Activating a pump based on water flow

[Paulo Borges]

Hi, I need to activate a pump to increase water pressure and would like to use a low cost solution.
I have a pump and I would like to switch it on when there is water flowing.
Once the initial water flux is very low I ordered a water flux meter like this:
https://tse1.mm.bing.net/th?id=OIP.VhTIypYjht52BIUlqKyXsgEsCp&pid=15.1&P=0&w=300&h=300

It is very sensitive and generates pulses as the water goes through it.
Then I need, from those pulses to activate a relay.
As long as there are pulses the relay must remain closed.
No pulses, relay open.

I started trying to use a circuit based on the 555 where a short duration positive pulse generates a pulse on pin 3 that I can control how long it remains active.

So, I thought that as long as new pulses where been fed on pin 2, pin 3 would never go down.

But it is not working like this, pin 3 pulses as well and I read a second pulse on pin 2 does not reset the counter of the timer and pin 3 will inevitably go down and be reactivated on the next pulse on pin 2.

Is there any way I can force the 555 to reset and keep pin 3 on as long as there are pulses on pin 2?

Thanks

 

[AnalogKid]

Yes. What you want is called a retriggerable monostable, or missing-pulse detector. As long as pulses happen often enough, the output is in one state. When pulses stop for a minimum period (the detection window), the output goes to the other state. This is the circuit that takes fan tach pulses and turns them into a running/failed signal. I can't do schematics right now, but I'll try to find an example.

What power is available to run the circuit?
What is the amplitude of the sensor pulses?
Sensor link / datasheet?
Does the circuit output drive the pump directly, or can it be a low-level control signal?

Your circuit has a basic error. Here is a 555 circuit that should be a starting point:

ak

 

[Paulo Borges]

Dear AnalogKid, thanks for clarification.
Sensor link: http://wiki.seeed.cc/G3-4_Water_Flow_sensor/
I have a 12vdc power supply and intend to activate a 12v relay to activate the AC pump.
The circuit I sent is a model I found online and was using it as a guide.
Regards
Paulo

 

[Paulo Borges]

By the way, the sensor, as you will see, generates positive pulses.
Paulo

 

[AnalogKid]

I'm not a huge 555 fan, but its big fat output stage can drive small loads directly. Relay details?

ak

 

[Paulo Borges]

Just a 12volts relay I got on the local parts shop, there are no other specs except it can drive up to 10A load.
Paulo

 

[Externet]

...I would like to switch it on when there is water flowing...

Be aware of details...
To activate a pump when there is flow... When the pump is on, water flows and tells the pump to keep running ?
How will it shut off ? Only when demand faucet closes ?

Consider a pressure commanded pump, like
----> https://www.aliexpress.com/item/Hig...lgo_pvid=fd43de16-2f5a-46a8-9d3b-d0cc4bc71de7

 

[Paulo Borges]

My problem is as follows:
Water tank, 1000L just 50cm above washer machine.
Washer machine has an electrical water in valve that has some sort of spring.
The water pressure is not enough to properly open the valve when that washing machine enables it.
The water flux is too low and it causes the washer machine to take ages to do its job.
The idea is that as the washer machine enables the intake of water there will be a little flux that will then switch on the pump.
When the water level is achieved the washer machine will close the intake valve, flux is interrupted, pump goes off.

A pressure pump would do the job but I already have a normal pump and would like to be able to make use of it by adding the flux control circuit been discussed here.

Thanks
Paulo

 

[Externet]

OK, understood. The washing machine shuts down the flow when filled and that should stop the pump.
If your existing 'normal pump' does not stop on pressure, go ahead with the flow sensor.

Extra suggestion off topic: Remove the hose attached to the washer machine end and check for debris obstructing flow at its inlet strainer.
Also to let you know the washer machine inlet electrovalve is active only when filling. You have power mains at that solenoid valve to control an added relay for energizing your pump, and shutting it off also when full.

 

[AnalogKid]

Can you measure the resistance of the relay coil? Photo?

ak

 

[Paulo Borges]

Thanks for the tips,
The Washer machine is brand new and I even removed a little filter on the water inlet to see if it would make a difference.
Filter clean.
I have considered your idea of just connecting the pump in parallel with the valve control, I am sure it would solve the problem.
But it would render the product warranty invalid, I had to think in a solution that would be entirely external to the washer machine.
If the machine was mine I would still go with the above idea but it is not mine and the owner is not going to understand that I have to void his warranty to solve the water pressure problem.
Thanks for your contribution.
Paulo

 

[Paulo Borges]

Relay detail:
Image: https://http2.mlstatic.com/D_Q_NP_22448-MLB20229697324_012015-X.jpg
Resistance of the relay coil: 385K

Paulo

 

[AnalogKid]

Resistance of the relay coil: 385K

No way. Make sure you are metering the correct pins.

Also, what is *all* of the writing on top of the relay?

ak

 

[Bluejets]

One could buy a low pressure goyen valve. Used to be available exactly for your installation.

 

[Paulo Borges]

Dear Bluejets, I tried that but could not find a pressure sensor sensitive enough to be activated by the very low pressure created by the water tank at only some 50cm height, that is why I went to try a flow switch.
Thanks

 

[Paulo Borges]

Hi Ak, you are right, I did not notice the decimal point, it is 385ohms.
And the print on the relay is not precisely that, I took a picture from the internet, the one looking most similar.
But what is printed on top of the relay is precisely as follow:
JQC-3F (173)
DV12V 28VDC
10 A 125VAC
But the look is precisely as the picture I sent.
Thanks again
Paulo

 

[AnalogKid]

That confirms a 12 V coil. I was hoping for a coil wattage number.

Based on the sensor data and your application, can you estimate the frequency of the pulses out of the sensor?

ak

 

[Bluejets]

Dear Bluejets, I tried that but could not find a pressure sensor sensitive enough to be activated by the very low pressure created by the water tank at only some 50cm height, that is why I went to try a flow switch.
Thanks

Well thats what we used to fit to machines some 25 to 30 years ago exactly to overcome the low pressure inlet.

 

[Paulo Borges]

You can find my sensor's details at http://www.hobbytronics.co.uk/yf-s201-water-flow-meter
The initial rate will likely be low as the water goes into the washer machine pretty slowly.
But as the first pulse will activate the pump the additional pulses will only keep the pump running.
If one input pulse generates, say, a 1 second output pulse I think it will be OK.
Regards
Paulo

 

[AnalogKid]

Circuit in post #2.
Rt = 470K
Ct = 2.2 uF
2N2907 can be 2N3906 or 2N4403

A possible problem is that the sensor output can stop in either state when there is no flow. In that case we might have to AC-couple the sensor signal.

ak