Static Water Level in Well - Stone Drop Method

[Pete Judd]

A piece of strafoam with a fishing weight attached to a string will get the thing done , if it is a clear shot down to the pump. I have plastic plates every 20 feet to deal with the twist of the pump all the way down, so dropping a rock down would not work. Get your fishing reel out,as well as your tap mesure.

 

[NorTracNY]

As posted before. distance equals .5 * 32.2 * time * time so 56' would be 1.865 seconds. The problem is this doesn't handle the drag of the stone (probably not much for this case) nor the extra distance traveled if it bounces around in a pipe (could be very significant).

 

[piller]

The first reply is about using a bubbler or pressure system to measure water depth and that is a good method.

I like the suggestion about using ice cubes instead of rocks.

I think what would work would be for the original poster to "calibrate" his measuring system for his specific situation. Use the same size ice cubes, released the same way. Use the same method to measure time. Use a line to measure water level accurately when the water is at different levels. Make several measurements and determine your consistency and margin of error.

 

[Brad_Blazer]

From the earlier Wikipedia link: "Please note that in this article any resistance from air (drag) is neglected."
Here is a more complete discussion that includes the equations for velocity but not position with respect to time for a falling object in air. Of particular note is this quote:
"The hyperbolic tangent has a limit value of one, for large time t. In other words, velocity asymptotically approaches a maximum value called the terminal velocity "

http://en.wikipedia.org/wiki/Drag_(physics)

Happily I found this calculator that includes drag.
Freefall with quadratic drag

Still neglected is the significant effect of the stone hitting the sides of the well. I think the drop method really needs to be calibrated for your particular well using a standard object. If you can make ice cubes of consistant size, shape, and weight I like that idea. Calibrate at various depths by comparing to direct measurements and make a reference table. You can drop several ice cubes and use average times to improve accuracy.

Pete Judd's direct measurement using a floating heavy object on a fishing line sounds great although I would avoid using a lead fishing weight since there is always a risk of losing it in the well.

On a related note there is also a lot of info out there on falling pennies such as Mythbusters season 1 episode 4 and this paper:
The Penny Problem

 

[Carl_NH]

Brad, Pillar & all,

I have done additional testing now. Measured the static depth 56' dropped a stone took 3 sec dropped ice cubes took 4.5 sec (larger mass & lighter)


I did another test at around 80' and was 4.5 sec stone drop, and 7 sec ice cubes - I say around 80' as the pump was off and the well was in recovery mode of 5 GPM so from the time of the measurement to dropping the ice cubes and stone was 2 minutes or maybe 7-10' of depth reduction.

I have since spoken to the well driller/pump installer and they concur it's roughly 18' per sec with a small stone..

Thanks for all the replies.

Carl

 

[wrooster]

Brad, Pillar & all,
I have done additional testing now. Measured the static depth 56' dropped a stone took 3 sec dropped ice cubes took 4.5 sec (larger mass & lighter)

weight has NOTHING to do with how fast an object falls due to gravity. furthermore -- air resistance, for an object with the density of water or greater, does not appreciably come into play in the equation until after about 4 or 5 seconds of freefall.

your numbers are so all over the place that i would not trust any of them.

wrooster

 

[wrooster]

I have since spoken to the well driller/pump installer and they concur it's roughly 18' per sec with a small stone.

so:
1) your driller drops stones into a well casing to measure depth? they must sell a lot of replacement pumps this way.
2) get a new well driller, one that doesn't drop stones into a casing, has the proper depth measurement equipment, and has some knowledge of physics.

wrooster

 

[mchildress]

Man you all are sure making it complicated I have always just tied a nut to the end of a string and drop it down the casing until I hear it hit water. Tie a knot in the string and measure from the knot to the nut. I liked the fishing pole idea though,the ice was pretty cool too.

 

[Kays Supply]

I don't work on very many pumps any more but have been doing it for 30+ years. I am not up on the CSV. I have just put a pressure regulator in line. I set it to provide just enough presssure to activate the high side of the switch. While running and letting a small flow out I set it and the switch. The pump runs as long as a small flow is going out the discharge. When you shut the flow the pump builds up to the regulator setting/ switch setting and shuts off. You buy a pressure regulator sized to your pump and flow needs. Jacuzzi sold this as the " Aqua Genie". We just made our own. I have them in cysterns and deep wells.

 

[SPYDERLK]

Brad, Pillar & all,

I have done additional testing now. Measured the static depth 56' dropped a stone took 3 sec dropped ice cubes took 4.5 sec (larger mass & lighter)


I did another test at around 80' and was 4.5 sec stone drop, and 7 sec ice cubes - I say around 80' as the pump was off and the well was in recovery mode of 5 GPM so from the time of the measurement to dropping the ice cubes and stone was 2 minutes or maybe 7-10' of depth reduction.

I have since spoken to the well driller/pump installer and they concur it's roughly 18' per sec with a small stone..

Thanks for all the replies.

I didnt see it in the thread -- may have missed it, but Ill put it here anyway. The formula for distance is 1/2AT^2. The acceleration of gravity is 32 feet per second per second. A 3 second fall gives 16x3x3=144 ft. Depending on the density and shape of the dropped item, air resistance can become a large factor as speed increases. I would call 3 seconds about 110ft with a small rock.
larry