How high (no, not an oriental joke!) can you lift water?

[Chris Holmes]

Theoretical question.

My father in law recently read a thriller and part of the plot was some Russian ganster types attempting to refuel a plane by using a surface mounted pump to bring the fuel up 100 or 200 feel (from a WWII vintage storage tank).

He reconned this was nonsense, as you cant go over about 30 feet as you can't maintain a vacum above that.

This I am sure was true back in his National Service day.

Is it still the case? or has modern technology re-written the laws of physics?

If not, how could you (ahem) get it up?

Would you need intermediate storage tanks every 30 feet or so and a series of pumps?

Or is it just that "ye cannae change the laws of physics" and it can't be done?

Curious Chris

[The Natural Philosopher]

The answer is yes and no. Ultimately what do you mean by a surface mounted pump?

There are forms of pump that have the motor at the top but use a variety of tricks to produce pressure at the bottom of a well for example..

But you cant SUCK petrol up very far, you have to BLOW it up :-)

[Davey]

Agreed. The standard type of water well pump has a pump at the very bottom of the pipe, and the electric supply goes down to the pump, so that the pump only has to push. Being immersed, it is self-priming. If that type is not possible, then the only way I see of doing what is suggested is to seal the tank, and then pressurise it, to force the fuel upwards.

[John Rumm]

You can't suck it more than 30' since that is how high atmospheric pressure will push it if you stick a vacuum in the pipe above it. However you can push it to any height you like within reason. So if the pipe is at the bottom, it can do 200' in one operation.

[Nightjar]

Is this a novel where the hero also ends up beating a flame front up a ventilation shaft after blowing the fuel up? If so, the idea of sucking the fuel up using a pump mounted at the surface is not the only technical error in the book.

Lifting by suction pump works by air pressure on the surface of the liquid pushing it up a pipe that has been evacuated by the pump. Petrol is less dense than water so, with a perfect vacuum, the maximum it could be lifted would be about 45 feet. In practice, the pump would not achieve a perfect vacuum, so 35-40 feet is a more probable limit. To raise it more than that, you need a force pump - one that creates enough pressure at the base of the pipe to lift the liquid against gravity. It would be possible to use repeated short lifts into reservoirs, but, although that was the way deep mines were once drained due to the limitations of the equipment, it would not be necessary in this case. Raising petrol a couple of hundred feet with a force pump would only need a fairly modest pressure of about 4.5 bar

Colin Bignell

[Andy Dingley]

It's not unusual to suck fluids up more than 30' though - just pressurise the tank too. Where metering of a substance is required, it's not unusual to pressurise the tank to avoid the suction lift limit, but still to use what's basically a suction pump for delivery, because this makes metering its volume easier.

Also it's about 28' suction limit for water, but rather higher for lighter petroleum. However a useful limit is much less that that, because you want to avoid cavitation in the pump and so pumps almost never work right down to zero absolute pressure.

[Chris Holmes]

You forgot - using only his hands/arms! 1:=)) Yes, that's the one.

Facinating discovering how common or garden pumps worked. I'm sure my Physics teacher must have explained this somewhere along the line, but I just didn't get school at the time 1:=(( Actually, I don't think he did. I think he was a good teacher, maybe the school/system he was in (early days of large state comps) was a limiting factor.

C

[Chris Holmes]

Would force pumps have been around back in the late 40s / early 50s or are they a modern invention?

[GB]

They were used in mines from the early days of steam.

[Dave Plowman (News)]

If the pump was on the surface of the tank you can go to pretty well any height using a force pump. Basic schoolboy physics. If the pump were in the aircraft, different matter.

[Clive George]

Force pumps are pretty simple in concept - an example is a bike pump.

The slightly harder bit is sealing the pipework etc against the pressure, but that's not that hard.

[charles]

and only 30" for mercury!

[Lobster]

A Jack Reacher perchance?

David

[Chris Holmes]

been claimed by my learned colleague Mr Bignell

[Tim Streater]

Presumably the plane was flying round in circles? And also presumably the truck would have had to do the same.

[Alan Braggins]

[...]

The plane is parked on the ground. The storage tank is 200' below ground. There is no truck.

[The Natural Philosopher]

There are a couple of other ways I have seen...pumping part of what you get up, down, and using a sort of venturi effect to get up more than you pump down. The motor and primary pump stays at the top but the business end is still at the bottom.

[GB]

Out of interest, did they have a hand pump or an electric one?

A very, very small plane has a fuel capacity of 200-300 litres. A jet of some sort, probably 20 to 200 times that. So, they might be raising something between 200 kilos and 40 tonnes a distance of 200 feet vertically, using a pump that is probably only 50% efficient.

That would take quite some time by hand. I bet that it was done in 10 minutes in the story?

[Lawrence]

Could you allow water to enter the pipe so that the fuel would float to the top? Just a thought.

[Harry Bloomfield]

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