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.

Step 1: Parts layout and parts list.

This project can be sized to fit the project you are working on so there is nothing special about 1" PVC.

Parts List:

PVC threaded adapter 
PVC threaded cap
PVC elbow
Plastic ( had nylon on hand) dowel with a diameter almost the same size as the inside of the size PVC that you choose
Some lead weight
high power magnets that will fit in the hole that you will drill in the plastic dowel
a rubber O-ring to fit the size of your dowel (see later steps)
A reed switch
Other PVC fittings and pipe to fit the application that you have
PVC cleaner
PVC glue

tools list:
Hacksaw or PVC cutter
A lathe or access to one is a real help.
27/64"  (for the 1" PVC size)
1/2" - 13 Thread per inch tap and wrench (also for the 1" PVC size)

<p>EricW76 I agree with your assessment. Matter of fact I have disabled the switch and am running the UV light 100% of the time. I thought that the flow switch design may inspire others to use it for other purposes so I left it listed. I have tried to delete this instructable so others may not go down my road but some how it is entered into a contest and will not allow me to delete it. When the contest is over I will try again.</p>
<p>This is an inventive design. But, turning off a UV lamp and back on will have two problems. One - bulb life is negatively impacted by number of power cycles. Two - and this is much more important - the UV bulb takes significant time to &quot;warm up&quot; when first turned on in order to provide adequate intensity to sterilize the water. The light wavelengths that actually sterilize bacteria is ultraviolet (you cannot see it with the naked eye). For the bulb to provide the necessary intensity, it can take several minutes to warm, depending on the bulb, and the age of the bulb. &quot;Glowing&quot; does not equal UV light. During that time, bacteria laden water will be flowing through your system and into your water system. This is why fluorescent UV systems typically are constant on. There are LED technologies that are coming that will offer that instant on ability you would need to safely do this. But cycling the bulb in fact does not provide safe water, and is not recommended.</p>
<p>Nice work... simple yet very useful....<br>Thanks for sharing<br>Voted</p>
<p>Nice! I've seen a bunch of hacks for water flow sensors and I'd say this is the best of the lot.</p>
With this setup, I would a little before getting a glass.
<p>I like the flow switch, what prevents the bacteria from migrating from the &quot;dirty&quot; side to the &quot;clean&quot; side withe the UV light off?</p>
<p>Good question. The UV chamber is about 36&quot; 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. </p>
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.
<p>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.</p>
<p>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?</p>
<p>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.</p>
<p>ok thanks, makes sense</p>
<p>Very clever! To see the problem, and to fix it.</p>
<p>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.</p>

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