Location of off-line chlorinator input line and temperature sensors

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M

mark.bailey

Member
Apr 26, 2021
7
Clinton, NY
Pool Size
30000
Surface
Vinyl
I'm redoing my pad plumbing, adding a couple of features, and trying to improve the setup. I have an off-line chlorinator and I'm planning on putting in a little automation that requires a temperature sensor. Documentation for both of these indicates that the input to the off-line chlorinator and the temperature sensor should be placed between the pump and the filter. My question: why? It would seem that either or both of these could be placed after the filter (and before the heater) and would improve things. I don't really want unfiltered water entering the chlorinator (causes clogs), nor do I really want to plumb anything between the pump and the filter.

Does anyone know why this is the recommendation location? Would there be any problem with plumbing this after the filter instead of before it?

Thanks!
 
Welcome to TFP! Good to have you here :)

By offline chlorinator, do you mean a liquid chlorine injector?

When sensing pool temperature, it doesn't matter much where, other than being before the heater. Most of the time, pool temperature sensors are located on the suction line, i.e. before the pump.
 
What I mean by offline chlorinator is one that take trichlor tablets and has an input somewhere after the pump and an output after the heater.

Thanks for the info on the temp sensor. It seems like anywhere before the heater would be fine.
 
OK, gotcha.

Trichlor is acidic, and when the system is off, will gradually acidify the water that's static while the system is off. You don't want the acidic water diffusing low pH water into your heater core where it could erode the metal in the heater core, thus shortening its life, and also add metal ions into your pool water.

If it was mine, I'd put a check valve after the heater, and then do any plumbing that could cause acidification of the water, after that check valve.
 
In reality, the only safe way to operate a tablet chlorinator if you have a heater is that the pump should never be off when tablets are in the chlorinator.
 
I'm not sure how that is true. The chlorinator has a check valve preventing chlorinated water from returning into the input. If plumbed after a check valve after the heater, super chlorinated water from the chlorinator can back into the heater. I'm pretty sensitive to the impact of chlorine on the heat exchanger for the heater and I don't think there is any reasonable way for highly chlorinated water to enter the heater. What am I missing here?
 
Once the pump is off, all systems balance. The acid solution coming from the chlorinator can seep within the equipment system.

Again. Your choice. The safest is what I presented. Not necessarily the easiest.
The best of both worlds is to not have a tablet chlorinator. Use liquid chlorine or a SWCG.
 
I believe the point Marty is making is that a check valve seals best when there is pressure against it. In a pool system, the pressure goes to zero when the system is off. If the check valve is spring loaded as most pool check valves are, that helps, but the pressure between the seat ring in the check valve and the surface of the check valve is quite low. Of course you're also relying on the fixture and would be unaware if the seat ring in the check valve had failed to seal under low pressure conditions. There's also the possibility of contamination lodging between the seat ring and the check valve body. If you have a multi-port valve on the filter, debris flows through the system if set on "recirculate" and occasionally after backwash depending how good the filter's spider gasket is, and how well the cavities in the multi-port valve cleared out. Generally speaking, a pool quality check valve is considered adequate protection for a heater, but it's fair to say not perfect.
 

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mknauss said:
Once the pump is off, all systems balance. The acid solution coming from the chlorinator can seep within the equipment system.

Again. Your choice. The safest is what I presented. Not necessarily the easiest.
The best of both worlds is to not have a tablet chlorinator. Use liquid chlorine or a SWCG.
Click to expand...
needsajet said:
I believe the point Marty is making is that a check valve seals best when there is pressure against it. In a pool system, the pressure goes to zero when the system is off. If the check valve is spring loaded as most pool check valves are, that helps, but the pressure between the seat ring in the check valve and the surface of the check valve is quite low. Of course you're also relying on the fixture and would be unaware if the seat ring in the check valve had failed to seal under low pressure conditions. There's also the possibility of contamination lodging between the seat ring and the check valve body. If you have a multi-port valve on the filter, debris flows through the system if set on "recirculate" and occasionally after backwash depending how good the filter's spider gasket is, and how well the cavities in the multi-port valve cleared out. Generally speaking, a pool quality check valve is considered adequate protection for a heater, but it's fair to say not perfect.
Click to expand...
I see. Such seepage would be inherent in any active chlorination system unless you had a system with separate plumbing and pump. So, it seems this is pretty unavoidable. I appreciate the information. Being hyper-vigilant about super-chlorinated water coming in contact with the pool heater heat exchanger is something I had to quickly develop after I bought this house!
 
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