To Control the Water Level in a Tank

If you're just using tap water at low flow, a conventional ball float valve like the type found in your toilet cistern tank is good enough. If you're using a pump or an electrical mechanized valve to control the supply, then a 3-probe conductivity switch (1 long probe neutral, 1 short probe for high/cut off, and 1 long probe for low/cut in), or a float switch will do the job.

Or, have a float in the tank, a small rope/string over a pulley at the top, and a indicator on the side, 2 micro switches on the side indicator, for "start" and "Stop" at the set levels your looking for..

Or, if you have a "Sight tube/glass" with a ball inside, then a optical sensor either side of that tube, so the "ball/indicator" breaks the beam and starts/stops your pump, rings the bell, wakes the hampster...

NOw another question! What type of logic or control we can use to ON and Off the motor when we get a signal from the Level Sensor. Give me the optiona available

Greetings,

I would suggest using "set - reset" type logic if you are using a microprocessor based control.

Ladder logic can be programmed using a "rising-trigger", "one-shot-rising", or simple "set-reset" bit logic.

With function-block programming use the "set-reset" function block available in the software library.

If you are not using a microprocessor and want to use simple hardwired probe control; Procure an inexpensive level controller such as a B&W inductive probe unit rated for the voltage & frequency available at your location, then connect the wiring per the included directions and you should be in business. The distance between the "high" probe and "low" probe determines your tank level.

It is possible to build your own OEM level controller by using a high-impedance relay with "normally-open" and "normally-closed" contacts by wiring one of the contacts as a "hold-in" circuit through the low level probe. Hence; whenever the water level covers both probes, the relay coil is energized and is held in by the "seal-in" contact until the water level drops below the low level probe at which time the relays coil is de-energized, the normally-closed contact is the actuated and the pump or valve is energized and runs until the level reahes the upper (high) level probe. Brass will also work well for probe material.

If you need a connection diagram or other information please feel free to contact me via email and I would be most happy to send you any information I have access to.

Good luck!

or a light weight switch.

where the control arm can switch with low force, run your string through a loop or hole in the switch arm and knot the other side, then a weight on the end of the string, and the weight of the float enough to throw the switch.. so..

Water level gets to High set point, the string pulls the switch down and the pump goes off

Water level gets to Low set point, the string pills the weight up and the pump starts running.

PLC, replace switch with flags on the string, flag goes past lower set point, turn pump off, flag goes past other setpoint, pump goes on...

Toilet cistern floats.. drill 2 holes in side of tank, place float into hole, and seal it so you can place a switch on the arm, when the top float rises above a point, turn off pump, when bottom float drops below a point, turn on pump..

Sighting glass (glass/plastic tube running from outside tank from bottom to top)

place a small rare earth magnet inside float, place a reed switch on the outside of the tube, 1 TOP and 1 Bottom, wire as per set points above

not using rare earth magnet, optic sensor on tube, wire as per above..

alternative to pump..

when water level drops below a setpoint, display a picture of a car accident, have 2 Lawyers tied to bikes and they run the pumps, the 1st one to fill the tank the most gets the job, same can be used, dangle a donut in front of some police people (but it would mean they get fit more than get fat) or a machine that flips down a sign that said "not broken, please don't touch" in front of some engin...... ummm won't go there...

Didn't we have a thread that dealt with lubricating bearings on some device that was burning them up from high temperatures? We might need some special bearings on those bikes. Great thought.

When the tank level falls below the low level setpoint, turn the pump on. While the level is rising, maintain the pump on until the level hits the high level setpoint, at which time turn the pump off until the low level setpoint starts it again.

Repeat ad nauseam.

Simples.ζ

Or even simpler:

100 IF(LEVEL<LOW_LEVEL_SETPOINT) THEN 200 ELSE 100

200 TURN ON PUMP

300 IF(LEVEL>HIGH_LEVEL_SETPOINT) THEN 400 ELSE 200

400 TURN OFF PUMP

500 GO TO 100

Greetings, Macsimus,

I am curious, as to what costly design solution you have come up with. Would you mind posting back with the information? Thanks.

