Well water level and the physics behind pump lift..can you defy gravity?


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Old 05-11-13, 11:48 AM
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Well water level and the physics behind pump lift..can you defy gravity?

Well, (pun intended), I have a question, for the forum members, on a small irrigation well.
The well is approximately 25 years old, 165 ft deep and was cased with 2 inch plastic well casing pipe. Soil in this area is alternating clay / sand layers, no rock what so ever. A top side check valve was installed and 2 inch suction pvc was connected directly to the pump.

When originally drilled, the water level was approximately 12 ft below surface grade, and was pumped using a shallow well jet type irrigation pump. Results were not spectacular due to the lift height, but sufficient volume/pressure flow was generated to run 7-10 pulsating sprinkler heads at the same time. I estimate flow was approximately 15 GMP at 30 psi.

In the past few years, we have had persistent drought conditions, and this year, the water level in the well has fallen to 23 ft below ground level. This water level drop is near the outside suction limit of the pump (25 ft max) and the pump is cavitating, and water flow is no longer sufficient to run even 1 sprinkler head properly.

I know the well is good and has sufficient recharge capabilities, as I used compressed air to pump the well for good period of time, at a high volume level, so long as I could supply air to it.
Drilling a new well with larger casing for a submersible pump is not an option at this time.
Using an air pump system, to pump the well to an above ground temporary storage tank is not an attractive option either.

I have installed 1 ╝ suction pipe, inside the 2 inch casing, with a foot valve 60 ft into the well in hopes of being able to improve pump lift with a flooded suction pipe, but have concluded you cannot defy physics and gravity.

I am, however, hoping to use physics to defy gravity and this is where I ask your opinions.
I know a 2.31 ft column of water is equal to 1 PSI.
What I am considering is to use forced air pressure in the outer casing pipe to create artificial lift in the inner suction pipe, to force the water up the suction pipe closer to the surface using the pressure imbalance, where the pump can then lift it. I have calculated that a 10psi charge should be sufficient to lift a column of water 23 ft.

The math says this will work, but assumes the bottom of the well is like a closed chamber, where the water cannot escape back into the well when external air pressure is applied. I know, in reality some amount will be forced back down the well, but am hoping the static pressure of the water pocket will act somewhat like a closed chamber.

Before I undertake re-plumbing the pipes to do this, I am seeking your opinions on the above question.
I have not found anything on-line, discussing anything even remotely like this approach.

Thanks for the long winded read.
Dialtone_n_TX
 
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Old 05-11-13, 12:43 PM
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There are 2-pipe systems that use an above ground pump that forces some water back down into the well to help lift the water.

I do like your idea though.. as long as you can get a decent seal and dont have to worry about blowing apart some pipe section inside the well. I dont know the math either, but I would think that the water would just want to rise up the line (easy resistance) and not be forced back down into the aquifer etc. At the 'bottom' of the well is enough pressure to push water up 140ft, in your case.
 
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Old 05-11-13, 01:16 PM
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I am aware of the system you refer to, it is called a deep well jet pump system. Those are limited to around 45 ft maximum lift and would do, except for the fact I do not think they will fit inside a 2 inch casing. Also, they are not suited for my irrigation application. They are more suited for a home application where a large, continuous volume of water is not required.

I am glad to see you see my logic and will closely follow other comments and/or suggestions.
Thanks for the encouragement.
 
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Old 05-11-13, 01:57 PM
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Interesting, but I think the added pressure would lower the standing water level. You mention clay and sand and NO rocks. You couldn't ask for an easier DIY to drill your own well. Never done it, but a quick search indicates many have.

Bud
 
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Old 05-11-13, 08:00 PM
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I have looked at all those DIY well drilling videos and agree I could do it, and have considered that possibility.
This area has many home wells around 40-50 ft deep, shallow water table is around 15 ft from surface..
When mine was drilled, the driller said the shallow wells work fine for single home use, but the sand water bearing pocket was only 2 1/2 ft thick and would not recharge fast enough to use for irrigation.

