Winterizing main drain on pool wall

[joeypools]

I own a very small pool company and am winterizing a pool with a main drain on the size of the wall in the shallow end. I did not want to drain below it as it is much lower than the returns.

The line has its own valve. Do you always follow the same procedures as air locking a main drain? Does the line being on the wall change the physics of an air lock? I ask because after I lock the line it bubbles a bit afterward (as if water is entering the line).

There's also not an easy way to load the line with antifreeze so I'm really betting on the air lock.

A test I always do when air-locking lines is I will open the valve let's say 10 min after the air lock. If a lot of pressurized air gets release upon opening the valve, I know the valve is fine and not leaking air via crack or bad o-ring. I do get air pressure when I unlock the valve on the side of the wall as it should.

Just wanted to see if anyone experienced this.

 

[Catanzaro]

Joeypools:

Welcome to the forum. This is no difference between this drain and a regular main drain in the deep end when it comes to winterizing the line. A friend of mine has a spillover spa that has a suction, just like a drain. We clear the line, then shut off the valve trapping the air as normal ("Air Lock"), and this is right around the same depth as what you are describing. There is no other way to do this. It has been 5 years since the purchase of the home and not one problem.

Some may suggest leaving everything open, but I would recommend against this. There is one pool company leaves the lines open and a pool nearby started leaking water at the spa piping (underground), probably due to damage caused by freezing water. I would not take any chances.

No need for antifreeze as it will probably mix with water, and being that it is heavier than water, the probability is that it will get back into the pool. The only other thing I can think of is if the cover can be removed easily, the drain can be plugged like a regular return, but this is probably too much work.

However, I do like how you test for air in the system. For me, I open the pump cover and listen to hear if any air is escaping, in addition place my ear on the shut off valve to determine if air is escaping. This year, the valve failed on the inside, and there was no air escaping on the outside. The valve was replaced by swapping out the valve body inside with a new one.

 

[Catanzaro]

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[joeypools]

What a detailed response. Much appreciated. Thank you so much. I'll sleep better this winter because of this. Thank you. Also, for anyone that wants a better understanding of the effectiveness of antifreeze and how pipe size can affect the possibility of a pipe cracking, check out this freeze test: https://www.youtube.com/watch?v=F-xh0NjrKUk - it is extremely informative and interesting. He tests all different ratios of water to antifreeze and with varying pipe size.