Water column and pressure

  • Thread starter Prabhahari
  • Start date
  • #1

Main Question or Discussion Point

How to pull up the water which is 800 feet below the ground? How much amount of pressure to be applied ?

Can we use P = dgh


Reply me as early as possible?
 
Last edited:

Answers and Replies

  • #2
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,666
How to pull up water which is 800 feet below what? What are you talking about?
 
  • #3
Steam King, Its below ground ?
 
  • #4
And let me Know how much amount of pressure to be applied?
CAn we use
P = dgh + atm pressure
 
  • #5
Baluncore
Science Advisor
2019 Award
7,407
2,452
You cannot pull it. You have to put the pump down the hole, then pump the water out.
Each 30 feet of water is about one atmosphere. 800 / 30 = 26.66 atm = 387 psi.
That is about 2 foot per psi.
 
  • #6
19,914
4,092
If you install a well casing down a borehole to a depth of 800 and perforate the casing at the 800 ft depth level, water will fill the casing, and you can draw water out of the casing from the top (at close to the depth of the water table (usually within a couple of 10's of feet from the surface) using a pump. The water within the casing at the top will be replaced by water from 800 ft below, until all the water within the casing is from the 800 ft. depth.
 
  • #7
Baluncore
Science Advisor
2019 Award
7,407
2,452
Chestermiller said:
water will fill the casing,
That is wishful thinking. You are very lucky to be living in an area where, when you dig a hole, it fills up with water. My water table is at 90m. I am only 100m ASL, but 10km inland.

Poorly fractured rocks have very low flow rates, it may be necessary to pump the water level down as far as practical below the natural water table in order to have sufficient flow.

A water well is usually bored to a depth that is 20 to 50 feet below the water table. That is because you only stop drilling when you get sufficient water flow, or run out of money. It is unlikely that a hole with a total depth of 800 foot would be bored if the water table was anywhere near the surface. That would be a waste of tens of thousands of dollars.
 
  • #8
19,914
4,092
That is wishful thinking. You are very lucky to be living in an area where, when you dig a hole, it fills up with water. My water table is at 90m. I am only 100m ASL, but 10km inland.

Poorly fractured rocks have very low flow rates, it may be necessary to pump the water level down as far as practical below the natural water table in order to have sufficient flow.

A water well is usually bored to a depth that is 20 to 50 feet below the water table. That is because you only stop drilling when you get sufficient water flow, or run out of money. It is unlikely that a hole with a total depth of 800 foot would be bored if the water table was anywhere near the surface. That would be a waste of tens of thousands of dollars.
That all may very well be true, but the OP just wanted to know how to get water from 800 ft depth to the surface. He didn't say why he wanted to do this. We don't know the geological setting at the OP's site, but I agree that, if the rock is very tight, the drawdown at the well may be high. On the other hand, if the permeability of the rock is high and the rate of water removal is low, the drawdown may not be too much. As with many practical problems involving groundwater, the most important consideration is the geological setting (location, location, location).

Chet
 
  • #9
Baluncore
Science Advisor
2019 Award
7,407
2,452
Chestermiller. I believe we differ in our extrapolation from the OP question.
You are assuming the hole is full of water, but that the OP only wants to sample water from the 800 foot level.
My assumption was that the hole is dry above the pump at 800 feet, hence the deep hole and pressure problem.
 
  • #10
19,914
4,092
Chestermiller. I believe we differ in our extrapolation from the OP question.
You are assuming the hole is full of water, but that the OP only wants to sample water from the 800 foot level.
My assumption was that the hole is dry above the pump at 800 feet, hence the deep hole and pressure problem.
I'm sure that you are aware that, if you have a hole down to 800 feet, the hole won't be dry unless the water table is at least 800 ft below ground level. Are you aware of any geological settings like this, other than on the side of a mountain? I guess I did make the tacit assumption that the water table is not hundreds of feet below ground level.
 
  • #11
3,872
88
How to pull up the water which is 800 feet below the ground? How much amount of pressure to be applied ?

Can we use P = dgh


Reply me as early as possible?
You can not pull it up like that. Capillary force (used by high trees!) may work, but it's very slow.
A common solution is to push water up by putting the pump low enough in the well. For a detailed description see:
http://www.popularmechanics.com/home/improvement/electrical-plumbing/1275136
 
  • #12
Baluncore
Science Advisor
2019 Award
7,407
2,452
Chestermiller said:
Are you aware of any geological settings like this, other than on the side of a mountain?
Define mountain.
Unfortunately, yes. On one occasion, once the immediately available water was used, the very poor flow encouraged a driller to extend a hole by 50 ft. All the water then disappeared and the hole has been dry ever since. Plugging the hole will not improve the original situation. That was in arid granite country where horizontal unloading fractures provided the only flow.

I believe it is a mistake to assume that another's selected situation will be typical of your experience. The selected situation mentioned in the OP should be expected to be atypical, or it would not have been posted here on PF.

The OP refers to a well that has been bored to 800 feet or more. I question why that was done. It suggests that the water table is very deep in that case. I made that point in the last paragraph of post #7.
 
  • #13
meBigGuy
Gold Member
2,323
405
A lot of talk but no one has answered the simple question. How much force is required to pump water up from 800 ft. Frame the scenario any way you want to allow an answer to that question. Assume a 800ft water table.
 
  • #14
Baluncore
Science Advisor
2019 Award
7,407
2,452
meBigGuy said:
A lot of talk but no one has answered the simple question. How much force is required to pump water up from 800 ft. Frame the scenario any way you want to allow an answer to that question. Assume a 800ft water table.

Baluncore said:
You cannot pull it. You have to put the pump down the hole, then pump the water out. Each 30 feet of water is about one atmosphere. 800 / 30 = 26.66 atm = 387 psi.
That is about 2 foot per psi.
I revise my quick estimate to one based on; 1 psi = 2.3084 ft H2O
800 / 2.3084 = 347. psi.
 
  • #15
meBigGuy
Gold Member
2,323
405
  • #16
Baluncore
Science Advisor
2019 Award
7,407
2,452
The theoretical limit for suction of water is 32 feet due to atmospheric pressure. The practical limit is closer to 27 feet.

The advertisement shows the handle at the top, but not the pipe that carries the many pump elements that you must lower down the hole.
 
  • #17
meBigGuy
Gold Member
2,323
405
Last edited:

Related Threads for: Water column and pressure

  • Last Post
Replies
21
Views
2K
Replies
36
Views
89K
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
2
Views
2K
Top