My neighbor had 4 shallow wells drilled and tied them together at the pump, but has always had issues sucking one of them down to he point it starts pulling air for a few seconds till it recovers. I think the driller placed them too close together and they are pulling from each other, starving one or another of the pockets. His point spacing is only about 20 ft apart. If i could figure how to balance the draw from multiple points, it might work but is a lot of effort for a gamble. Farther spacing of the well points should not be an issue as my lot is 200 x 200 ft
 
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Old 05-12-13, 05:29 AM
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Just thinking, and I hate when logic won't let me agree. But if you pressurize the well, won't you slow down the wells ability to recover? Seems to me that initially you would get a rise in water, but it would cannibalize from itself instead of pulling from the surrounding aquifer thus needing an even greater rise to get to the top.
 
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Old 05-12-13, 08:39 AM
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with the 2" casing, the most water you will get out of it with a 23' water table is a deepwell jet pump (probably 2-stage Goulds sj10 with a larger sized nozzle in the jet).. would use a single pipe packer jet assembly. u really don't have any other options, other than the holding tank which u don't want and I don't blame u. Good luck.

not sure where u got the 45' maximum lift, believe its more like up to 100'
 
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Old 05-12-13, 09:52 AM
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Have you addressed conservation methods to water with less. Broadcasting water into the air requires far more volume than a soaker system.

Bud
 
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Old 05-12-13, 10:19 AM
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Packer system. I think they make inflatable ones now.
 
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Old 05-12-13, 08:40 PM
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Thinking more on this..
You need to figure the inside dia of the well casing (2") minus the outside dia of the water pipe (was it 1.25" ID ?). This would give you the exposed 'surface' area of the water that will have air pressure applied, in sq inches.
So, 2" dia is 3.14 sqinch and lets guess the water pipe is 1.5" OD .. so 1.77 sqinch. The surface remaining is 1.37 sqinch.
If you were to apply 10psi to the well, you would have (10/1.37) 7.3 pounds of force applied. This should result in lifting 7.3 pounds of water up the inside pipe. I found a table online that says weight of water per foot in a pipe is 0.341 x d^2. So that gives us 0.53 pounds per foot. Works out to about 14ft of lift.
 
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Old 05-13-13, 03:53 AM
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Not that I "know" , of course.. lol. Im just putting together the physics bits that I found. It seems logical. After all, thats how a reg surface pump works.. it removes as much atmospheric pressure above the water inside the water pipe as it can ,and the atmos pressure on the well water surface pushes the water up the pipe. (And hence, the limit of 34ft as this would need a perfect vacuum from the pump side for the atmos to push it up that high).

Also, dont forget that as you use the water and the level drops, you need to replace that air pressure as well as push the water higher. How much extra air you would need would depend on the recovery rate of the well vs how fast you are using the water.
 
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Old 05-13-13, 05:24 AM
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Dave, you say "the atmos pressure on the well water surface pushes the water up the pipe." It isn't just the surface inside the well, but the entire water table below that is somehow connected to the atmosphere above. Applying pressure to the well will simply force that column of water lower. The added height you are suggesting for lift would be that same distance getting the water back to the level it started. If you were working with a closed vessel, then you could indeed pressurize it as you are suggesting. But just as a vacuum lifts that water column, pressure will push it down.

Bud
 
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Old 05-13-13, 05:57 AM
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You need to go to a packer style jet. Make sure you match the jet to the pump. If you desire a lot of water look at the sta-rite MSE series, anything 1-HP or above. You won't be able to pump near as much water as the irrigation style pump but you'll be able to pump some, which is better than nothing.
 
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Old 05-13-13, 06:22 AM
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Read here on the packers from goulds pdf....

http://media-cache-ec3.pinimg.com/19...fe1cd8d517.jpg
 
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Old 05-26-13, 04:34 PM
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Thanks to all that responded with alternatives.
I can now report back that pressurizing the outer casing DOES NOT have any dramatic affect on the static water column height in the suction pipe. If I got any lift at all it was only around 2 ft with 25 PSI applied to the casing pipe.

