Static water level measurement using air method...

[erkme73]

So I'm intrigued with the concept. I've read all of the threads I could find, and watched a few YT videos on the subject.

I understand the principle, but am curious about using it for a long-term maintenance-free application. And, since I'm a bit of a gadget geek, I was considering installing a pressure transducer so I could continuously and remotely monitor the readings (with the added benefit of receiving an alert/text message when the level falls below a critical level).

My well is 270' deep.
Pump is at approximately 250'.
Static level is currently at 44' below ground.
Recovery is a paltry 2.5GPM <--- and this is why the level is important to me. With 40+ min of water use, my well will run dry.

The plan would be to install a 250' line of 1/2" PEX-AL and capping it with a pressure gauge/transducer - flushing the line with air.

The question is, will that reading be dynamic and accurately trend with the in/decrease of water above the end of the airline? Since decreasing water level would mean decreasing pressure, I can only assume if the water level drops low enough, the air pressure will ultimately force air out of the bottom of the line (even if the water level is physically still above the end of the tube) and thereby screwing up any additional readings.

This is where I'm a bit fuzzy... If I have a known (tape-measured) static level, could I not just partially fill the tube (i.e. not expel ALL of the water), thereby allowing a margin so that if the water level drops to critically low levels, there's still enough of a water column in the tube to prevent it from completely purging? I'd have to correct for the pressure delta, but the linear 2.3' per PSI would still apply, no?

TL/DR: Ultimately, I'm after a way have a real-time, remotely-accessible way to verify the water level using the air line method, and just need to verify that I don't need to add air at any point after the initial charge.

 

[Reach4]

I think you will need to add air, continuously or continually. Maybe give a stroke or two with a tire pump when taking a reading.

You could use an ultrasonic sounder with a remote display. https://enoscientific.com/ww310/

 

[Sponsor]

 

[LLigetfa]

Whenever the water level drops, you will lose air so you need to constantly replenish it.

 

[erkme73]

Bummer. Yeah, I figured even if I didn't charge the line completely to avoid the air loss from the bottom, over time, the air under pressure would dissolve into the water anyway. US reader is a bit to rich for my budget. Is there a mechanical type switch that would shut the pump off when the water level approaches critical?

 

[Reach4]

Bummer. Yeah, I figured even if I didn't charge the line completely to avoid the air loss from the bottom, over time, the air under pressure would dissolve into the water anyway. US reader is a bit to rich for my budget. Is there a mechanical type switch that would shut the pump off when the water level approaches critical?

You could use one of the mechanical timers that have 96 little pins that you could set to turn your pump on for 15 minutes once or twice or more times per day. You can get an electronic timer to turn on for a number of seconds you select and off for a period you select, and repeat. You might need 100 psi at low volume.

You could also have a compressor with a tank that turns on as needed to refill the tank. Run a very slow flow of air from the compressor tank.

 

[LLigetfa]

...if I didn't charge the line completely to avoid the air loss from the bottom...

Doing so would give you a bad reading. For a true reading, the entire pipe has to be filled with air.

 

[Valveman]

There are devices that do this already. The Cycle Sensor looks for low amps caused by pumping air instead of water. When it detects low amps it shuts the pump off and displays the word DRY. Then you set the internal timer to restart the pump in a few minutes or up to 5 hours.

 

[erkme73]

Doing so would give you a bad reading. For a true reading, the entire pipe has to be filled with air.

Only if it's not properly calibrated, I think. Because the 2.3' per PSI is a constant, you wouldn't know the actual water level, but you could determine the delta from the baseline accurately. By compensating, it would be matter of physically measuring the level with a tape and then equating that to a given pressure.

So for example, instead of filling the entire 250' pipe with air (requiring 130 psi), filling it only half way, leaving a lower static pressure, but correlating that to a known measured SWL would only require a simple linear remapping on the transducer (or gauge).

The bigger issue is air loss due to absorption by the water, or overall effective range of the air column. By reducing the air pressure in the line, you may run out of usable positive pressure (i.e. vacuum) before the SWL reaches the critical depth.

I have an ethernet-based data logger that I will play with, and if I can get it to work, hopefully I'll remember to update this.

 

[Valveman]

I use lots of air lines in water wells. I have rigged one up in the past to give continuous readings. I used a small compressor and bubbled a little air in the line about 30 seconds before I took a reading. Decreasing water level will cause a loss of air that must be replenished to get a good reading.

I normally only use an air line for well testing and to check the accuracy of the Cycle Sensor.

 

[erkme73]

That makes sense. While I like the idea of know what the level is, and the rate at which it's dropping/refilling, ultimately, the most important thing is to protect the pump when my kids are having a water day outside and leave the spigot on for more than 45 min...

ETA: Thanks to Cary's suggestion, I have a cycle sensor on the way. That's cheap insurance.