Tapping water from well by gravity -- calculations

[chrblhjj]

[Mentor Note: Thread moved from the schoolwork forums to the technical forums, since it appears to be a real-world problem]

If I have a water well 55m deep
I want to suck water by gravity without any pump.
I put a barrel of 85 liters and connect it firmly to a pipe of 55m length going into the well.
The pipe is 1.7 cm diameter.

I closed well the barrel to create vacuum inside of it so the water comes up.
It didn’t work.

The parameters I thought of changing are:
• the length of the pipe
• the width of the pipe
• the size of the barrel

But how to calculate these?
What are the formulas in question to know what are the limits within which the system will work?

Thanks in advance for everyone who can help.

Relevant Equations: Water density
Atmosphere pressure

No idea

 

[BvU]

Homework Statement: If I have a water well 55m deep
I want to suck water by gravity without any pump.
I put a barrel of 85 liters and connect it firmly ti a pipe of 55m length going into the well.
The pipe is 1.7 diameter.
I closed well the barrel to create vacuum in the barrel so the water comes up.
It didn’t work.
The parameters I thought of changing are:
• the length of the pipe
• the width of the pipe
• the size of the barrel
But how to calculate these?
What are the formulas in question to know what are the limits within which the system will work?
Thanks in advance for everyone who can help.
Relevant Equations: Water density
Atmosphere pressure

No idea

A long time ago, Toricelli already discovered that you can't suck up water for more more than ten meter.

Your scenario does not reveal what energy source you want to use instead of a pump ?

$\$

 

[chrblhjj]

My scenario consists of using negative pressure.
First step is filling the barrel by a the big amount of water (85 liters).
The barrel has two connections:
• one in the top for the pipe going down to the well.
• another one at the bottom to let the water out of the barrel to a water tank.

Second step is opening the bottom faucet of the barrel: the water starts to go out of the barrel. Negative pressure will be created inside the barrel because it’s closed firmly. The only way to compensate is to suck from the upper pipe that is going down to the well. First, it should suck the air, and second the water.

I’m relying on the big difference in the weight of the water in the barrel (85 liters) versus the amount of water in the pipe (20 liters approximately).

In one of my trials, the barrel collapsed. I had to make a steel structure to support the barrel from inside.
Now it’s not collapsing, but the water isn’t going up either.

 

[BvU]

difference in the weight of the water in the barrel (85 liters) versus the amount of water in the pipe (20 liters approximately)

Another law of physics is about communicating vessels. It's not the weight (mass) that is important, but the pressure. And the pressure follows from the height of the liquid, not the width.

So:

The only way to compensate is to suck from the upper pipe

If the barrel is 1 m high, it can suck (siphon) 1 m of water, no more.


Bringing up 1 kg of water from 55 m below requires 550 Joules of energy. You have to provide that one way or another.

$\$

 

[FactChecker]

My scenario consists of using negative pressure.
First step is filling the barrel by a the big amount of water (85 liters).
The barrel has two connections:
• one in the top for the pipe going down to the well.
• another one at the bottom to let the water out of the barrel to a water tank.

Second step is opening the bottom faucet: the water starts to go out. Negative pressure will be created in the barrel because it’s closed firmly. The only way to compensate is to suck from the upper pipe that is going down to the well first the air and second the water.

So you are trying to suck the water up 55 meters. That is way too high. As @BvU said, the limit is 10 meters. after that, the water column gets too heavy and a vacuum will form in the suction tube.

I’m relying on the big difference in the weight of the water in the barrel (85 liters) versus the amount of water in the pipe (20 liters approximately).

That ratio doesn't matter. You could have a thousand liters in a barrel and it would not work. Only the air pressure at the bottom of the well really pushes the water column up. Once that column gets too heavy for the air pressure to push it higher (at 10 meters), a vacuum forms in the pipe. There are shallow and deep "jet-pumps" that will work from above ground to get water up 6 and 49 meters, respectively. A well deeper than that requires a submersible pump near the bottom of the well.

