Water tank automatic refilling

Thread Starter

topbobster

Joined Jan 14, 2019
6
Hello, new to AAC so hello everyone....
I did a search on my topic of interest and whilst there were a number of threads about ways to complete, one way I had in mind didn't seem to be covered. I did pick up a few things within those threads that I hope will help me give all necessary detail:
The potable water tank is to be used to water veg at an allotment so no chance of AC power, it will be 12v DC.
I need to refil this tank from a larger tank that collects rainwater or filled from mains. Is it possible to set up a circuit with two stainless steel float valves (example linked below), one at the higher level and one at the lower level. When the lower level indicator drops it switches on the pump and when the upper indicator rises it turns off the pump.
The way I see it is the indicators can both be in either orientation and I see some sort of logic but I cannot fathom the correct components that will enable:
The lower indicator, when it goes into one state, to start the pump but then has no impact when the same indicator changes state again as the water rises - and then upper indicator stops the pump when it changes state (as the tank is full) but again has no impact as the water level lowers. Any help would be much appreciated.


(https://www.ebay.co.uk/itm/Stainles...m=122220622417&_trksid=p2047675.c100005.m1851)
 

dendad

Joined Feb 20, 2016
4,451
If you use a switch that has a folat cord running through the toggle arm, and a stopper to set the start and another the stop positions, that can switch the pump on and off.
The hysteresis is determined by the stoppers on the cord.
 

AlbertHall

Joined Jun 4, 2014
12,344
You need a bistable flip-flop. This has 'set' and 'reset' inputs and it's output would control your pump. While the lower switch is indicating low water level it will hold the bistable in the 'set' state. As the water level rises the bistable will hold that state. When the water reaches the upper switch that will operate the 'reset' input and turn off the pump. This state will then be held until the lower switch once again trips.

The bistable might comprise two transistors or it may be an IC (the CD4013 has two of them) or a latching relay.

To design the circuit some information will be required:
For both level switches is contact made or broken at the trip points?
How much current does the pump need?
 

oz93666

Joined Sep 7, 2010
739
You need a bistable flip-flop. This has 'set' and 'reset' inputs and it's output would control your pump. While the lower switch is indicating low water level it will hold the bistable in the 'set' state. As the water level rises the bistable will hold that state. When the water reaches the upper switch that will operate the 'reset' input and turn off the pump. This state will then be held until the lower switch once again trips.

The bistable might comprise two transistors or it may be an IC (the CD4013 has two of them) or a latching relay.

To design the circuit some information will be required:
For both level switches is contact made or broken at the trip points?
How much current does the pump need?
All totally unnecessary .... dendad is correct ...

You need just one of those float switches in your link ... positioned at the top water-level in your upper tank , as soon as the water level in this tank drops 1cm or more the switch is closed and your pump is turned on , when the water reaches max level again it switches off ... easy!
 

LesJones

Joined Jan 8, 2017
4,174
Those switches look like they woud be difficult to mount as they need to be mounted with the axis vertical. Switches such as this one could be mounted through holes in the side of the tank. I suggest using two of these both positioned so the contacts were open when submerged. I would use them together with a double pole single throw. (Or double throw.) The contacts on the lower switch would be in parallel with a set of normaly open contacts on the relay which connected the 12 volt supply across the relay coil. When the lower switch was not submerged it would latch the relay on. The upper set of float switch would be in series with the coil so that it would unlatch it when it became submerged. The second set of contacts on the relay would switch the pump on.

Les.
 

oz93666

Joined Sep 7, 2010
739
Those switches look like they woud be difficult to mount as they need to be mounted with the axis vertical. Switches such as this one could be mounted through holes in the side of the tank. I suggest using two of these both positioned so the contacts were open when submerged. I would use them together with a double pole single throw. (Or double throw.) The contacts on the lower switch would be in parallel with a set of normaly open contacts on the relay which connected the 12 volt supply across the relay coil. When the lower switch was not submerged it would latch the relay on. The upper set of float switch would be in series with the coil so that it would unlatch it when it became submerged. The second set of contacts on the relay would switch the pump on.

Les.
Your link goes to the same page as TS linked to ....

Certainly you have to decide weather the switch is to be side or top mounted , but only one switch is needed !!!

A trend by posters is to make things too complicated ...

One float switch! ... make sure it can switch the current of your pump , and make sure it switches on when level falls
 

KeithWalker

Joined Jul 10, 2017
3,063
Those switches look like they woud be difficult to mount as they need to be mounted with the axis vertical. Switches such as this one could be mounted through holes in the side of the tank. I suggest using two of these both positioned so the contacts were open when submerged. I would use them together with a double pole single throw. (Or double throw.) The contacts on the lower switch would be in parallel with a set of normaly open contacts on the relay which connected the 12 volt supply across the relay coil. When the lower switch was not submerged it would latch the relay on. The upper set of float switch would be in series with the coil so that it would unlatch it when it became submerged. The second set of contacts on the relay would switch the pump on.

