Float Level vs Conductive level

Dear,

I am working on a project that pump water out from a existing well and send it to a high level reservoir.
From the high level reservoir, booster pumps are used to feed water to certain area.

I was wondering what option is better to use: float level or conductive level. Which ones last longer and which one is easier to install on existing systems.

First, I believe conductive level switches will last longer since they don't have any moving part like float level switches.
however, float level will be easier to install on existing system since they don't require power, I believe a minor modification on the existing system like to have interlock with high level is to have float level switch contact in series with the starting of the existing pumps.

I really appreciate if you have any feedback on the above issues.

thank you!

Charbel

In my experience I have seen conductive level switches most on clean water applications and float switches most on wastewater. The relay for the conductive level is usually mounted in a panel, and only a low voltage applied at the rods, which really isn't much different from a float switch.

I agree with Tom.
I always see people using conductive level probes (hanging type) with level relays for level detection in wells.

http://www.carlogavazzisales.com/pdfs/sensorsprod/vh1q.pdf

If your're using float switches, make sure that they are the enclosed style used in waste water,



not the open style (on a rod) which can get dirty and hang up.

Tom Jenkins said:

In my experience I have seen conductive level switches most on clean water applications and float switches most on wastewater. The relay for the conductive level is usually mounted in a panel, and only a low voltage applied at the rods, which really isn't much different from a float switch.

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I agree with Tom. Conductive with clean water and floats with dirty water. If there's a chance of buildup, i would steer clear of the conductive types.

Hi,

I have never used a conductive level switch, but if these are the choices you have, I would go for that.

I have used two other alternatives:

1. Vibrating Fork. Rosemount or Endress Liquiphant are two good makes.
2. Cheap and simple. If your water is not pressurized or moves a lot, you can just use a single pressureswitch. Alternatively a pressure transmitter or even differential pressure transmitter.

Conductive switches need to be matched to the fluid. for example they don't work in pure water (as used in the semiconductor industry) at all, Theres virtually no conductivity. But even water that has has some time to settle out can be problematic if its really clean. I have had this problem in slow filling sumps when I wasn't careful. You can select different levels of conductivity so keep that in mind.

For dirty sewage water we use a 2inch dip tube with a small pump pumping air down to the tube and a pressure transducer to a plc or vsd to measure the back pressure in the tube which is proportionate to level - its better than floats in sewage systems and works very reliably.

The old german company (ABS Pumps) now part of the sulzer group did a pump and pressure switch system like this (many years ago) called a Pneumostat Level control.

Oh yea, a bubbler. I remember those. Ours used a little diving bell looking thing.

Lately I have been using Signet hydrostatic level sensors in both clean water and dirty water effluent applications. I've found them to be reliable and they are not significantly more money than high quality level switches. The 4-20mA output provides continuous level feedback and the span is adjustable.

Submersible (goes on the end of a stand pipe) and side wall mount for tanks. I've got one application with the submersible model where the sensor is actually sitting down in mud at the bottom of a deep sump and it's been providing reliable level indication like that for almost three years.