[st425]

I'm looking for a battery operated water pump that can get water from a well to a cattle trough (about 140m, elevation +5m). There's 5 cattle. Can?t get my head around what I need amp/watt/bar wise. Any recommendations?

[naturelovingfarmer]

Rather than try to lift 140 meters of water, why not lift it 6 and let the gravity do the rest? If you don't need it to be really fast, you can use a simple 15 amp pump. You'd put a plastic barrel on stilts with 2 fittings. The top fitting's hose goes to the pump. The fitting on the bottom goes to a valve you can reach easily and which fits a standard agricultural hose. Then just attach 140m of hose and make sure it's watertight. The water will actually flow down, and then back up the hill from hydraulic equilibrium. It's how the Romans did aqueducts over especially wide or deep valleys, they did it down one hill and back up the other and were just careful not to have it leak. It's the principle behind water towers in the city. You need a less powerful pump to raise water straight up than over a long incline. And gravity will move it the rest of the way. With the pump going up 6m to a tank through a 25mm hose, it only has to lift 2.94 liters of water at once. It would have to lift 68.8 liters if you sent the same hose up the hill without a tank.

[Womble]

You need a less powerful pump to raise water straight up than over a long incline. And gravity will move it the rest of the way. With the pump going up 6m to a tank through a 25mm hose, it only has to lift 2.94 liters of water at once. It would have to lift 68.8 liters if you sent the same hose up the hill without a tank.

Noooo!, that's really not how it works!!

Without getting too technical, the pressure needed to raise water is the height x the density of the water x acceleration due to gravity. Because we're on earth, we can assume water pretty much always has the same density, and gravity always applies the same force. That means you can sort of ignore those two things, meaning that the pressure needed to raise the water is proportional only to the height you're trying to raise it by, and has nothing to do with the horizontal distance travelled.

It's true that going a horizontal distance as well as a vertical one will take more energy, but that's to do with frictional losses along the length of the pipe because the water is flowing, rather than the height itself. Does that make sense at all? 

[landroverroy]

You need a less powerful pump to raise water straight up than over a long incline. And gravity will move it the rest of the way. With the pump going up 6m to a tank through a 25mm hose, it only has to lift 2.94 liters of water at once. It would have to lift 68.8 liters if you sent the same hose up the hill without a tank.

Noooo!, that's really not how it works!!

Without getting too technical, the pressure needed to raise water is the height x the density of the water x acceleration due to gravity. Because we're on earth, we can assume water pretty much always has the same density, and gravity always applies the same force. That means you can sort of ignore those two things, meaning that the pressure needed to raise the water is proportional only to the height you're trying to raise it by, and has nothing to do with the horizontal distance travelled.

It's true that going a horizontal distance as well as a vertical one will take more energy, but that's to do with frictional losses along the length of the pipe because the water is flowing, rather than the height itself. Does that make sense at all? 

I understand you're an engineer Womble. So the answer is. . . ??

[naturelovingfarmer]

 

You need a less powerful pump to raise water straight up than over a long incline. And gravity will move it the rest of the way. With the pump going up 6m to a tank through a 25mm hose, it only has to lift 2.94 liters of water at once. It would have to lift 68.8 liters if you sent the same hose up the hill without a tank.

Noooo!, that's really not how it works!!

Without getting too technical, the pressure needed to raise water is the height x the density of the water x acceleration due to gravity. Because we're on earth, we can assume water pretty much always has the same density, and gravity always applies the same force. That means you can sort of ignore those two things, meaning that the pressure needed to raise the water is proportional only to the height you're trying to raise it by, and has nothing to do with the horizontal distance travelled.

It's true that going a horizontal distance as well as a vertical one will take more energy, but that's to do with frictional losses along the length of the pipe because the water is flowing, rather than the height itself. Does that make sense at all? 

Which is heavier, a 140 m length of rope or a 6 m length of rope? If you have to carry it up a hill, you'd be able to tell the difference I tend to think. Even if I don't use the right words for why it works, it does still work that way. If you make a U-shaped pipe and pour water in one end, water will come up just as high in the other. And if you fill a tube with approx 3 liters of water, and another with 68, the 68 will be more work to move around. If there isn't a clear reason why it's basically magic. But in this case I tend to think it's just gravity and mass.

[Womble]

If you make a U-shaped pipe and pour water in one end, water will come up just as high in the other.

Yes, that's right - it's how a builder's level pipe works, for instance.

And if you fill a tube with approx 3 liters of water, and another with 68, the 68 will be more work to move around.

OK, bear with me here. If I dive 5m down in a small swimming pool, the pressure my ears feels is the same as if I dive 5m down in a big swimming pool, right? Pressure = height x density x acceleration due to gravity - the amount of water present doesn't matter at all, only it's depth.

