a scuba dive but with the aid of a strong torch checked that the strainer was clear.

By chance, a Thai friend dropped in and I put it to him. He inspected the pump with power OFF but with a tap open and showed me a teardrop (literally) of water oozing from the rim of the impeller cover. I removed the impeller cover (4 bolts). The impeller housing and cover are bronze. There is an annular groove around the inside rim of the cover in which sits an 'O' ring seal. There was a witness mark (cupro green) on the inside of the rim which indicated a pin hole leak.

What happens is that when the motor runs and the impeller spins it draws in air through the pin hole. The amount of air trapped in the impeller housing slowly increases (mixed with water) until the pump cavitates compressing the air until the pump and then the motor overheat causing the thermal cut-out to operate.

The fix was straightforward. I polished the annular groove with very fine sandpaper to remove any roughness and degreased it with Toyota brake cleaner (excellent for many household jobs!) The 'O' ring was serviceable so I cleaned it with the solvent then applied a fine film of petroleum jelly. It was then re-assembled and tested.

Now, the pump starts when a tap is turned ON and stops within a second when the tap is tuned OFF. Before, it would continue to run for anything up to 5 minutes.

So, a new pump at 11,600 baht avoided. Next time that I am out shopping I will pick up a 50 baht 'O' ring and replace it at next failure.

Thanks for your inputs posters, most were valid.

Incidentally, one thing that was overlooked by me and not suggested by anyone was to check that air can get into the storage tank. Liken it to a car. If air cannot get into the fuel tank (inward vent valve) the engine will eventually starve of fuel. My tank is concrete with a firm fitting concrete slab cover. Over a period of time the gap between the cover and tank wall can become blocked preventing air from getting in as the water level falls which might cause overload of the pump and motor as it tries to pull a vacuum! Unlikely? Don't bet on it; just check!

[Artisi]

Pleased to see that the problem has been solved - as I said in an earlier post - probably something simple - just a matter of finding it.

Just one point to make the terminology 100% correct.

Air leaking into the pump until such times as the pump losses prime IS NOT cavitation, the correct term is airlocked or airbound.

Cavitation results when the inlet of the pumped liquor (water) is at a lower pressure than what is required by the impeller to maintain cavitation free operation. Cavitation is one of the least understood and missed used phenomenon / terms in the pump business.

If anybody wants the low-down on cavitation I can post something by way of explanation.

[Crossy]

Definately one for the file, I hope you bought your friend a suitably large bottle

With a surface tank the tiny hole wouldn't be an issue and a good point about tank ventilation.

[PETERTHEEATER]

Pleased to see that the problem has been solved - as I said in an earlier post - probably something simple - just a matter of finding it.

Just one point to make the terminology 100% correct.

Air leaking into the pump until such times as the pump losses prime IS NOT cavitation, the correct term is airlocked or airbound.

Cavitation results when the inlet of the pumped liquor (water) is at a lower pressure than what is required by the impeller to maintain cavitation free operation. Cavitation is one of the least understood and missed used phenomenon / terms in the pump business.

If anybody wants the low-down on cavitation I can post something by way of explanation.

You are correct and I used the wrong terminolgy. It needs air to cause an airlock or airbound condition but cavitation does not.

I shall amend my last post to relect that. Thanks.

[Artisi]

Pleased to see that the problem has been solved - as I said in an earlier post - probably something simple - just a matter of finding it.

Just one point to make the terminology 100% correct.

Air leaking into the pump until such times as the pump losses prime IS NOT cavitation, the correct term is airlocked or airbound.

Cavitation results when the inlet of the pumped liquor (water) is at a lower pressure than what is required by the impeller to maintain cavitation free operation. Cavitation is one of the least understood and missed used phenomenon / terms in the pump business.

If anybody wants the low-down on cavitation I can post something by way of explanation.

You are correct and I used the wrong terminolgy. It needs air to cause an airlock or airbound condition but cavitation does not.

I shall amend my last post to relect that. Thanks.

After 40 years in the pump business I was probably being pedantic - but it is nice to get everyone on the same page with terminolgy plus it was an opportunity to correct a common misunderstanding, especially for anyone who was interested.

You comment regarding having the tank vented is a very valid and an important point otherwise you would have real cavitation .

Edited July 11, 2009 by Artisi

[PETERTHEEATER]

There is a sequel to this. By chance, my neighbour started having the same problem with his pump; overheating and shutting down. (A Hitachi)

I helped him through the same troubleshooting procedure I had followed but everything checked out. I was squatting next to the pump - which had now gone cold but still would not run - trying to think logically and tapped each item idly with the handle of my screwdriver as I mentally ticked it off. As I clicked the Pressure Switch (PS) the motor started.

By switching on and off and tapping the switch now and then it became evident that the switch contacts were 'sticking' internally. Here's the scenario:

Tap ON, pump runs, tap OFF pump stops. Good

Tap ON pump runs, tap OFF pump motor continues to run and run and run trying to pump water into the system on which there is no demand. Inlet water and water in pump gets warm then hot motor is loaded and gets warmer then hot at which point the Thermal Cutout operates to protect the motor. Sometimes, as the pump cooled the PS would 'click' as the contacts switched to the correct position other times not.

The Pressure Switch is mounted directly on top of the pump tank from which it senses pressure. After removing the cylindrical plastic cover from the PS an adjusting screw is found underneath. Making tiny adjustments on this it was possible to get the pump to work reliably albeit with a slight reduction in flow and pressure output.

A new pressure switch has been sourced but I shall be examing the dodgey one.

The PS is mounted to the top of the tank on a hexagonal (nut type) connector. Should the pump tank be drained before removing the old one? Any tips?