Not a complex one, very simple, to use a Ultrasonic Level trasduser to measure the level of the tank and to ON the motor when ever a set-bottom level is reached and to OFF when the set-Top level is reached. But the float method which you have suggested is inexpensive, right?

I'm not familiar with any float valves that would work in your application. The float valves that control the filling of toilet tanks work fine for a couple of gallons, but if one of those is installed at the top of your water tank, then the pump motor would be working on and off, repeatedly, to keep topping off the tank for just a few gallons.

It would be helpful if we knew the gallon capacity of your tank, and how it is filled. Does the tank have an input (fill) pipe, separate from the take-out (discharge) pipe?

Depending on the size of your tank, a simple pressure switch might be used at the bottom of the tank to control the pump's motor.

Skeeter dear

if its a domestic pump,using 0.5 Hp or 1Hp motor (220V ) then the cost of a controller would not not exceed Approx US$ 8.00 for a 1 Hp motor using a CONTACTOR and US$ 5.00 for 0.5 Hp motor using a 10 Amp RELAY.

Controls available are THREE wire rooftop tank water level sensing with STAINLESS STEEL sensing probes ( as DC potential 3/4 volts are used the only weak point ) auto sensing of water level say when level is down to 1/2 of the tank and start, stops when level is full.

also senses ground level reservoir water level and if level is very low stops motor dry run.add a dollar and you can see the level of water in the tank too.

I know ; for one is running for 12 years at home and made one last week for a friend.most of the things are available in the junk box of any self respecting electronics tinkerer. I have cleaned the sensor probes twice in 12 years.if you find it difficult to procure stainless probes , use Carbon Rod from a D type Dry cell( Boil it in detergent) solder the top metal cap to normal thick copper wire insulated or otherwise and use as probe; electrlysis does not seem to have any effect on carbon.

try google you will find a dozen circuits but one published many years back in "Electronics for you ",an Indian Publication is the most elegant I found, using one,

smartest micro processor of them all named 555 !.

pkd

Your pressure transducer idea has many options available to allow you many different functions if used in conjunction with a programmable logic controller. However, as you have found, these systems tend to be rather costly.

Another type of level sensor would be a captive air system where you have a sensing tube in the tank. As the level in the tank rises, the backpressure caused in the tube will activate a pressure switch that will start the pump. As the level drops, the pressure switch will de-activate the pump, or vice versa if you are filling the tank. An altitude gage can be installed in conjunction with the tube. This will read the level in the tank in inches of water, if that is the calibration of the gage you get.

There are companies who furnish a complete system to do what I have described above. Sometimes there is a small air pump provided to continuously deliver air to the tube to compensate for any loss of air or leaks in the tubing connections. These systems are called "bubbler" systems.

Macsimus

I ment to write to you but by mistake addressed it to Skeeter,

skeeter knows it all.

apologies to both of you

pkd.

From p.k.datta...

I ment to write to you but by mistake addressed it to Skeeter,

skeeter knows it all.

apologies to both of you

Skeeter doesn't know it all, and never makes that claim, but he does know a lot. Skeeter just does the best he can in trying to help solve problems. Nothing more... nothing less.

Skeeter

please,please dont misunderstand, I would never make a comment which I beleive is not true ,at least not in these columns,when I realised I addressed to you rather then Macsimus,I thought it would be prudent to apologise;because I gave a very low tech basic example of what i made;and I know for sure having seen your few other correspondence that it would appear very elementary to you as well; it was in this context I mentioned Skeeter knows it all,it was not a tongue in the cheek comment beleive me.

regards

pkd.

p.d.datta,

Of course one of my fears was that it boiled down to a difficulty in communication. Your use of English resulted in often used idioms in the U.S. When we try to be condescending, we greet someone in correspondence by saying, "Skeeter, dear," (which is way to personal, and can be interpreted as a put-down). Instead, Dear Skeeter or just Skeeter are the common greetings. Then, you used the phrase, "Skeeter knows it all," which, again being a common idiom, means "Skeeter is a know-it-all," which is easily interpreted as being an offensive term. So, if the two phrases in question were simply examples of your not being aware of that they could be taken wrongly, then I apologize to you for my retort.

