House water tank connundrum .

[edz]

A fellow worker has Two water tanks 10 m apart and  a 2 m height difference .. The water pump [ Davey impeller type ]  is level with the center of the lower tank ..
Problem is the pump will only empty the lower tank into the upper tank till the water in the lower tank gets level with the pump ..
It should have no troubles lifting the water up a  2 m  rise  over 10 m,  its not losing prime / no leaks / no check valve / 25 mm pipe from memory   .
Anyone have any ideas as to why its not able to lift the bottom half of the water capacity from the lower tank ? .

[Patr80l]

Pump can't suck or pull the water, only push it.   Water only flows into the pump by gravity.  Can you lower the pump?

[IanS]

I beg to disagree, a lot of pumps are self priming and can lift water. Have a look on the pump and see if it has a lift rating, a check valve would help to get it started but once pumping it should keep going, if it doesn't I think that you have a leak somewhere and it's sucking air in.

[krisandkev]

Can you find out the model and look at the specs and see if it mentions the lift capacity? Some pump types do not lift. When you buy a pump you generally check to see if it has a lift or draw function and how much it is, example need to draw 5 metres. This pump you mention may only be capable of gravity feed?
Fire fighter type pumps for example are specifically designed to provide a greater lift/draw as in most applications they need to suck (lift/draw) out of a dam. Also most house pumps do have a lift because many tanks are now days partly buried. Like I said, most but not all.  Not an expert just passing on a little knowledge which I hope may assist.    Kevin

[rags]

Edz, Funny you should post about a pump problem as I have just come in after installing a fire pump on the river to wet the weeds and even I sometimes have trouble and I have 25 plus years of plumbing experience doing pump installs on rural/ outer urban properties.
Sounds like the pump is cavitating when at the mention water level ( tank pressure)is equalised and so not pump anything but air bubbles.
In my experience you need 2 non return valves installed
1 at the base of lower tank as a foot valve
2 another. on the outlet of the pump ( you can get away without this one if it is an open end pipe at upper tank but if that pipe is under pressure then NRV)
Unless you haven a jet pump or a foot valve you will end up with cavitation with out the above.

Also is the discharge end into the upper tank pipe end free flowing or under pressure?

Also my suggestion is always have the pump closest to water source preferably as a flooded suction with NRV but if it needs to lift and suck then I would try and located on top of tank and use a jet pump like this
http://irrigationdirect.com.au/product/self-priming-domestic-jet-pump/

Now back down to the river to sort my problem ( pump cavitation a bit and resulting lack of flow, time to fit a NRV on suction hose but I'm not paying Bunnings for one)

[GeoffA]

I beg to disagree, a lot of pumps are self priming and can lift water.....

Not this one, apparently...

[krisandkev]

Edz, Funny you should post about a pump problem as I have just come in after installing a fire pump on the river to wet the weeds and even I sometimes have trouble and I have 25 plus years of plumbing experience doing pump installs on rural/ outer urban properties.
Sounds like the pump is cavitating when at the mention water level ( tank pressure)is equalised and so not pump anything but air bubbles.
In my experience you need 2 non return valves installed
1 at the base of lower tank as a foot valve
2 another. on the outlet of the pump ( you can get away without this one if it is an open end pipe at upper tank but if that pipe is under pressure then NRV)
Unless you haven a jet pump or a foot valve you will end up with cavitation with out the above.

Also is the discharge end into the upper tank pipe end free flowing or under pressure?

Also my suggestion is always have the pump closest to water source preferably as a flooded suction with NRV but if it needs to lift and suck then I would try and located on top of tank and use a jet pump like this
http://irrigationdirect.com.au/product/self-priming-domestic-jet-pump/

Now back down to the river to sort my problem ( pump cavitation a bit and resulting lack of flow, time to fit a NRV on suction hose but I'm not paying Bunnings for one)

My fire fighter pump can be tricky.  The Honda starts perfectly but sometimes the check valve works, sometimes not.  The foot valve is useless, I think it worked for a while when new? I have cleaned it but still no good and I do not want to buy another. I have dismantled the pump and found lots of corrosion being about 18 years old I suppose that was expected. I had a spare pump so cleaned that one inside and it pumps brilliantly but that valve!  I now just have a container of water at the pump and if there is no water in the line/pump I put a few litres in and bingo, pumps up nice and quick.  We have a large dam so our yard and gardens are nice and green; have not had rain for a while now. Just put a few sprinklers in the horse’s paddock to help the grass/feed there.  The walk down to the pump is also good exercise I guess  .  Kevin

[Troopy_03]

I don't know why his setup isn't working, but I can't see why it shouldn't work with an impeller pump. Our spearpoint pump is an impeller type, and it sucks water from the water table, about 8M down, and pushes it up 2.5M with no problem. The only valve we have is a non return valve sitting about 300mm below the pump, and all it does is allows the pump to prime. Whether the pipe below the pump still has water in it, I can't say for sure, but I'd guess it does, otherwise once the 300mm has pumped through there would be air in the pump again and cause cavitation.

[Jeepers Creepers]

Take the dead rat out of the tank.

[edz]

Thanks all, I'll have to get my mate to find the specs etc for his pump, then we can work out what it should be able to do / not do .

[#jonesy]

Given it is a friends tank and not yours maybe they don't fully understand their own system. So A few other questions (that probably don't apply).
Has it always been like this? If not what has changed?
Is the pump drawing from the bottom of the tank and not half way up.
When it gets to half way does it just keep running with no water coming out?
Does the upper tank have a return pipe/overflow to the lower tank and the water is just going round in circles.

[Frawls]

You have a NPSH problem on your pump inlet, solution if possible move  the pump to the base of the first tank. Even better locate the pump below the level of the first tank, this will provide a positive pressure on the pump inlet always a good thing.  Next check you have enough discharge head  (pressure) to pump to the top of the second tank should be ok, need pump spec to confirm.

Just for your info a Impeller type centrifugal pump works by accelerating fluid by means of a rotating motion, most pumps can lift fluid into eye of the impeller although a number factors need to be checked for this to work successfully. A positive pressure on the inlet is always preferred Vs suction lift.

Hope this helps.

[edz]

I'm thinking he will have to move the pump to the base of the lower tank and use the weight of the water in the tank to feed the pump .

[prodigyrf]

There's a bit of physics in these things and you can work it out yourself or take the problem to a specialist pump supply shop and they can usually set you straight without doing all the homework-
http://www.pumpfundamentals.com/tutorial3.htm

Having the pump gravity fed from the bottom tank would be an obvious place to start to see if it resolves the issue but that may present a major hurdle by itself (why wasn't it located like that in the first place?)

[GBC]

Start with the simple things and make sure it has suction rated hose. Might just be sucking flat. Those domestic setups are sometimes a bit average.