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Water tank level control
I have a underground water tank and a above ground tank at home and want to control the flow of water between them based on levels.
By Martin Wulff on 13 November, 2006 - 11:20 pm

I have a underground water tank and a above ground tank at home. The above ground rainwater tank overflows into the underground tank. When the above ground tank falls to 50%, I want to pump water from the underground tank to fill the above ground tank assuming that there is water in the underground tank to pump. I want some sort of indicator that will tell me the levels in my two tanks. At the moment I have a pump that I manually control. The underground tank is 6ft deep and the above ground tank is 7ft. Any ideas of the best and most cost effective way to go about this.

Thanks in advance

Here is a general solution Martin. I would go with ultrasound sensors, one in each tank, pointing down from top of tank. I am assuming that you want eletronic display of tank level, either full/empty type display or continuous display of analog level. I think the banner engineering ULTRA-BEAM sensors would work pretty good. The cool thing is that you can get either analog output (more money) or descrete outputs on the Banners. You can get the functional job done either way, it's just how much info you want to buy for your system's display.

Anyway, I would run both of those inputs into one of the new Horner graphical PLCs (check them out at I have not used them, but if you want electronic graphical display (whether digital or analog) that would be a pretty good way to go, I believe. I understand that the software is free, but again, I have not actually used these before. I believe the Horner has an analog input if you decide to go the continuous level display route.

Hope that helps Martin,


I have a simple application of water filling. When water fills the tank, I want to put the motor off.
I have a float switch and a relay.

Can anyone help? A schematic or any wiring diag. would help. Thanks.

Simple, I am assuning when you refer to the motor, you are reffering to the motor driving the pump which is filling your tank. If so, you would just use your float switch and relay as a remote stop for your motor, wiring it the same as any stop button on a motor control circuit. i.e. When the float switch is energised, the relay is de-energised and hence the motor will not run, and oppositely when your float switch is not energised the relay will allow the motor to start. There is a few variations on how you could do this.

By LAMIN TURAY on 7 June, 2007 - 11:41 pm

Well I am not actually referring to this exact method, nonetheless they are both very similar.
Mine seek for one that uses the float ball whose assembling acts as a key for an electrical that open & closes in order that the pump would be energised or de-energised.


By Michael Griffin on 9 June, 2007 - 2:42 pm

You need a float switch (A) at the 50% level in the above ground tank to turn the pump on. You need a switch (B) at the 100% level in the above ground tank to turn the pump off. You need a switch (C) at the 0% level in the underground tank to turn the pump off (in case the tank gets pumped empty). You need a relay to wire the switches to in order to control the pump.

You wire the switches so that A energises the relay when the float falls down. When the relay energises, one of the relay contacts is used to seal the relay in (so now the state of A doesn't matter).

When the float for B rises up, or the float for C falls down, it breaks the relay seal-in circuit. When the relay de-energises, the pump stops.

A R1
R1 B C |
---| |-----|/|----| |---|

I hope the ASCII art is understandable.

I can't offer you a good inexpensive suggestion for the level indication. A dip-stick might work for the underground tank, and a sight glass (clear plastic tube parallel to the tank) might work for the above ground tank. The other possibility is to just add several more float switches at different heights and use them to turn on indicator lights.

Could you please explain this system to me in a more detailed form?

Thank you,

By Michael Griffin on 3 January, 2008 - 11:05 pm

In reply to selam: I happen to think the original explanation was fairly clear and detailed, with even a sample circuit shown. Can you phrase your questions in more detail?

There were two separate problems discussed (pump control and level indication). Which are you interested in? What is it you don't understand?

You can use two T434R Tank Units from Anadex Labs ( ) to provide you with the required water pump control function and water level indication.

Install the one T434R at the underground water tank. Install the other Tank Unit on top of the above ground tank. Connect the water pump through the relays in each of the Tank Units, so that the pump will start and stop when the water level in your above ground tank reaches the desired level. These trigger levels are set on dials in the Tank Unit. The Tank Unit at the underground water tank will protect the pump from starting if the water runs out.

These Tank Units also have the capability of using a wireless signal to update a water level indicator that can be located up to 300m away. The wireless R5 Command Module can simultaneously display the levels of up to 5 water tanks. The water levels are displayed on 5 - 10 element LED bar graphs.

The easiest way of doing this is using simple level switches (my kids made the same type of switch using aluminum foil to close the contact then the level reached a certain height). In the underground tank have at least a low level switch to stop the pump.

On the above ground tank have a indicator at 50% and one close to the top to stop the pump from overflowing the tank.

With some simple relay logic you can automate your pump (tie in the overload relay in the circuit). You need 3 level switches (NC above tank at 50%, NC above tank at Max Fill Level, NO Underground Min Level)

Use multiple indicators or a delta Pressure gauge / input for water column indication.

The simplest and least expensive way would be to use float switches. It will be the same type you find in septic and gray water systems. Any good sized plumbing supply, or agriculture supply store could be able to help you.

By Michael Batchelor on 15 November, 2006 - 11:42 pm

Do you need remote indication, or can you just look at the tank and be satisfied?

If you can just look at the tank then rig a float assembly, something like a discarded lobster or crab pot buoy with a stick, on the side of the tank, and see how far up the stick floats. (This from a old farm boy. It works, and it's cheap, cheap, cheap.) Everything beyond this is more expensive but may be prettier.


There are many different ways this can be done. here are some options.

cheapest: find a float switch (many submersable pumps are already equipped with this) these pumps run about $300 at Canadian Tire or any hardware store. You can hang the float switch at the point you want the pump to come on. You will not have an indication of level with this. For really cheap use a dip stick.

More expensive: Find a small ultrasonic transmitter with relay contacts. There are many versions on the market that are no bigger than a baseball that will give you a level readout and provide a contact relay that can start and stop your pump at chosen levels.

This is more expensive. I am not sure of the cost but could be close to $1000 or more. It could also be less than that but I am not sure. If you are interested let me know and I will bring some info on the product home with me and can even give you a contact person to talk to if you are in southern ontario.

These two are your best options I think.

for water sensing, see this circuit, It might be another point of view:

Do you want to just control the pump or do you actually want to know the current level measurement? If you just want to control the pump, I would recommend to use level switch. There are two approaches in that too, you may want to go either for top mounted or side mounted. Depending on the mounting, suitable technology can be selected. Either float type, vibrating fork type, etc.

Hope this helps.


Connect your pump to the under ground tank. Run the above ground into the under ground tank by disconnecting the pump line and running it to the under ground tank. Make sure to put a valve inline between tanks so you can control the flow.

Regards Wayne

You can make a capacitance type transmitter quite cheaply. For a probe use teflon insulated wire with a weight on the end and sealed with a good quality silicone.

I forget the part number of the analog chip that converts capacitance into voltage but I'm sure if you do a web search you will find it.


I would use float switches to fix this problem. It is the easiest way to go. has some you could check out.