 

[Baluncore]

@chrblhjj
You might drop a submersible pump down the well, then drive the pump with a water-powered hydraulic motor.

When you push a small volume of high pressure water down to the motor, it drives the lift pump, before it exhausts into the well. The pump lifts a greater volume of water, up and out of the well.

You will need a pump at the surface to drive the small volume of water down the well. The drive water pipe can be inside the water lift pipe, That reduces the hydraulic pressure difference

Now all you must do is find the source of energy to drive the high pressure pump at the surface.

 

[berkeman]

Now it’s not collapsing, but the water isn’t going up either.

https://www.alamy.com/stock-photo/well-bucket-winch.html?sortBy=relevant

 

[Averagesupernova]

Her is a clue:
-
Forgive me for not using metric units the entire way through this.
One cubic inch of water weighs .036126842 lbs. Atmospheric pressure at around 15 psi means we can lift water into a vacuum 415.2 inches using atmospheric pressure since a column of water an inch in cross section area would weigh about 15 lbs. Do the conversion (2.54 cm per inch) and the height of the column of water cannot be more than about 10 meters. There just is not enough atmosphere to push it any higher.

 

[FactChecker]

The height limit for drawing water out of the well is 10 meters. That includes any form of siphoning. All solutions will have to involve either pushing the water up from your 55 meters or using several stages of drawing water up in steps of less than 10 meters. If you can specify the requirements and limitations more completely, then maybe someone can help.

 

[Baluncore]

If I have a water well 55m deep

What will the water be used for ?
What minimum flow volume do you require from the well per hour ?

You must have energy to lift water from the well.
Where will that energy come from?

 

[Flyboy]

As others have pointed out, there’s no way to siphon/suction from that deep. You need to push the water up from the bottom.

Given the nature of the initial question, I am interpreting this as a situation where economical electrical power to drive a modern well pump is either unreliable or unavailable. Would that be a correct assessment?

If so… windmill pumps are still very much a practical option. They still make new units, and the spare parts to maintain them.

 

[Lnewqban]

If I have a water well 55m deep
I want to suck water by gravity without any pump.

Welcome, @chrblhjj !

That is not possible.

Please, see:
http://www.clean-water-for-laymen.com/deep-well-hand-pumps.html

 

[FactChecker]

As a matter of curiosity, is there some way to use suction is smaller steps (say 8 or 9 meters in each step) to get water up to the top?

 

[Flyboy]

Maybe? But that requires, in this case, at least 6, probably 7, pumps working at essentially maximum power to be possible. As it is you will run into issues with cavitation on hot days or days with low barometric pressure, and if you’re not close to sea level you’ll need even more pumps.

A single pressure pump at the bottom pushing water up is honestly the most efficient, reliable, and practical solution, which we’ve known for, what, 150+ years?

 

[chrblhjj]

What will the water be used for ?
What minimum flow volume do you require from the well per hour ?

You must have energy to lift water from the well.
Where will that energy come from?

The water will be used for household.
I need like 100 liters per hour. (Approximate daily consumption being 2400 liters).

I thought the difference of energy would come from the difference of weight between the water inside the pipe and the water inside the barrel. But it shows there are other factors like the atmosphere pressure play a role too.

 

[chrblhjj]

As others have pointed out, there’s no way to siphon/suction from that deep. You need to push the water up from the bottom.

Given the nature of the initial question, I am interpreting this as a situation where economical electrical power to drive a modern well pump is either unreliable or unavailable. Would that be a correct assessment?

If so… windmill pumps are still very much a practical option. They still make new units, and the spare parts to maintain them.

The application of such a system would definitely be essential where economical electrical power to drive a modern well pump is either unreliable or unavailable. But it's not my case.
I have 24/7 electricity and a fair enough solar system and lithium batteries. I also have a submersible pump that works more than fine.
It's just a matter of curiosity and a better understanding of how things work in life. I saw a video of people taping water from a nearby depth. I thought I can do it on bigger scale.

