Hi everyone, so I have a really big problem. So I am making a drinks machine that uses 2 different types of pump, (peristaltic for the alcohol, and mini air pump for the mixer, both 12v). After the peristaltic ones are primed they work as expected. However the air pumps continue to pump liquid after the pump turns off, and "extra" time the liquid is flowing is variable so I cant just account for the excess liquid.
How would I solve this problem, i did try putting a small hole in the highest point of the tube, but it didnt work too well and obviously water leaks, which cant happen.
So help would be much appreciated.
Thanks in advance.
Dean.
"the air pumps continue to pump liquid"?????
"small hole in the highest point of the tube..."
What tube would that be?
Hi,
Why are the air pumps pumping liquid?
When you turn the pump OFF, does the pump immediately STOP and it just remaining pressure that make the liquid flow?
Can you please post a diagram of the pumps setup?
Tom... 
Sorry I should have been more clear to everyone, the air pump, pumps air into a bottle that had two holes, one where the air pump comes in and one where the liquid goes out.
@TomGeorge yes you are correct about the pressure that keeps the liquid pumping, after the pump stops
So ... you can't use an air pump.
Unless perhaps you also include a normally open air valve to immediately release the pressure.
Even without the air pressure problem, the liquid has inertia and will keep flowing at zero air pressure. You have to have a vacuum for a short time to stop the flow.
Paul
What so would it be like have a 3rd hole in the lid and then when the pump stops also open the valve?
I used a uxcell Miniature Solenoid Valve 2 Way Normally Closed DC5V 0.22A Water Air Solenoid Valve to solve my leaky/backflow/siphon issue.
I use motor power for the valves to open them up.
What do you mean by motor power to open the valves?, just that you use the same voltage lines that your motors do?
Yes! Yes! Yes!
And does it need to be two way, i thought it would just need to be closed while the pump is on and open when the pump is off?
@Idahowalker
I do not understand the question.
With my use, a relay powers the motor and turns on the valve. The valve opens the pump pumps water, the motor stops the valve closes. The closed valve prevents back flow.
Hopefully, I have provided you with some info. The info may give you ideas on directions and hardware available that may help solve your problem. In your case you might have to do a bit of research to get the right valve for your requirements, I'm not going to do research for you.
But is it food grade? 
Again, this will be where the OP does his own research thingy on the thingy to get the thingy that does all the thingies that thingies need to do; including following the law thingies.
1 Like
Right ok, thank you all for your help, just 1 last question. I have 5v relays, that dc+ is to 5v and com to 12v. So do I need a 5v solenoid or a 12v solenoid. And can I run them on the same relay that I am using for the pumps.
Thanks in advance.
Dean.
This is never going to be great as the measurements will vary depending on the head of liquid/air gap .
Why not another peristaltic pump or a solenoid valve near the dispensing point .
That basically makes no sense. 
After a few beers, who cares?
I thought this was for mixed drinks?
Sterilization is a natural part of the process