level switches in dewatering wells

Charbel

Member
Join Date
Jan 2012
Location
Beirut
Posts
307
Dear,


I need to measure level in wells (40 meters deep), with diameter of 30cm, I have added an hydrostatic level for the measurement of level with trip amplifier/signals splitters to get low level switch. However, in case of malfunctioning of the level transmitter, we need to use a back up for high level, a switch in the well.


wells also include a dewatering pumps, so we don't have a lot of space in the well.


What do you propose type of level switch for high level in the wells which should not exceed 2 meters deep maximum from the ground level.


thank you so much!


Charbel
 
Must of my level sensing is done with a Conductive level controller and a two 6 mm stainless steel rods isolated with some shrink wrap, it cheap and efficient :)

Here is some info on the last controller I used.
 
I can't believe a well is only 1 foot in diameter? That's crazy, I thought more like 5-6 feet maybe. If you are allowed, could you send me a picture or pm. I always imagine the stone water wells that are so wide.
 
I can't believe a well is only 1 foot in diameter? That's crazy, I thought more like 5-6 feet maybe. If you are allowed, could you send me a picture or pm. I always imagine the stone water wells that are so wide.

There's not much to see above ground... just about a foot of steel pipe from the casing with a flange on top, and the riser pipe through that flange, that conveys the product water out.

Have a peek on Google for "water bore diagram".

What i really hate about something that is installed 100-150 metres below ground is when you have a problem. Its several hours with a crane or drilling rig just to lift it up. Each section of riser pipe needs to be unscrewed as it comes up.
 
There's not much to see above ground... just about a foot of steel pipe from the casing with a flange on top, and the riser pipe through that flange, that conveys the product water out.

Have a peek on Google for "water bore diagram".

What i really hate about something that is installed 100-150 metres below ground is when you have a problem. Its several hours with a crane or drilling rig just to lift it up. Each section of riser pipe needs to be unscrewed as it comes up.

Oh okay, I see, I never would have considered those to be wells; that's pretty neat though, seems very difficult to work on as you say, but very interesting on how it works.
 
level switch in borewells

dears,


thank you for your replies, conductivity switches seem a good idea, however, I have another problem to solve, or another challenge to overcome, the level switch should be almost around 1km (980m) from the PLC, so any idea, I guess it should work with multipair cables shielded or multicore cables with 3x2.5mm2 diameters
the above case is only applicable to one well. the distance between the remaining wells and the PLC is less than 600m


thank you!
 
This looks like a job for a wireless transmitter. Assuming the pump is downhole you would have power available. Banner and others make remote I/O wireless units.
 
thank you all for you replies.


yes, this is an apron area in an airport, so we are not allowed to include above ground panels. Sometimes, we need to pull long distance cables between sensors and PLC, what I am doing, I am increasing the cable size from 3x1.5mm2 to 3x2.5mm2 to ensure that the signal reaches properly.


Between the PLC's and the servers, I am using wireless connection, however, between all the wells and the PLC's I am using wired connection.


the client asks for having a redundant level transmitter along with the one included in the design (hydrostatic level transmitter), I looked at the option of using conductive, however, it is not possible, since the level to be measured, is above 15meters (I was wrongly notified about the 2meter depth), so what I need to do is to use another hydrostatic level transmitter.


I am not very confident of using another hydrostatic level transmitter, since basically both have the same life span, so when one will fails, the other one will fail at almost the same time. So I am not sure, and I am not sure if there is another way to measure level considering that the new wells diameters are around 30 cm but the existing ones are smaller 15 to 20 cm.


total depth level is around 40meters


thanks,
 
I assume your hydrostatic level transmitters are the submersible style:


submersible-level-transmitter.jpg

Because they run cool in groundwater, they have a very long life span.


The problem is that they need an atmospheric reference port - tubing that runs from the transmitter up to the top of the well.

Being in cool ground water, moisture will condense out of humid air when the tubing is cooler than the dewpoint of the air in the tube. Over time, the moisture can collect into droplets and run down to the bottom of the sensing tube. The hydrostatic weight of the condensed water on the 'low' side of the sensor will generate a level value that is lower than the true level.

The work-around is the use of a desiccant at the top of the well that is supposed to catch moisture before it gets into the tube.


Noshok-Drierite-Drying-tube-desiccant-cartridge.jpg

Two different brand/models would give you some diversity to avoid the risk of common mode failure, but the sensing/electronics is really reliable; it's the moisture that's a problem.
 
Last edited:
You could still use a conductivity switch is if all you need is a backup high level alarm. The part that goes down the well is just two small electrodes on a cable, with a switching relay up the top. You will need a small enclosure to house that though.

The likelihood of both sensors failing at the same time because of being the same age is low. Hydrostatics fail when they sustain physical damage to the diaphragm or don't have the breather tube protected against moisture ingress.
 

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