How does a trichlor chlorinator work?

I have an inground plaster pool, currently chlorinated by floating ducks, and would like to install an automatic chlorinator - an "off-line" chlorinator that connects to the main pool lines through 1/4" plastic tubing. Trichlor tablets.
The pool pump is powered down at night, and I need to figure out what will happen with the chlorinator when the power is off - whether the chlorine concentrate will flow back into the pump. But what I can't find is a diagram or description of how these chlorinators actually work.
If I were designing one, I think I would have a container with a sealed lid at the top for adding the trichlor pucks. Then I would have an inlet at the very bottom, and the outlet connected to a standpipe. With the container being sealed, the incoming water would rise to just above the level of the standpipe opening, and the trapped air would keep it from going higher.
Is that how they work, or is it different?
So when the pump is shut down, does the water inside the chlorinator just stay put, or does it tend to flow one way or the other?
And does anyone have a particular brand they like?
Thanks for any insights.
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I suggest posting here:
http://www.poolspaforum.com
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Chlorine does a real number on these things and the in-line variety aren't cheap.
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On Sat, 07 Apr 2012 12:20:45 -0500, Peabody

I've got one on my pool. It's a cylinder about 2.5 feet high including base. It's got a connection in the middle of the bottom and another one a couple inches up on the side. The water just goes in one of those and out the other so that it eats up the tablets in the bottom first. It will hold about 10 tables. The side connection has a little valve that you can use to adjust the flow. The bottom valve has a check valve built into it, presumably to prevent the concentrated chlorine water from getting into something. In the past I've had the check ball get stuck and have just drilled it out and it never seemed to cause any problems, I ran it for years that way. The thing is over twenty years old and all I've had to do is replace the plastic lines that go to and from it a few times as well as the valve and connectors a few times. I replaced the O-ring in the top screw on cap once. I prefer it to putting tabs in the skimmers as it seems easier to control the dosage.
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Ashton Crusher says...
> I've got one on my pool. It's a cylinder about 2.5 feet > high including base. It's got a connection in the > middle of the bottom and another one a couple inches up > on the side. The water just goes in one of those and > out the other so that it eats up the tablets in the > bottom first. It will hold about 10 tables. The side > connection has a little valve that you can use to adjust > the flow. The bottom valve has a check valve built into > it, presumably to prevent the concentrated chlorine > water from getting into something. In the past I've had > the check ball get stuck and have just drilled it out > and it never seemed to cause any problems, I ran it for > years that way. The thing is over twenty years old and > all I've had to do is replace the plastic lines that go > to and from it a few times as well as the valve and > connectors a few times. I replaced the O-ring in the top > screw on cap once. I prefer it to putting tabs in the > skimmers as it seems easier to control the dosage.
Thanks very much, Ashton. So I assume the bottom port with the check valve is the input port. Is that right? That would be the line that connects between the pump and the filter.
Also, do you run your pump 24 hours, or shut it down at night?
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