Beyond that, it's messing with my brain as to how to explain it simply, but trust me - if it wasn't like that, I'd have lost my job a long time ago. Edit: Try this - it's not the weight of the water in the hose that matters, it's the flowrate you move it at. So, ignoring frictional losses for now, moving 1 litre per second of water in a 1" diameter pipe takes exactly the same energy as moving 1 litre per second in a 10" diameter pipe. (Actually, even if you DID take account of the frictional losses, it would take less energy to move the 1 litre per second in the big pipe than the small one, even though the amount of water held up in the big pipe weighs more). I don't know if that helps, but anyway.....

I understand you're an engineer Womble. So the answer is. . . ??

Without overcomplicating it, you don't need a massive pump, because you don't need a massive flowrate. 5m of height gain is literally 5m of water head (or half a bar, if the pump is quoted that way). So I'd go with something which has a "dead-head" static pressure increase at the left hand end of the pump curve of around 10m (or 1 barg) - basically 5m plus a bit more for luck, and to overcome frictional losses. If it ended up being a bit more than that then fair enough - it will just pump at a higher flowrate.

The harder question is how to control it, since you won't want the pump running all the time, and it's hard to put a level sensor in the trough, because it's a long way away. The easiest solution for that is to do exactly what naturelovingfarmer suggests, and have a small header tank on stilts (assuming the layout will allow that - you'd be aiming for the level in the the header tank at the low part of its cycle just before the pump turns on to still be a bit higher than the water level in the trough). Then you have a submersible pump in the well, which runs on a float switch in the header tank to keep the header tank continually topped up. The outlet of the header tank then flows under gravity, as NLF says, to the trough, which would have a standard ball-cock arrangement. As long as you get all of the air out of the long pipe, that will work just fine. It will still freeze in the winter though!

HTH!

[naturelovingfarmer]

Okay, now it makes sense. Odd how different the reasoning is between the educational channel and an engineer on the internet. You'd think the history channel would do better research.

Speaking of u-shaped pipes... can you explain a ram pump? It uses momentum and weight of a large amount of falling water to lift a small amount of water high up. If the depth matters more than the weight, how does a ram pump actually work?

[Womble]

Sure! I don't want to sidetrack this thread though, so I've started another one here.

[chrismahon]

Pumping the water into a header tank is fine in theory, but at 5 metres high it won't be a simple structure. I very much doubt there is a 12v battery pump that will deliver 5 metres head over 140 metres of pipe though, so the tank may be the only option? First stage is to see what pumps are available. They usually quote performance based on an outlet pipe the same diameter as the pump outlet (I'm looking at pumps at the moment) so if you go smaller you won't achieve the published figures. You will need a float switch in the tank- usually they are attached to the pump.

[Womble]

Ah, I had hoped that some of the 5 metres would be inside the well!  The header tank could be pretty small though.


Edit: DYOR, but for instance, I think this pump would do it, Chris (either to a header tank, or all the way to the trough if you could sort the control aspect out). It can do 10 litres/minute at 1 bar differential. So, for going all the way to the trough, if 0.5 bar is used to overcome the 5m height difference, that leaves 0.5 bar for frictional losses. A very quick go on [size=78%]Pressure Drop Online-Calculator (pressure-drop.com)[/size] for 10 litres/minute of water through 140m of 1" plastic pipe gave a pressure drop of just 0.15bar, so that should be ok, right?

[st425]

Thanks all for your input!

We took a chance on this a while ago, and it does the job.

It’s not quick, but we just turn it on whenever we’re with the cattle and it works out fine.

https://www.ebay.co.uk/itm/124225838972

[chrismahon]

Pleased you found something st425. Your calculations are quite right Womble, but my real concern was the power drain on any battery system.


I ended up buying a pump as well. 4m head and through 80 metres of 15mm pipe delivers about 100 litres per minute. The power consumption is a massive 1100W. I'm going to try and improve that delivery rate by switching to 19mm pipe. The main restriction is the bore of the push-fit connectors and there are three necessary, which currently squeeze the flow down to 10mm.

[naturelovingfarmer]

I also just bought a well pump. Hand powered, because electric service is sometimes unreliable this far from town. I dug the well by hand. Dipping into it by bucket was getting to be a hassle. A spring-pole and rope would have made it easier, but I lacked a suitable tree that I was willing to fell. This pump is locally made. I don't really understand how it works, it resembles a forge fan inside except that it doesn't draw from the cheek and blow out the nose like a forge fan, it comes up from below, and is reversible so I can put unused water back in the well. Kind of nifty. It comes with an attachment for putting it on the standard screw thread that is on storage tanks. Says you can pump anything that isn't caustic.