 

[chrblhjj]

As a matter of curiosity, is there some way to use suction is smaller steps (say 8 or 9 meters in each step) to get water up to the top?

I don't think so, because the well diameter all the way down is like 40 cm, and the water head in the well is at around 15m deep.

So apparently no way to suck more than 10.5 meters, and no way also to make many steps since no access to an intermediate point below the opening of the well.

 

[Tom.G]

I never measured the water level in the well, so this may be totally wrong.

It may be possible to pump water from a 40ft. (12m) well. I grew up with drinking water from a 40ft. well, with the pump at ground level in the utility room.

I believe it was a "jet pump", with the pump sending pressurized water down a pipe, then using entrainment to bring additional water back up a second pipe.

Ahh! Google to the rescue:
https://support.boshart.com/what-components-are-used-in-a-shallow-and-deep-well-jet-pump-system

Cheers,
Tom

 

[FactChecker]

I have 24/7 electricity and a fair enough solar system and lithium batteries. I also have a submersible pump that works more than fine.
It's just a matter of curiosity and a better understanding of how things work in life. I saw a video of people taping water from a nearby depth. I thought I can do it on bigger scale.

Good! Then you have the best solution for a well that deep (55 meters). As far as satisfying your intellectual curiosity, the situation is that it is too deep for anything else. A submersible pump can work for wells much deeper. A deep-well jet-pump could work down to 49 meters. A shallow-well jet-pump could work down to 7 meters. Both of those require electricity. Suction from the top will only work down to 10 meters but 6 meters is about the practical limit. The fast-moving jet of water in a jet-pump essentially helps more water come up the pipe (see this).

 

[DaveC426913]

In one of my trials, the barrel collapsed. I had to make a steel structure to support the barrel from inside.

You have made a pressure vessel the size of a barrel. If it's 20"h x 18"d that's about 4,775 sq in. With a hard vacuum, that would be about 65,000 pounds of pressure, about as much as 26 cars.

When it implodes it can do so with enough force to injure or kill you. Supporting it inside simply means you will get a higher vacuum before it implodes, possibly sending steel shrapnel everywhere.

You are messing with forces beyond your ken.

I have reported this as a dangerous activity.

Hopefully you will take the advice of others here and go with safer and more practical methods.

 

[Baluncore]

I have 24/7 electricity and a fair enough solar system and lithium batteries. I also have a submersible pump that works more than fine.

Use that for now.
Monitor the level of the water in the bore. The level will fall depending on how quickly you draw water from the well. The level may also vary according to the seasons. Record that data as it will help manage the well.

What is the temperature of the water in the well, or as it is drawn from the well ?

 

[DaveC426913]

The water will be used for household.
I need like 100 liters per hour. (Approximate daily consumption being 2400 liters).

Is this a lot for a well? It sounds like a lot.

 

[FactChecker]

Is this a lot for a well? It sounds like a lot.

It is small. Mortgage companies want to see recovery rates of 2 gal/min or more from a well. 100liters/hr = 0.43 gal/min. A small family can do ok with that but needs to conserve reasonably and a cistern is often required. Private wells often have recovery rates of 10 to 100 gal/min (38 to 380 lpm = 2280 to 22,800 liters per hour)

 

[phinds]

I don't get how the numbers in the last couple of posts make any sense.

 

[Averagesupernova]

If a well can't supply 100 liters an hour it's next thing to dry in my opinion. That's only 26 gallons an hour.

 

[FactChecker]

I don't get how the numbers in the last couple of posts make any sense.

View attachment 350354

Are you talking about the unit conversions (maybe mistakes were made) or about the comparison with your reference? There are large variations in water usage. One hint is where the link says that 70% of use is indoors. To me, that means it is dominated by apartment dwellers who do not water lawns, plant crops, have animals, or fill swimming pools. Private wells in the country are quite different.

I know people (4 adults) who just moved onto a farm (no crops) where the well produces (recovery rate) about 460 gallons per day and there is a large cistern. They also have 5 goats and 4 dogs. They are conscientiously trying to conserve water. They still have to bring in tanks of water regularly.

