How do submersible pumps work?

[JohnW2]

It's a bit of a surprise the gap is that big, however the principle is still there. the impeller will still set up the water flow and I dare say a vortex to suck more in.

As I keep being 'forced' to say, given that it clearly works, it presumably must be essentially as you are suggesting - but that doesn't make me any less surprised, essentially to the extent of struggling to believe what clearly must be the case, particularly given the size of 'the vanes'!

Kind Regards, John

 

[ericmark]

In my early years I worked for SLD pumps, and manly Flygt Pumps, there were two main types, fresh water and sewage pumps, fresh water had an impeller and volute the latter covered in rubber and we had to trim them, burning a little rubber so very close contact, with the sewage type it was more like a snail shell, there was a brass wear ring but both cases centrifugal force pumped the water, and they had mechanical seals with a void filled with a special oil between them, needed servicing regular which included changing oil and testing seals with compressed air. The motor rotor ran in air. Even the 2" pump could be completely stripped down.

But for what we charged for a weeks hire in 1970's you can likely buy a pump now. The modern pump has many ways to stop water ingress including a potted stator and allowing water around the rotor instead of air.

The main thing that killed pumps was running dry, and even in the 70's we used sensors on top of pump and a current sensor so as water reached top of pump it started, and as soon as it started to draw air it stopped. But floats are cheap, but in the main needed more water between start and stop.

The old Flygt 2" single phase pump had all the relays and start/run capacitors in a box in the dry, 7 core cable between the two, really over engineered.

But be it a car water pump, a central heating pump, or a submersible pump they all worked in a similar way for pumping water.

 

[conny]

If that were the case, then I'd find it much easier to understand. However, the impeller vanes are actually about 50 mm above the plate containing the 'input hole' - in fact, close to the top of the output port



Kind Regards, John

That height is so it gets a good flow of water and helps to stop too much dirt being dragged up from the floor of the container it is set in, however, where I have come across this in the past there is usually an insert plate quite close to the vanes to help create the drag of the water. My own subby is similar to the one in the earlier pictures and has such a plate which also helps stop prying fingers being caught, (though in my opinion anyone who sticks their fingers into a spinning pump/motor/fan deserves to injure them).

 

[conny]

In my early years I worked for SLD pumps, and manly Flygt Pumps, there were two main types, fresh water and sewage pumps, fresh water had an impeller and volute the latter covered in rubber and we had to trim them, burning a little rubber so very close contact, with the sewage type it was more like a snail shell, there was a brass wear ring but both cases centrifugal force pumped the water, and they had mechanical seals with a void filled with a special oil between them, needed servicing regular which included changing oil and testing seals with compressed air. The motor rotor ran in air. Even the 2" pump could be completely stripped down.

But for what we charged for a weeks hire in 1970's you can likely buy a pump now. The modern pump has many ways to stop water ingress including a potted stator and allowing water around the rotor instead of air.

The main thing that killed pumps was running dry, and even in the 70's we used sensors on top of pump and a current sensor so as water reached top of pump it started, and as soon as it started to draw air it stopped. But floats are cheap, but in the main needed more water between start and stop.

The old Flygt 2" single phase pump had all the relays and start/run capacitors in a box in the dry, 7 core cable between the two, really over engineered.

But be it a car water pump, a central heating pump, or a submersible pump they all worked in a similar way for pumping water.

Good old Flyght pumps. Even the small ones weighed a bloody ton! Stripped down many of them over the years for rewind. Getting the stator out of the pot could be a nightmare if you didn't set it up right and heated the casing very quickly to allow it to drop out. Same fears when putting it back in. You had to have the core pack perfectly aligned above it while you heated the casing up. Tilt the stator slightly or don't get the casing evenly heated enough all round and it was a bitch to try and get back out once it got stuck.

 

[just pumps]

Oh the stink created by heating to remove the windings was something else, well remember three of us standing outside in the pi$$ing rain with gas torches. Can`t remember what make of pump it was but do remember a guy using a gas torch on a stuck impeller and the look on his face when being plastic not metal it started to melt!

 

[SUNRAY]

.... something like ....

View attachment 203052

Kind Regards, John

I've just had a quick look at mine, it's hard to see detail but the space between the vanes and the inlet plate looks to be 5 to 10mm.