Skeeter

Also a GA.

Well put PKD. Good man. I gave you a GA as well....

p.k.datta, dear,

I've been thinking about your comment in the post in which you stated that, "...skeeter(sic) knows it all." Taken at face value, this is a stupid statement by you, so if you meant it to mean the way I've interpreted it, up yours!

Use a sump pump float switch, but, reverse the logic.

hello

i have a float switch in my house. it works perfect. very cheap very easy to install, u can control the level at which the pump starts to work by varying the length of the cable from the float switch to some kind of weigth that comes with it, right guys? i stand to be corrected! I have worked in industrial level before and we used the same kind of float switch for the water tanks (very large) so i think it can work both large and small scale

zack

The problem with float valves (even ones with a very long float arm to "measure a greater depth of water drainage) is that they "turn on" and open up incrementally (in the continuous sense) as the float drops. You have asked for refilling to begin when the water lever reaches a set point of tank-emptiness. In other words, you want the tank to empty out a predetermined level of water before any refilling commences--perhaps you don't want the tank water refilling to be cycling too often? I think there's a way to do this...but first, am I reading your question correctly?

Thanks

Pressure guages, sight tubes, optical sensors... you are making this way to complex. Two conductive sensors and a liquid level sensing relay will do the job - close contacts when the bottom sensor goes dry, open them when the top sensor gets wet. Conductive sensors perform the same job as ball floats, but are a lot more reliable for a myriad of reasons, one being nil mechanical movement.

There are plenty on the market, try http://www.multitrode.com/products/simplex_sump_packs/overview.cfm

If you want it simple then use a ball float valve. You can also use a electrical level switch, relay and a small solenoid valve. There no need to get more complicated than this on a home water tank I would think.

pipewelder

Good Day,

We have used some very inexpensive float level switches to stop and start a pump for simple R.O. systems. Two switches operate a contactor which in turn operates the motor. Here is a company that sells several to choose from:

http://www.omega.com/toc_asp/subsectionSC.asp?subsection=K13&book=Green

The low level switch (SW1) should turn on when it is at low level.

The High Level (SW2)switch should turn on when it is at High level.

The Contactor (MC1)should have enough contacts to Power the Motor and at least 1 aux contact to "seal in" the logic circuit.

The Logic would be.

(SW1 OR MC1aux) AND NOT SW2 turn on MC1.

or written a little differently:

MC1 = (SW1 OR MC1aux) AND (NOT SW2)

Then wire the contacts of MC1 to the motor. Note, look at you regional standards for hooking up the motor. you will need fussing and or an overload relay on the contactor to protect the motor and logic circuit.

I hope this isn't too simplistic for you.

Macsimus,

Potable water tanks for home can be controlled by standard 'sump pumps'. If you google this you will find many off the shelf suppliers that will do the job.

Just opt for a magnetic float switch. It provides signals for the motor and maintains water level in the tank. Quite cheap too.

This is an answer to your question unless. . . . you want to conduct a research.

As someone else said, simple is best.

Use a normal float valve to maintain the level and a simple pressure switch to turn off the pump when the float valve closes off and the pressure rises....

Nothing is simpler than that, used in probably half of the European caravans to supply hot and cold water to the kitchen and bathroom!!!

Do not forget the non return valve between the pump and the pressure switch to stop the pump cycling on and off for no reason.

Hello Macsimus,

I have not read any posts others have made as I have been away and have just switched my computer on, sorry.

From the phrases you use it sounds as if a 'ball-cock' float would work fine, as long as you have a small header-tank, which, in turn has a pressurised water supply. A ball-cock has a minimum and maximum level depending on the length of the float arm. Otherwise, a float switch.

'Simple' and 'basic' is not always a bad thing. It depends how dependable and reliable you want or need it to be. If you can design excluding electricity/batteries etc, there is very little to go wrong or break down when using a ball-cock.

jfmfit

Sorry to come in so late on this one.

