Main drain blow out at closing

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shiyang100

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Jun 11, 2016
153
Boston, MA
I hired the same company doing the closing a few days ago. I have 2 skimmers, one MD, and 2 returns. The skimmer lines and MD lines piped individually to the front of pump. As usual, the tech blew through one of the 2 skimmers. and closed in the order of the other skimmer, 2 returns and the skimmer which was used for blow out. I was there all the time, but interestingly I couldn't remember seeing the air bubbles coming out from the MD.

Is that a big problem without blowing out the MD on the 9ft deep end in case the tech forgot? I am in MA, so the frost line is usually 2-4 ft. I searched the forum here. Some said blowing out MD is not necessary, while others said the other way. If I can, I don't want to bother the pool company coming out again taking off the cover and reblowing the line.
 
Shiyang:

If you paid a pool company to close your pool, then they will have to come back if the main drain was missed. Personally, I would not take any chances with the MD. You would not have missed the bubbling effect on the surface for the main drain. It is like a cup full of water and you blowing through a straw at the bottom and the top starts bubbling, but on a bigger scale.

If you watch some videos on line at You Tube, you will see the difference. This year, I am going to take some pictures of the process and link them to the thread and concept of a swimming pool, so it is easier to follow.
 
MD will not be an issue. Think of it this way, bottle left in freezer with cap off, the ice will just grow out the neck, place cap on and ice will break the bottle. Even if he blew the MD clear of water, there is no way to truly seal it. I have seen pressure plugs shoot out from a ball valve for two reasons, the inside of the union is smooth and the pressure of the water wanting to get back in the pipe is huge.
 
I performed a test 2 years in a row. 4 foot 3" schedule 40 PVC. One side sealed with primer and glue. The other side just a cap. The first year, the water was 90% full and no problems with any leaks for breaking of PVC. Left outside in the freezing cold and wind. The 2nd year, I fill up all the way 99.99% and placed cap on. The cap actually moved (as I marked it) about 3/4".

One would wonder if the MD can truly freeze and break the piping. The MD is deep, way under the freezing line. Also, the return jets (black plugs) would probably pop out.

In theory, nothing should happen, but I always recommend closing a pool properly. Just in case.
 
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