 

[conny]

Oh the stink created by heating to remove the windings was something else, well remember three of us standing outside in the pi$$ing rain with gas torches. Can`t remember what make of pump it was but do remember a guy using a gas torch on a stuck impeller and the look on his face when being plastic not metal it started to melt!

I've seen that happen a few times. LOL

I've just had a quick look at mine, it's hard to see detail but the space between the vanes and the inlet plate looks to be 5 to 10mm.

For a domestic single phase that not bad. On industrial ones they are not much closer. On the flgyt pumps with a volute bowl they don't have that plate at all, just a few short stumpy protrusions to create a small gap between the bowl and the surface it stand on. Biggest I worked on was approximately 10', (3 metres), tall and had to be stood upright on the back of the wagon as the seal chamber was filled with coolant oil. This had to be done at the workshop even though there is/was a law against transporting equipment containing oil for fear of spillage. It was nerve wracking to be standing on a ladder propped against the pump, to check it fitted under the roller doors as the wagon pulled out of the workshop. Happy to say we had about 3" to spare.

 

[conny]

This is mine. Can pump up to 9,000litres per hour and up to 6metres which is quite impressive.
The impeller blades are tapered and at their nearest point to the base it about 5mm gap, (difficult to measure through such a small hole).
The inlet hole is 35mm diameter and the outlet is approximately 17mm bore so twice as much input as output. The force is reasonable but the volume is amazing. It can empty a hot tub in about 20-30 minutes and I used it to empty my above ground swimming pool, (18' x 12' x 4'), in about 3 hours.
Think it cost £50 from SF a few years back.

 

[SUNRAY]

This is mine. Can pump up to 9,000litres per hour and up to 6metres which is quite impressive.
The impeller blades are tapered and at their nearest point to the base it about 5mm gap, (difficult to measure through such a small hole).
The inlet hole is 35mm diameter and the outlet is approximately 17mm bore so twice as much input as output. The force is reasonable but the volume is amazing. It can empty a hot tub in about 20-30 minutes and I used it to empty my above ground swimming pool, (18' x 12' x 4'), in about 3 hours.
Think it cost £50 from SF a few years back.

View attachment 203080 View attachment 203081 View attachment 203082

I'm happy to say that's a different quality device to mine, about twice as fast and I know from pumping out a basement getting it over 4m slowed it down a fair bit. It was half the price too so a classic get what you pay for.

 

[SUNRAY]

For a domestic single phase that not bad. On industrial ones they are not much closer. On the flgyt pumps with a volute bowl they don't have that plate at all, just a few short stumpy protrusions to create a small gap between the bowl and the surface it stand on.

But don't they have a tangential cage rather than the style of impeller we've been discussing?

 

[JohnW2]

That height is so it gets a good flow of water and helps to stop too much dirt being dragged up from the floor of the container it is set in, however, where I have come across this in the past there is usually an insert plate quite close to the vanes to help create the drag of the water. My own subby is similar to the one in the earlier pictures and has such a plate which also helps stop prying fingers being caught....

I've just had a quick look at mine, it's hard to see detail but the space between the vanes and the inlet plate looks to be 5 to 10mm.

For a domestic single phase that not bad. On industrial ones they are not much closer.

This is mine. Can pump up to 9,000litres per hour and up to 6metres which is quite impressive.
The impeller blades are tapered and at their nearest point to the base it about 5mm gap, (difficult to measure through such a small hole).
The inlet hole is 35mm diameter and the outlet is approximately 17mm bore so twice as much input as output. The force is reasonable but the volume is amazing.

But don't they have a tangential cage rather than the style of impeller we've been discussing?

Right .. so experiences (and pumps!) clearly vary a lot ...

The two I dismantled yesterday were identical 400W Silverline ones, similar price and external appearance to conny's Titan one.

The impeller blades are almost exactly 50mm from the base with the 'inlet' hole in it (easy to measure with that base removed), and 5mm or so from the top of the outlet orifice. The impeller is horizontal (not tilted), so all parts are 50mm from base/inlet. It's vanes/blades (per photo I posted yesterday) are tiny (about 7mm 'wide/high') and curved, but the same width/height throughout their length, so not tapered. The inlet and outlet orifices are about 30mm and 34mm diameter respectively, and there is no 'shaping' of any sort on the inside of the chamber on the approach to the outlet orifice. The impeller, and its vanes/blades is both horizontal and totally symmetrical, so it will be trying to fling out water equally in all directions (horizontally), but only a very small proportion would 'hit' the outlet orifice (the diameter of that orifice is only about 8% of the circumference of the chamber).