Les.
Dendad's suggested solution is well tried and tested. It is very simple and reliable, as anyone who has a sump pump in their basement will testify.
 

drc_567

Joined Dec 29, 2008
1,156
if you allow the reservoir to completely drain to the extreme lower level, the useful water pressure at the hose end will be minimal. If you obtain a 10 foot section of 8 inch diameter PVC pipe, and use that to hold the water, you will have at least 5 psig, as long as the pipe is filled. The capacity of the 10 ft pipe will be approximately 23 gallons of water, and evaporation should not be excessive. A single float valve at the top of the pipe could be configured with a normally on relay, to turn the pump off as rising water activates the float switch and energizes the relay coil, opening the switch to the pump.
If it turns out that the pump is cycling on excessively, then use additional lengths of PVC pipe, connected with 2" pipe at the base to create a larger capacity reservoir. If you are using drip or slow release irrigation, the additional water pressure may be beneficial to your objective.
 

drc_567

Joined Dec 29, 2008
1,156
... add incremental weights to the top of the float. Then it would not rise and switch on until it was completely immersed in water. ... Has to be just right ... not too much, not too little.
 

Thread Starter

topbobster

Joined Jan 14, 2019
6
Thanks for all the replies so far...Let me clarify a couple of things...
Firstly please don't worry about mounting. I intend to fettle mounting with the aid of 3D printing/other (FDA approved water safe PLA). I 'had' no intention of putting holes into my tank - if you new how long it took me to build it outside in the 'English weather' in October, and the cost of fibreglass resin for potable water etc. you might agree...
The size of the tank is 1.2m long, 30cm wide, 25cm deep so approx 90 litres. My intention is to start refill at 11cm then stop at 22cm so that I have at least roughly half full tank if the main tank runs out. The fill pump to this one will have an override curcuit with a low level float valve in the main tank to stop the pump from starting if it's nearly empty. I will post some replies to those who have reponded...
 

Thread Starter

topbobster

Joined Jan 14, 2019
6
If you use a switch that has a folat cord running through the toggle arm, and a stopper to set the start and another the stop positions, that can switch the pump on and off.
The hysteresis is determined by the stoppers on the cord.
Wasn't sure I could picture this so held onto the idea as I read on...thanks DenDad
 

Thread Starter

topbobster

Joined Jan 14, 2019
6
You need a bistable flip-flop. This has 'set' and 'reset' inputs and it's output would control your pump. While the lower switch is indicating low water level it will hold the bistable in the 'set' state. As the water level rises the bistable will hold that state. When the water reaches the upper switch that will operate the 'reset' input and turn off the pump. This state will then be held until the lower switch once again trips.

The bistable might comprise two transistors or it may be an IC (the CD4013 has two of them) or a latching relay.

To design the circuit some information will be required:
For both level switches is contact made or broken at the trip points?
How much current does the pump need?
Bistable flip flop....jump forward to Latching relay - now you're talking...I researched and that's the kiddy I imagined...
For both level switches is contact made or broken at the trip points? Can be either because they can go in either way up. I could suss this out by trial and error to find which works.
How much current does the pump need? 5 or 6A
 

Thread Starter

topbobster

Joined Jan 14, 2019
6
All totally unnecessary .... dendad is correct ...

You need just one of those float switches in your link ... positioned at the top water-level in your upper tank , as soon as the water level in this tank drops 1cm or more the switch is closed and your pump is turned on , when the water reaches max level again it switches off ... easy!
Oz it would seem that you're suggesting the pump start filling when the upper level goes down by 1cm...no good for me; more detail given in my update above. Thanks for the response Oz
 

Thread Starter

topbobster

Joined Jan 14, 2019
6
Those switches look like they woud be difficult to mount as they need to be mounted with the axis vertical. Switches such as this one could be mounted through holes in the side of the tank. I suggest using two of these both positioned so the contacts were open when submerged. I would use them together with a double pole single throw. (Or double throw.) The contacts on the lower switch would be in parallel with a set of normaly open contacts on the relay which connected the 12 volt supply across the relay coil. When the lower switch was not submerged it would latch the relay on. The upper set of float switch would be in series with the coil so that it would unlatch it when it became submerged. The second set of contacts on the relay would switch the pump on.

Les.
Les, mounting menioned in my updated above. Your explanation of the wiring of the DPST was one thing I have wondered about but wasnt sure it was possible - nice to know for the future though - however I think the latching relay might work for me...Thansk for the info.
 

drc_567

Joined Dec 29, 2008
1,156
... You have a custom built tank, with a depth of 25 cm. At what height above ground is it mounted? You will find that you get approximately 0.4 psig or 3 kpa, per 30 cm of water elevation above the outlet at the hose end. Drip irrigation would not seem to require too much water pressure though.
 

Reloadron

Joined Jan 15, 2015
7,501
Not knowing the dimensions of your tank or the environment (anything around me right now is frozen) or your 12 VDC pump current you could think about something like as seen here. In the animation of the link the tank labeled sump would be the tank you are filling. The circuit would be all 12 VDC for your pump and is just a common latching relay circuit. The relay depends on the pump current for selection but it is juast a 12 VDC coil DPDT relay with contacts rated for your pumps DC current load. You may want to add a diode across the pump to act as a flyback diode.

Again it all depends on the environment, size of your tank, and pump current including the pump start current. Stainless float switches is what I would consider using.

Ron
 

oz93666

Joined Sep 7, 2010
739
.... except that there would be virtually zero hysteresis, so the pump would be cycling on and off rapidly.
Why would manufactures make a pump switch with virtually zero hysteresis??? It would be unusable ...

those switches in the links are designed for just this job .... I have used one and it works fine.
 
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