How do submersible pumps work?

[JohnW2]

Hi, I have a drainage system in my large cellar, which includes a submersible (mains voltage) pump which pumps water up out of the sump - this sort of thing (random pic from internet) ...

I've just had to replace one because it suddenly developed an L-E fault (around 10kΩ at 500V), presumably due to water getting somewhere it shouldn't be. Even if I could discover a way of dismantling it, I doubt that it would be worthwhile attempting to 'repair it'.

However, I have a couple of others lying around which were taken out if service (one after not at all long in service) because they 'stopped pumping'. Both are electrically OK, and both make buzzing noises indicating that the motor is trying (maybe even slightly succeeding) in turning when powered up - but they don't pump. My suspicion is that something has got clogged up/jammed by debris - which, if the case, might (at least theoretically) be fairly easy to rectify (a better option than sending them to the tip!).

However, at least without attempts at dismantling, I can't for the life of me see how they are meant to work, hence where I could find places that might be clogged up. The water intake is through holes in the bottom, and the pump output is on the side, fairly near the bottom (per piccie). However, both of those seem to go into the same chamber, which makes no sense to me. If I pour water into the outlet, it immediately comes out of the 'inlet' holes in the bottom, and vice versa.

Has anyone got any idea as to how these things actually work (i.e. how/where does the 'pumping' happen) and, in particular, has anyone got any experience of dismantling one of them?

Kind Regards, John

 

[just pumps]

"Holes in the bottom" will be a grill which will be screwed on, twist on/off on or a press fit to release. Under the grill is an impeller and it is this that generates the force to pump water up and away as it err, rotates.
Might get lucky and find a twig behind the grill which is stopping the rotation.

Please ensure power is discontected when dismantling.

 

[Burnerman]

Nicely efficient, these things as being submerged there is no need to use up energy to prime.....the high speed impeller pressurises the water kinetically and gives the pump surprising delivery performance.
Mine has screws in the bottom to remove the grille...its not a trash type pump though, just dirty water.
John

 

[jj4091]

They work by the rotor & coils being sealed into the body & as you suspect you cannot service them. The impeller is driven independently by magnetism & the 2 faces get contaminated preventing rotation of the impeller so as others have said you should be able to get at the impeller & clean the faces & remove any blockage. Ours comes apart with a quarter turn of the impeller body while holding the main body firmly.

 

[just pumps]

They work by the rotor & coils being sealed into the body & as you suspect you cannot service them. The impeller is driven independently by magnetism

Some you can and some you can`t service. Some impellers are screwed on to the motor shaft others are magnetic drive, some pumps have mechanical seals whilst others have simple lip seals, all depends on how much the pump costs really.

 

[333rocky333]

We used to use them in pub cellers, as others say usually the most you can do is get the base unscrewed, they often make that buzzing when they cant move, but once the base is off you can spin the rotor to see if its free, even run it dry for a while and see whats going on, to be honest sometimes you can flick it round with a lump of wood and it starts but once stopped it then struggles to start again

 

[just pumps]

We used to use them in pub cellers, as others say usually the most you can do is get the base unscrewed, they often make that buzzing when they cant move, but once the base is off you can spin the rotor to see if its free, even run it dry for a while and see whats going on, to be honest sometimes you can flick it round with a lump of wood and it starts but once stopped it then struggles to start again

Flick to start but wont start on its own is often the capacitor.

 

[333rocky333]

Flick to start but wont start on its own is often the capacitor.

Yes, i had the Capacitor go on my lawnmower, easy fix, in the pubs we were instructed to just fit a new pump as they needed it pronto, we must of dumped loads of pumps , as you say maybe easy repairable and usefull to someone, not sure where the Caps even located on ones like Johns picture.

 

[just pumps]

Yes, i had the Capacitor go on my lawnmower, easy fix, in the pubs we were instructed to just fit a new pump as they needed it pronto, we must of dumped loads of pumps , as you say maybe easy repairable and usefull to someone, not sure where the Caps even located on ones like Johns picture.

Would be in the top black section however before people start trying to take them apart the more expensive type are oil cooled so can easily get rather messy!

 

[JohnW2]

Many thanks for all your rapid responses. Quoting just a typical one ...

We used to use them in pub cellers, as others say usually the most you can do is get the base unscrewed, they often make that buzzing when they cant move, but once the base is off you can spin the rotor to see if its free, even run it dry for a while and see whats going on, to be honest sometimes you can flick it round with a lump of wood and it starts but once stopped it then struggles to start again

OK, I've semi-dismantled one of them (the one which was not in-service for long) and, although I think this one is probably a 'lost cause', I'm still intrigued as to 'how/why it works' (when it does!).

The bottom was in two parts, so two sets of 4 screws to remove. It was totally clean inside, and the impeller could be spun easily by hand. However, on application of power, it just buzzed by didn't spin. 'Flicking it around' did, sometimes (but not always) get the motor going, but it would never start again (without flicking) after it had stopped. It therefore seems that something is wrong with the motor and/or its control, quite possibly ...

Flick to start but wont start on its own is often the capacitor.

. However, I suspect that if I attempted to address that (if I could find a way into the motor housing), I would be unlikely to be able to get it adequately water-tight again?

I'll move on shortly to the other one! However, more generally, I still don't really understand how they ever work (pumping-wise). As I said, both inlet and outlet going into the same chamber (containing the impeller). As can be seen in the pic below, the inlet 'hole in the bottom' is not much smaller than the outlet pipe (both about 1" diameter), with no valve - so why does the water come out of the outlet, at relatively high pressure, without at least equally going back out of the 'inlet' hole?

Kind Regards, John

 

[Burnerman]

When the pump starts, the centre of the impeller is at low pressure.....the swirl of the impeller causes water to be drawn in and forced around the vanes at high pressure to the outlet port.
The impeller needs to run in an enclosed space to be at its most efficient and prevent water escape.
John

 

[just pumps]

The "Vanes" on the impeller (lets call them that for now) are angled to move water in a certain way and whilst I can`t quite see from the photo on yours often the housing is not central to the impeller but is set up to be nearer the housing and just past the outlet therefore by closing the gap the water is pushed out. I spent 5yrs in pump R&D before computers were doing this stuff and by moving housings around you get a BIG difference however the wear life on bearings and and other parts have to be considered, well that and the end user of course.

A good example of this is the Mazda rotary engine where the vanes follow the shape of the housing around. Different but a good example none the less.

 

[just pumps]

When the pump starts, the centre of the impeller is at low pressure.....the swirl of the impeller causes water to be drawn in and forced around the vanes at high pressure to the outlet port.
The impeller needs to run in an enclosed space to be at its most efficient and prevent water escape.
John

Like a vortex.

 

[Burnerman]

Yep, that's the one
John

 

[Harry Bloomfield]

The 'swirl' shaped lips on the bottom of that impeller, once it begins spin, will fling the water out to the sides of the impeller through centrifugal force, then out via the discharge port. That will cause a low pressure in the middle of the impeller which draws in more water from the base.

The don't produce much water pressure, but shift a large volume.

The square box (float switch) contains a large ball bearing and a pair of contacts at the cable end of the box. If the box is raised up by increasing water level, the box floats cable end lowest, the ball drops inside the box and shorts the contacts out which causes the pump to run until the box falls again, as the water is pumped out. You can hear the ball inside rattle, if you shake the float switch.