Sorry it took so long to report this back but oddly enough, it has rained the last 3 weekends, not a lot, but just enough to muddy things up and make the grass shoot up. And if that was not bad enough, my lawn mower decided to throw a bearing in the mowing deck with the yard half cut.

Go figure.

Thanks.
 
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Old 05-26-13, 08:05 PM
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Im curious if you were able to hold the pressure at 25psi ? If you took off the air supply and put a gauge on the well, would you have 25psi and did it drop quickly or slowly ?
Assuming its a sealed system, then the water column must have gone down (no way to measure it while sealed though) and into the aquifer ?
 
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Old 05-29-13, 07:40 PM
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Yes, I can hold the pressure steady for some period of time. Approximately 15-20 minutes or so. It does fall off slowly, but I was not terribly careful with the seal on the casing pipe, so it may have a small air leak I did not detect.

For those wondering, here are a few curious results I noticed.
1. When first applying the air pressure, with the pump running, there is a short time period pump output increases noticeably. This rapidly falls back off to normal. I assume it is a temporary condition caused by forcing the water column down the casing causing a temporary water column rise in the suction pipe.
2. When discharging the air from the casing with the pump running, pump output drops to zero for a short period, then returns to normal. Again, I assume it is a result of a temporary drop in water column height in the suction pipe when the water in the casing rebounds due to the rapid pressure release.

In essence, the theory holds up but only for a few seconds till the pressure offsets equalize.
 
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Old 05-30-13, 04:02 AM
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Not that its going to be effective to use, but in theory then..

I wonder if you were unable to keep the 25psi held while the water level dropped ? I would think the water level starts dropping pretty fast as the pump removes the water. Maybe it's a lack of cfm (air flow) ? A decent sized pressure tank at 130psi beside the wellhead regulated down to 25psi/etc might help.

Thanks for reporting on it.. interesting subject..
 
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Old 05-30-13, 05:56 AM
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Water is being forced UP the casing by the pressure of the aquifer. The column in the well is "balanced". If the pressure in the aquifer was great enough, the well would be flowing artesian. When you add pressure to the casing you are now pushing back on the aquifer and the column should drop an appropriate amount.

Interesting experiment though.
 
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Old 05-30-13, 05:34 PM
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Yes, I could keep a steady pressure for some period of time. I did install a new air gauge to see what it was doing.
When charging the air, I had to refresh the initial charge a few times till the pressure stabilized as the water was pushed down in the casing. This only took 3-4 air refills in the first 10-15 seconds before air pressure leveled out to an initial steady state. After that it dropped off slowly over the next 15-20 minutes (I assume a small air leak somewhere.)

Before I did the air trial, I placed 100 ft of suction down the hole to assure it never would be in the area past where the water was being pushed down the casing at the pressures I was using.
I sealed the top with a rubber transition with spiral hose clamps (2inch to 1 1/2 inch) like is used for Drain-Waste-Vent transitions. It held pretty good at 25 PSI without ballooning too much, but I would not want to try pushing it much past that. I used it since it was relatively easy to install and ultimately remove. (I got tired of digging/cutting and re-gluing my pipes)

It was a good experiment though, but now I need to face reality and start looking at either a packer deep well system, or just get a driller to punch a new hole large enough for a submersible (which I should have done in the first place).

Either way, I think I am in for a case of sticker shock as the original was drilled 25+ years ago and my guess prices have risen accordingly over the years.
 
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Old 05-31-13, 07:23 AM
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What location are you? Here in the Houston area a 100' 4" well is in the $3500-4000 range.
 
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Old 05-31-13, 05:22 PM
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I'm in the lower Rio Grande Valley area (Harlingen, Brownsville, McAllen).
 
 

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