chlorine off-gassing in peristaltic pump supply lines

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R

rcrovo1

0
Jun 4, 2014
5
lexington ky
Hey guys,

I have searched on this topic and haven't found a answer as to how to fix/live with it so hopefully you can give some more info. I have installed a rola chem 12gpd pump with 15 gallon tank. I have only had it up and running about a week. When I first installed it I placed it on the equipment pad outside where it gets afternoon sun. I found that the 10% bleach was off gassing in the clear nylon lines causing bubbles in the lines. eventually it would off gas so much that there would be a large portion of the line without liquid and if left alone I assume the entire line would be without any liquid and would run dry. I didn't like having the chlorine exposed to the sun especially with the clear lines and found that the off gassing was worse as the solution got warmer, so I elected to move the pump and chlorine tank inside (luckily the equipment pad shares an exterior wall with my garage). So the tank and the pump are currently mounted inside the garage and the feed line runs through a small hole in the wall outside to the port in the return side of plumbing. outside I have sleeved the clear nylon tubing with an opaque tubing to shield it from he sun. after moving the pump/tank inside it is in shade all day and has reduced the amount of off gassing considerably. however, after a few days all the small bubbles find their way to the highest point which is the pump and sit there. basically, it has just reduced the amount of off gassing so it will take longer for the tubing to fill with air but hasn't fixed the problem. so, my questions :

is there any way to prevent this from happening?
will this cause a problem if left alone?
if the bubbles get injected into the pool will they still be sanitizing? (are these bubbles chlorine gas or is it just air?)
what can be done to improve the performance of this system?
appears that stenners come with black tubing so perhaps there are bubbles in these lines as well that users are just unaware of?


Thanks in advance!
 
Are you using straight bleach without dilution? The more you dilute chlorine the more resistant it is to heat. I would dilute at least 4:1. You may have to fill more often but my guess is that you are wasting a lot of chlorine so refill rates may be much less than 4:1. I am sure that even the garage gets pretty hot. Also, the injection rate will need to be increased which might help with the build up of gas.
 
thanks for the reply...I failed to mention that when I moved the system into the garage I also diluted the chlorine. I nearly cut it in half. should be close to 5-6% now. I could cut it further and see if that improves the off gassing and then as mentioned above increase the output of the pump.
 
I would cut it again and see if that helps. But no matter what liquid is involved, even just water, as it heats up it will still out gas some.
 
Rather than diluting the bleach, I would suggest you simply use a lower strength form of bleach, perhaps try to find 6% bleach if you can. The reason being is that bleach is rather sensitive to pH. Normally a bottle of bleach has excess lye in it which keeps the pH above 11.5. When you cut the bleach strength in half using tap or distilled water, the pH of the resulting solution is lower. The stability (rate of auto-oxidation of bleach to oxygen gas and chloride) versus pH curve is fairly steep when you get outside the normal pH range of the manufactured product and so you could actually be causing more problems by diluting it.

As for what the gas bubbles are, they are likely oxygen gas caused by the breakdown of bleach. Are you sure the tubing you are using is compatible with concentrated bleach solutions and capable of withstanding high pH? That could be contributing to the breakdown of the bleach and the formation of gas in the line.
 
I'm with JoyfulNoise here...
I use 12.5% bleach ... well, it is made at 15%, and sold as 12.5%.
I have a 55gallon drum of it that I buried beside the equipment pad to keep it cooler than ambient temperatures, and I have not noticed ANY out-gassing in the tubing from the higher chlorine level.
The Stenner tubing is rather cheap, and it is rated for higher concentrations of chemicals than those that we use. If it will work with your pump, I would give it a try.
 
Thanks guys, ill price the lower concentration and see. I am using 10% (cut with water right now) because it was on sale. Also, since I teach scuba in my pool I have convinced the local distributor that I am a commercial pool and they agreed to sell me the 12.5% that all the local public pools use for $2.50/gal. I would hate to have to pass on that deal!

As far as the tubing goes it is standard clear nylon that came with the pump. The owners manual states that it is approved for use with up to 12.5% bleach. If it wasn't clear I would not even know that there where bubbles in it. RonsPlc is your tubing clear or opaque? If it is clear and you have no bubbles then perhaps you are on to something with the tubing. If it is opaque do you have a way to know that there is no bubbles in it? Ill have to check on that stenner tubing as well.

thanks
 
The tubing I am using is clear enough that I can see bubbles in it (if there are any), but it isn't see through clear.
Next year, I am going to get some of the UV black tubing, as the pump, and barrel are outside. This is my first year with the pump, and I am VERY pleased with it.
 
Since this is a peristaltic pump and is self priming would adding a couple of minutes to the run time solve the problem? Unless your lines are extremely long all the air should be gone in a few minutes.
 
JoyfulNoise said:
The stability (rate of auto-oxidation of bleach to oxygen gas and chloride) versus pH curve is fairly steep when you get outside the normal pH range of the manufactured product and so you could actually be causing more problems by diluting it.
Click to expand...
If that were an issue, wouldn't people that use the liquidator and other diluted dosing systems have mentioned that?

Homemade Acid OR Chlorine Injection System
 

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mas985 said:
If that were an issue, wouldn't people that use the liquidator and other diluted dosing systems have mentioned that?

Homemade Acid OR Chlorine Injection System
Click to expand...

I believe the saving grace for the Liquidator is that the concentrated bleach solution sits at the bottom of the tank as a separated layer from the water above it. So the pH change in the actual bleach volume is much smaller. Also, the water above the bleach layer in the LQ is pool water with CYA in it so there is some small degree of stabilization to the chlorine in that layer. I suspect the bleach in the LQ probably does degrade faster as compared to bleach in a bottle but it is not nearly as much as when you actively mix bleach and water to reduce concentration.

There are several scholarly papers online about bleach stability versus pH. The primary degradation pathway is hypochlorite degrading into chlorates. That has the greatest rate constant. The secondary pathway is hypochlorite degrading into oxygen. That has a lower rate constant. But, if one adds divalent metal contaminants to the bleach (transition metal impurities such as Fe2+ or Cu2+), then the secondary pathway of oxygen degradation increases quite a bit. It also turns out that bleach with higher salt concentration is more stable than bleach with lower excess salt. Therefore both pH and salinity affect bleach stability which makes dilution tricky.
 
What kind of degradation rates are we talking about? If you fill a container once a week or every two weeks with a 4:1 solution, how much would be lost during that period of time?
 
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