 

[jack action]

I don't get how the numbers in the last couple of posts make any sense.

View attachment 350354

Assuming a pump combined with a well with a recovery rate of at least 2 gal/min:
$$\frac{300 \frac{gal}{day}}{2\frac{gal}{min}} = 150 \frac{min}{day} \equiv 2.5 \frac{h}{day}$$
So the pump would be required to work at most 2.5 h/day to get 300 gal/day. I'm not sure what doesn't make sense about all these numbers.

 

[Tom.G]

Don't forget about average vs peak water use.

i.e. Watering lawn, Taking shower, Running dishwasher, Washing car
All at the Same Time!

Cheers,
Tom

 

[Baluncore]

The well flow rate will depend on the geology, and the recharge rate.

My regional water well drilling companies, charge at two different rates per metre, depending on the final flow rate. You tell the drilling company where to drill, and when to stop. If sustained flow is less than 5000 litres per hour, the well is classed as a dry hole, and so costs less. I know of several wells that end below sea level, and have virtually zero flow, so you can still lose.

There is also the possibility that the water will have a very high flow rate, yet be so saline, that it is unsuitable for the irrigation of crops, so is only suitable for stock water in a desert.

The drilling company is very careful not to suggest where, nor how deep you should drill, so you cannot dispute their service contract.

The water diviners will always be right. No matter where they say you should drill, there will always be some water, or they will claim the hole deviated by a couple of metres, missing their underground river.

As an interested geologist, I offer to take bets on the quality of the water and the flow rate with depth. That is a free, yet profitable, local service I offer, that gains me more local geological and hydrological information. It can also bias where a well is drilled, without me being liable.

 

[FactChecker]

Don't forget about average vs peak water use.

i.e. Watering lawn, Taking shower, Running dishwasher, Washing car
All at the Same Time!

Yes. Even if the average gives plenty of water, it may not support the required peak rate unless water is stored in a cistern.

 

[FactChecker]

If sustained flow is less than 5000 litres per hour, the well is classed as a dry hole, and so costs less.

That sounds wrong. That is 22 gallons per minute. Are you sure it is not 5000 liters per day? That would be 0.9 gallons per day, which seems reasonable to call it dry.

 

[Baluncore]

That sounds wrong. That is 22 gallons per minute.

I use SI litres or m³, as it is too easy to confuse gal(imp) with gal(US).

The critical estimated flow was 1000 gal(imp) per hour, but is now 5000 litre/hr.
That is a small farm supply, not a house supply.
It is not worth running a well pump for less.

Farmers are economists, who use land, to convert water into money.
When it is dry, they need more water to stay afloat financially.

 

[Averagesupernova]

Farmers are economists, who use land, to convert water into money.
When it is dry, they need more water to stay afloat financially.

To put things into perspective, an inch of rain on one acre is about 27000 gallons. The size of the well used for irrigation of crops is in an entirely different league than a piddly 1000 gallon per hour well. In the USA a 1000 gallon per hour well will keep up with spraying crops but certainly not irrigation.
-
1000 gallons per hour won't meet the demands of large dairy operations either. More than one well is needed if for no other reason than backup. Even in communities with public water systems where the reliability is very good they will have a well or two.

 

[FactChecker]

I use SI litres or m³, as it is too easy to confuse gal(imp) with gal(US).

Good point. My recent experience was in terms of US gallons. I see why liters is better.

The critical estimated flow was 1000 gal(imp) per hour, but is now 5000 litre/hr.
That is a small farm supply, not a house supply.
It is not worth running a well pump for less.

Farmers are economists, who use land, to convert water into money.
When it is dry, they need more water to stay afloat financially.

You are talking about a working farm. I have only been considering a small, non-working farm that people live on with a hand-full of animals. I have no idea how much water a working farm of any size requires.

 

[Baluncore]

If sustained flow is less than 5000 litres per hour, the well is classed as a dry hole, and so costs less.

As I explained, 5000 litres per hour is classed as a dry well.