Picture of How to make a flow switch
First let me say that this is the very first Instructable that I have made so please be easy on your critiques.

I have a very elaborate well water treatment system that had been plagued with problems.  One problem is I am using chlorine to kill bacteria and then removing the chlorine with charcoal before the water gets to my RO membrane.  Anyway that is more than enough background.

I decided to eliminate the chlorine and install a whole house UV filter.  The UV bulbs are good for 9000 hours and most people, I assume, just plug them in and leave them.  I fail to see any benefit to the light being on when there is no water movement so I figured I would control the light with a flow switch.  All of the flow meters that I found on ebay, Amazon or Grainger were either too expensive or did not give me the specifications that I was looking for.  So its do-it-yourself time.

The object of this project is to detect the movement of water in a 1" PVC pipe and turn a receptacle on and off. 

This is the finished project.  Most of the PVC was just stuff found in the workshop so please ignore the stains.
amorarun1 year ago

Nice work... simple yet very useful....
Thanks for sharing

etcmn1 year ago

Nice! I've seen a bunch of hacks for water flow sensors and I'd say this is the best of the lot.

muddog151 year ago
With this setup, I would a little before getting a glass.

I like the flow switch, what prevents the bacteria from migrating from the "dirty" side to the "clean" side withe the UV light off?

radarguy (author)  Dprovenzano1 year ago

Good question. The UV chamber is about 36" long and fortunately for us bacteria have very very short legs. I guess if you left the system go stagnant for a long time that might be a problem but my system gets used at least every couple of hours.

johng6521 year ago
Have you thought of incorporating a redundancy switch powered by the pump circuit? Pump turns on flow circuit must turn on, or alarm sounds and the pump turns off. This keeps your system free of bacteria downstream of the light. Those reed switches are only rated for so many cycles, and are notorious for failing at the most critical times.
radarguy (author)  johng6521 year ago

The problem with the pump switch is that the pump maintains pressure in a tank that has a bladder in it. Once the tank and system are up to pressure and the pump turns off, any demand for water is satisfied by the air in the bladder until it reaches the bottom of the hysteresis curve and turns the pump back on for the next cycle. All that while the bladder is moving water past the UV filter and it won't be on because the pump is not on. Which defeats the purpose of the UV filter.

diy_bloke1 year ago

very smart. was just wondering if you dont need a certain amount of flow to push up the weights, or in other words, can the water flow slowly without activating the switch?

radarguy (author)  diy_bloke1 year ago

In my mind the pump and system has 40 to 60 PSI on it all the time. When the demand calls for the pump to come on there is a lot of volume of water moving through the system and in order to pass the switch it has to get the capsule out of the way in order to get to the output. In my research I have found commercially available switches that use this principal except that they use a spring instead of gravity. I wanted the least amount of friction and the most sensitivity so I made the tolerance close and buoyancy just a little negative. O' boy I did not talk about the buoyancy, did I? I hope I can edit it.

ok thanks, makes sense

rimar20001 year ago

Very clever! To see the problem, and to fix it.

Thanks for posting this ! I'm going to be installing a similar system at my cabin in the next couple of years. I was planning on using the auto pressure switch on the pump to turn on the UV light, but if that doesn't work out you've given me an option.