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.

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 Tee
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)

The capsule is the moving part that will signal the reed switch to turn on the UV light.
I helps greatly to have a lathe otherwise you are left to your own creativity.

For the 1" size PVC I made my capsule approximately 6" long.   Turn Its diameter of an 8" length to 1/16" smaller than
the nominal inside diameter of 1" PVC pipe.  Cut off 3"  and drill a 27/64" hole in the 5" section to withing 1" of the bottom. (I accidentally drilled too far and that is why there is an epoxy joint at the bottom)  This also happens to be a good size the 
magnets will fit in.

Next, tap the hole about an inch deep.  It is easier to do this while it is in the lathe chuck.

Now put the 3" piece in the lathe, trim about 1/2" length down to 1/2" diameter and cut a thread all the way.  If you don't know how to to do this then you may need to seek some help.  A die of the right style might work but it needs to be full threads all the way to the hilt and the hilt needs to be square.  

Trim the top of the capsule to about 1 - 1/2" and round the ends of the top and bottom so it won't hang up when doing its job.

While you are at the lathe take the threaded adapter   (the part screwed into the cap at the top above the capsule)  and increase the inside diameter to the same diameter as the PVC pipe.  This will allow you to service the capsule should you need to.

Now take the 5" and drop in the lead weight.  I put a spring in next but almost anything will do to keep the magnets as close to the top of the hole as you can without interfering with the threads.  Then drop in the magnets.  I used just 4 after experimenting with the capsule inside a test piece of PVC so that it would activate the reed switch.

Next put a 1/2" inside diameter O-ring over the threads of the top and screw it on tight enough to compress the O-ring about half way. You don't have to kill it!

TESTING:
Now the capsule is complete and it is time to calibrate it.  It must be negatively buoyant.  That means that it must sink in the water or what ever fluid you will be using.   So with it tightened put it in a container of water and make sure that it sinks.  Depending on the viscosity, flow and the sensitivity that you want this can be adjusted by adding or removing weight.  Now you are ready to assemble the whole switch.

OPTION:
With a little redesign you could use a spring instead of gravity like I did to return the capsule to the off position.

Lay all of the fittings out with the capsule so that you can measure how long the two pieces of 1" PVC need to be.  They can actually be longer than need but they cannot be too short.   Put the capsule below the Tee so that the top of the capsule is about even with the bottom of the left going hole in the Tee.  See the picture.  Now measure for the lower length of PVC.

The upper length of PVC need to be long enough so that when the water flows (from the bottom)  the capsule has plenty of room to get out of the way. 

Once the pieces are cut put them all together like the drawing.  Make sure to use teflon tape or goop on the threaded cap.

You are now read to install it.  In my case you can see the shinny housing of the UV lamp housing.  Also notice the position of the reed switch.

I used a reed switch from an old window burglar alarm but you may have something different.  They do make them to take 120 volts AC but I chose to just use what I had which is good for maybe 5 to 12 volts with low current.  So with that I need to make an adapter box.  Simple enough circuit so I won't bore you with that. 

I also had a 12 volt DC controlled relay that can handle 120 volts AC.  So I used a 12 DC wall wart to control the relay through the reed switch which in turn powered a receptacle on the side of the box and a Hobbs meter on the front.  A Hobbs meter is a device that has a speedometer like display that just counts up the hours that what ever it is connected to is operating or powered up.  They are on things like generators, tractors, heavy equipment or anything that need maintenance by the hour.  Check ebay for some examples.  In my case I wanted to count up to 9000 hours so I know when to change out the bulb.  I had one on my hurricane generator which I have not used since 2004 so I just borrowed it.

The Position of the reed switch may need to be adjusted once you have water flowing so like I did have temporary wire holding it. Turns out it worked right off the bat without any adjustments.

Thanks for reading this far.  Let me know if you have any questions.  It was a pretty easy project and I have not seen anyone else tackle this problem.