Acid injector for pool - help needed


I have a new plaster pool and they use lots of acid for the first year or so. I've plumbed a line from the inlet side of my pump to a tank with 3 parts water, 1 part acid. I'm using irrigation drippers in line to regulate the flow and have it just right so it keeps the pool pH level correct. I know of other people who have done this and it works long term.
My problem is that when the pump shuts off, a small amount of the acid still siphons into the pool plumbing. Maybe because the tank is slightly higher than the pool level? Its about a quart over night.
I was thinking maybe a small spring loaded check valve would help, where just the spring pressure would be enough to stop the siphon flow, but when the pump is on and creates a vacuum, it would be enough to move the spring. Any ideas?
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On Oct 14, 9:29 am, snipped-for-privacy@gate.net wrote:

I've seen small check valves for fuel systems and they run pretty low pressure so the spring can't be all that big. But it will be an experiment to see if the pump vacuum is enough to overcome any spring. Got a vacuum meter you can put on the inlet? That would at least tell you the draw.
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There are systems available to inject chlorine for pools that work in the way you want. I'd find some of those online, check out how they are made, etc. You may get an idea or find a replacement part for one that you could buy and use. Those parts are at least chlorine resistant, so likely they would stand up to acid too.
But you definitely need something because you don't want the concentrated acid going into the pool pump and other system components.
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snipped-for-privacy@gate.net wrote:

You could use a venturi, like the ones used on ozone systems for spas, on the output side of the pump system, so that it will suck in the acid when the pump is running. This, and a check valve between the pump and the venturi will keep the acid out of the pump and filter. This would be similar to the installation of a chlorinator on a spa.
They make check valves for use in ozonator lines to keep water out of the ozonator. You can also buy tiny check valves at aquarium stores. Finding one that is acid resistant may be a problem.
A spring check valve with a metal spring will have problems with the acid. One aquarium check valve I've used has a rubber internal valve that might close tight enough. It's clear plastic, so you could visually inspect it for deterioration.
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On Wed, 14 Oct 2009 06:29:51 -0700 (PDT), snipped-for-privacy@gate.net wrote:

I think it is better to test and add based on your test. Too much acid is as bad as not enough.
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