Please all go back and read the guest post number 10.

Using a balcock and float valve system (While ideal for a "mains" supplied water source.) will mean the pump is functioning multiple "pressure cycles" while the last bit of the tank is topped up. That means that the contactors in the controller/pressure system are being worn out unnecessarily. From the original request, I'm understanding the tank should empty to a certain level before the pump is turned on and the pump should be allowed to run "open pipe" until the tank is filled back to the high water level. (Also means the pump is only pumping against direct head and not using extra energy against pressure system.)

The switch with a cable and free running "bobble" method activating the motor controller seems best for this. (Or high and low magnetic switches)

I've seen motor contactors burn out and also starter capacitors have a hard time from unnecessary continuous cycling.

run your line with a air header tank, this should solve your pump switching problem, think of it as a storage capacitor, put one on the house that I visit, runs happily off your car 12V battery ;o)

A ball cock system is easily modified to have a great "Hysteresis" if required, most have some anyway to stop the valve taking an age to finally shut off and not to open on a minor water usage......

On ones that I have recently installed, you just need to extend the vertical arm/guide that the float runs up and down to allow the float to travel between the lowest required starting to pump position and the top, stop the pump position.....really easy. A piece of plastic and a hot glue gun and its done......a real "No-Brainer"....

The beauty of such a system is there is no need for any "control" wiring to be run between the tank and the motor control......

Some people like complexity, I have been guilty of it myself, but the original poster did not even install it I believe and does not understand how to fix the present system.....we must keep it simple for him as simplicity saves money!!

Hello Andy Germany,

I agree with all you say! Keep it simple. People have used tanks for hundreds of years with various refilling systems, and, way before 'electricity' was invented. There is nothing to go wrong that cannot be easily replaced when using stop-cocks or similar.

I am in the UK and have not heard a term you use. 'Contractor', what does it mean please? The way I would use this work is with ref' to a builder etc as being the contractor.

I do not have a way of drawing my ideas for the www. But, can understand how all the answers given are probably not any help to someone who has never done anything like this remedy before? I have spent years as a builder and 'jack of all trades' and, one man band, and find there does seem to be a move to use complicated ways when, simple is not only easier but, is more reliable.

jfmfit

Please be so kind as to remind me in which post I used that word.

I did see the word Contactor (note the spelling difference!) in someone else's post, is that what you meant?

A Contactor is a sort of electrically driven switch, a sort of "up market" relay with heavy contacts, often used to switch medium sized motors on and off....

agreed..

My understanding.

relay, small currents/voltages

Contactor, high currents voltages

contractor, someone you pay a lot of money for a low quality job

Perfectly put!!!

Hi Andy,

I would like to intall a ball cock into a water tank with hysteresis, such that the ball cock opens when the tank is nearly empty. This is to avoid unnecessary cycling of a rainwater harvesting pump when used in an indirect system. I am not keen to use electronics to trigger the starting and stopping of the pump as this to me is complex and prone to failure.

Can you explain how you modify ball cocks in more detail?

Yorkshire Dave.

Here's a contactor removed from control box for regulated well pump. Two small lugs at top connect across coil (electromagnet), thence, in series, across the reserve tank pressure regulator and Nom 220 or 120 volt mains power. When reserve tank reaches "cut-off" pressure, the regulator opens circuit across contactor's coil, allows pump power switching across each of three 220V legs (the three large lug pairs) to break. Vice versa to energize pump and restore reserve tank pressure...or to run pump in unregulated mode, bypassing reserve tank. The installed set up is shown below. The one removed was open contact type. The replacement one is enclosed contact type...much less problem with insects cooking between and shorting contacts...the bane of many well systems. Size scale: can be held in one hand.

"Contactor" is also a term sometimes applied to DC applications, such as with starters on some farm tractors.

The easy way to add hysteresis to a ball cock switch/valve is to place a "leaky" reservoir/tank on top of the float, and arrange for the incoming water to fill it.

Ready made level controllers available in the market.Minilec -pune makes different types of level controllers for different liquids with probes.