Need to Automate Water Tank Level Control

Single float can have start and stop separate two switches for two sets of water levels (lower and upper limits) to start and stop pump. Switches trigger pump controller one at a time.

If you are keen in knowing about continuous water level monitoring or float based control then we are discussing capacitive continuous water level sensor in another forum and also float switch based water tank controller on CR4 here http://cr4.globalspec.com/thread/84531

Floats are easy if power were available. OP did not specify how far away horizontally the pump was located but wiring was not an option. A mechanical float system would work if it were tied to a pressure switch. The floats would likely resemble something like the float system found in the back of toilet reservoirs. When the tank is full pressure would be exerted on the water line to be detected by the switch on the pump and then shut the pump off. Conversely as the reservoir drops a few inches so does the float and opens the valve, as the pressure drops and the pump comes on to refill the reservoir. It is a little sloppy as a rugged system but somewhat easier than running up the hill to look in the reservoir.

A previous post suggested wireless activation and there are wireless floats. OP needs to search the web as I am too long removed from active work and retired. But my instrumentation guys a few years ago were installing infra red signals and wireless from wells to reservoirs. I know we used Greyline systems but have no longer a contact. I liked your answer but it required some clarification.

There is a third solution and that would be to use a continuous duty pump with water circulated back to the source well or source. The reservoir would be full at all times or at least to the limit of the pump v usage.

Wireless control with low power requirement has become affordable in recent years - maybe you could power the tank end with a small solar panel and battery. Your idea might work if your pump has enough excess head at low flow. Perhaps you could install a small pneumatic tank near the pump with a switch to turn off at high pressure and turn back on at a lower pressure. You might need a safe-guard to prevent cycling the motor excessively.

Your plan to control the pump bases on pressure can be made to work.

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You might not need the floatvalve, but it would allow use of pressure sensor/switch that isn't very precise. Adjustment wouldalso be easier.

. You don't want the pump to be cycling a lot, so placement of the sensor and selection of float valve is important.

Electrodes can also be used. You don't need to send the power all the way up and down the 70m , controllers working on a signal are readily available , for example used with borehole pumps.

What is the distance (height) between low and high level in your 100m3 tank?

I understand you do not want to run electrical or pneumatic connections from the pump to the tank? With float switches in the tank, you will need to run something.

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What is the diameter of the pipe from the pump to the tank and the capacity of the pump?

Does the pump always get the water on the suction side from a stable level?

Idea 1:

If you have enough height difference, stopping the pump could be done by measuring the current and compare to a set point. A timed delay has to be incorporated because the start up current will otherwise immediately stop the pump. You will also need a low pressure switch to restart the pump at low level.

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Idea 2:

You can also use a differential pressure device in a damper circuit where you adjust the hysteresis with a valve. Here you do not have to run wires or tubing to the tank. It is important to adjust the "full" tank position right.

There has to be a hold (OFF)contact, that can only be interrupted (closed) by the low level set point switch. You can find differential pressure sensors with enough precision for this purpose. The higher the tank us, the more accurate it will work.

You may consider using a laser pointer, which is switched on by a float switch in the low level position. Point the beam to a phototransistor at the pump to switch it on. When the beam is switched off at the high position the pump goes off.

Since you have NO electrical power at the storage tank, what you need is a hydraulically operated (via an adjustable pilot valve) altitude level control valve as manufactured by Ross Valve Co., of Troy, New York (USA)

You do not state what size pump discharge pipe you have. Warning, these valves, which are a specifically designed globe-type valve are NOT cheap. I've specified many of these valves over the years for elevated and ground storage tank level control. You can even have one manufactured with solenoid relays to control the pump operations.

No electrical supply near to the header tank. But can't you use an electrical line to connect a float switch in the tank? Normally a fixed telephone-type parallel line is used for this purpose, it should be fed with 24 V (ac) or less for safety reasons. This allows simpler maintenance than using wireless solutions. Pressure feedback solutions can be tricky. The parallel line is not copper so it does not attract thieves so easily. Guess the Vandals are not in Andalusia anymore.

brgds

Snel

Other than the great answers thus far using float switches, you could install a level transmitter (loop powered), install a relatively small solar panel (good outcome in Spain if you live not so mainly in the plain), and a battery bank to store energy for night-time and cloudy operation (just in case), and you even could wirelessly transmit the output of the transmitter to the pump controller, and then you have a cadillac system.

I have two solutions for you fully tested.

1) Have two floats wired in series specially designed for lower and upper limit and run a 100m cable down to the pump room to the controller / display unit for monitoring and control.

2) Have a capacitive sensor in the tank which I have tested for up to 6m depth of the tank and run two wire cable up to 100m to the pump room to have a water level on display meter. We have a very linear reading for water level from our sensor and similar one you may find in the market also.

As this work is often for professionals, My advise is that you call for help and get the sensor and controller installed. You also need to know the way system will work with your pump system.

Many thanks for all the great answers received. I think the most practical solution will be to use a mechanical level control device in the tank, either a robust float and ball cock or, the pilot operated isolation valve - not sure if this would work on such a small level change (3m) in the tank? Hopefully we can find a sensitive enough pressure cut out for the pump and timed delay for re-start. With normal usage the pump is started once very two or three days to refill the tank. Unfortunately, the solar and other sophisticated solutions around the tank will not work here as likely to be stolen. Here is an update of details of the current configuration: 1. Tank depth is 3m and capacity is approximately 220 cubic metres. I need to check at what height the feed pipe enters the top deposit and whether this impacts on the options. 2. Using Google Earth the lower deposit is at 53M and the higher deposit is 156M, so a difference of 103M. The total length of the pipe is circa 1.5KM. 3. The diameter of the upward pipe starts at 90mm and then goes to 75mm and not sure whether it then stays at 75mm to the top. I need to check by looking at the pipe into the top deposit as it is visible above ground. 4. The pump is fitted next to a tank at the lower level which is supplied from the main supply for the town. So fairly reliable but I need to check if the pump is fitted with a low level cut out.