I have to say that what I had expected to see was an impeller (or 'turbine') with very much larger blades/vanes than this, and
EITHER the impeller/turbine in an 'enclosure', the 'output of which was connected to the output port, with no 'continuity' with anything else (particularly not the 'inlet').
OR, if the impeller/turbine were not so enclosed, at the very least some sort of crude valve on the inlet (maybe a rubber flab or a 'ball in a cage'.

... but I'm seeing neither of those. If the design I'm seeing had been described to me, or shown to me on paper, I think I would probably have 'put money on' (and lost!) it not being able to work as an effective pump, let alone the extremely effective one that it is. My intuition therefore remains very upset, even though I cannot deny the evidence of my eyes!

Kind Regards, John

 

[Harry Bloomfield]

... but I'm seeing neither of those. If the design I'm seeing had been described to me, or shown to me on paper, I think I would probably have 'put money on' (and lost!) it not being able to work as an effective pump, let alone the extremely effective one that it is. My intuition therefore remains very upset, even though I cannot deny the evidence of my eyes!

All the impeller has to do, is produce a differential in pressure and the water will flow. The do this by 'flinging' the water out from the centre of the impeller, in the general direction of the outlet. Gaps are large, because not much actual pressure is needed for the application. For higher pressure demanding applications, tighter gaps are needed with the only way out being via the outlet.

 

[conny]

But don't they have a tangential cage rather than the style of impeller we've been discussing?

Some have an impeller very similar to a ships propeller but usually only 2 blades whereas a ship normally has at least 3 blades, but you are quite right in that some have vanes which are like the bucket scoops on a waterwheel. On the waterwheel the bucket fills with water and is then pushed around whereas on the pump drags the open end behind as it turns through the water so creates a low pressure area. This low pressure area fills with water which is expelled through centrifugal force around the volute until it exits through the outlet spout. It's a fine balancing act between the impeller being large enough to expel the maximum amount of water and proximity to the casing so as not to put the impeller, (and ultimately the motor section), under excess pressure against the water it is turning in.

 

[JohnW2]

... The force is reasonable but the volume is amazing. It can empty a hot tub in about 20-30 minutes and I used it to empty my above ground swimming pool, (18' x 12' x 4'), in about 3 hours.

Similar experience here.

Many years back (before I had a generator) I suffered the unfortunate combination of protracted very heavy rainfall and an equally protracted power cut. As a result, my (very large) cellar got entirely flooded to a depth of about 20 cm - it's roughly 120m², so that's around 24,000 litres. When power was restored, the pump (similar to what we're discussing) cleared it all in an afternoon, probably 4 hours or thereabouts (which is, of course, more than the recommended continuous running time - but that didn't seem to harm it).

Kind Regards, John

 

[JohnW2]

All the impeller has to do, is produce a differential in pressure and the water will flow. The do this by 'flinging' the water out from the centre of the impeller, in the general direction of the outlet.

Yes but, as I said, given the total symmetry of everything (other than the outlet), only about 8% of the water flung out by the impeller will be "in the general direction of the outlet".,

Gaps are large, because not much actual pressure is needed for the application. For higher pressure demanding applications, tighter gaps are needed with the only way out being via the outlet.

As I also said, it seems that (if the pump is in pretty shallow water) it manages to keep a pressure differential of about 0.7 bar (around 10 lb/square inch), which is far from insignificant, between the inlet and outlet orifices, about 50 mm apart.

This is very difficult! I obviously know that 'it works', but everything in my mind and 'intuition' tells me that it shouldn't (at least, nothing like as well as it does work), given everything I've described!

I suppose it must be a bit like currents in the sea. Relatively small and circumscribed high velocity currents can, presumably, result in quite marked pressure differentials between places very close together within what appears to be 'the big wide ocean'!

We're talking about a chamber about 14 cm diameter and about 7cm long, with two holes, 30mm and 34mm in diameter respectively, about 7cm apart. If one raised the pressure within any part of that chamber by any means other than 'flinging water about', I would not really expect any significant amount of water to come in through one of those holes and out through the other.

Kind Regards, John