Should eliminate main drain when installing new liner?

alosito

Well-known member
Jun 24, 2019
127
Simi Valley, CA
I am in contract to replace my vynil liner. The owner of the company that does the replacement suggests to cap the main drain. His arguments are:
- eliminate ten screws in the liner;
- eliminate potential leaks;
- eliminate the risk of someone drowning in the case where hair gets sucked in by the main drain.

He is also saying that in order prolong the life of the liner by almost 100% I should keep the pump running 24 hours a day. And if do that, the circulation is going to be good enough anyway without the main drain. Considering that I am in California and I never drain my pool, what he says sounds convincing. What do you think? Should I cap the main drain when installing a new liner? This is all I am going to have left to provide circulation (one skimmer and three jets):

IMG_4693.jpg
 

ajw22

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Jul 21, 2013
40,102
Northern NJ
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I would not cap a main drain with one skimmer if your main drain can actually pull water. Even though folks will say the pool will run fine.

How is your main drain connected to the pump?

A main drain that is operating properly will prevent the pump from running dry should the water level drop below the skimmer mouth.

Many main drains don’t work properly and then closing it does not matter.

How deep is your pool at the main drain?
 

mas985

TFP Expert
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May 3, 2007
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Pleasanton, CA
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I would agree with most of what he said. MDs are not really required and you really don't need much in the way of "extra" circulation without one. They really don't do much and you really shouldn't drain a pool via the MD anyway as the pump will likely lose suction before all the water is gone anyway.

Where I disagree is that you need to run 24/7 for circulation without a MD. Right now, I am running 3 hours per day and I don't draw much from my MD. The circulation added by a MD is insignificant. Also, I am not sure about the claim that the liner will last longer. I can't think of a reason why that would be true.

Allen does have a point about equalization. However, my experience is that the equalizers in skimmers don't really help that much unless you are running at very low speeds. Once, I had to repair the grout in one of my skimmers and so lowered the water level below the skimmers. I couldn't run the pump more than about 1000 RPM before the skimmer would start to suck air even when I used a skimmer float that is supposed to seal the skimmer bottom. They really don't seal that well (tried pool lube too). The MD/equalizer port is primarily gravity fed into the skimmer so the flow rate into the skimmer bucket from the MD is somewhat limited, especially at low pool levels, and if the pump runs at higher flow rates, the skimmer port will start to suck air. But it probably depends on the type of skimmer you have and the equalization valves it might be using.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
40,102
Northern NJ
Pool Size
35000
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Plaster
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Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Even if air is being drawn in when the skimmer water level is low and the water is coming from the main drain the pump should get enough water flow to prevent it running dry and damaging the seal.
 

mas985

TFP Expert
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May 3, 2007
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Pleasanton, CA
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My experience is that once the skimmer port starts sucking air, the pump loses prime and then no water flows into the pump. However, even at that point, the pump should shut down on it's own since it is a VS pump and that particular model shuts down when it can't prime or detects a clog (i.e. no flow rate).
 

Jimrahbe

Mod Squad
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Jul 7, 2014
28,155
Bedford, TX
A,

You do not need a main drain and your pool will work just fine. I have two rent house pools that do not have operating main drains. The idea that your pump could run dry, is technically true, but would mean you only look at your pool once a month? When in the life of your pool have you allowed the water to drop below the mouth of the skimmer? My two rent house pools are in total are almost 20 years old and they have never run dry.

I do run my pumps 24/7, but I don't do that for circulation, I do it because I have a SWCG and I like to generate a little chlorine all the time. Shutting off your main drain will have zero effect on your circulation.

Thanks,

Jim R.
 
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mas985

TFP Expert
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May 3, 2007
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Pleasanton, CA
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His argument is that when you don't run the pump 24/7, pool chemical accumulate on the bottom of the pool and harm the liner.
If the chemicals are added to the pool properly, that should never happen. Once dissolved in the water, they should remain suspended even when the water is idle for long periods of time.

But since you have a VS, as Jim pointed out, you can run them on very low speeds 24/7 if you want to.
 

mas985

TFP Expert
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May 3, 2007
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Pleasanton, CA
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BTW, how do you chlorinate your pool? If you are using granulated chlorine, then that can sink to the bottom before dissolving. Same with dry acid. Neither of these we recommend using, especially in a vinyl pool. And I still wouldn't use them even if the pump is running 24/7.
 

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