Please explain how this works: Purging main drain line

[rickmnj]

So, I did everything as advised on closing my 70's Anthony inground pool except dealing with the pools main drain line and the bottom/floor drain line of the attached "spa".

Of two skimmers, the one closest to the filter/pump etc has the two holes at the bottom, one for suction (filter) and one for the main drain. I disassembled my filter setup and vacuumed all the water from the suction line and plugged for the winter.
Now the skimmer has the main drain hole with water visible....as it should be.

Some tutorials recommend blowing out the main drain line from where the valves are situated near the filter/pump. When air bubbles out from the main drain then turn the valve to air lock the pipe. My question is: How can this be done if the main drain line ends at the bottom of my skimmer? Is my setup different than others?

The abovementioned question not withstanding, I was thinking I would either use a "foam rope" or utilize a plug with Schrader valve to purge the main drain line from the bottom of the skimmer.

Thoughts?

 

[X-PertPool]

You would blow out the maindrain at the hole in the skimmer and then quickly plug it up with a rubber plug (if you are fast) or use a plug like this http://www.poolweb.com/Home/Other-Produ ... 3-4-Washer

plug up the hole with that blow thru plug and then use a compressor until you see bubbles come out the main drain.

OR!

because I hate that style all together, swim down and plug off the main drain at the bottom of the pool and then suck out any water you can from the main drain hole in the skimmer and then fill the void with pool anti-freeze.

 

[rickmnj]

Kevin,

Thanks for the reply. Funny enough I used to dive down to cap off the main drain but I'm afraid those days are over. The water is pretty cold and for some reason the pool is deeper than most residential pools. Whenever I went through the effort to cap the main drain I always thought to myself, there's got to be a better way.

So, I think I'll go the blowout plug/compressor route.

Curious on another thing, could my main drain and spa drain be interconnected? There are three pipes going to my pump. I know one is for the skimmer we're talking about. I believe another is for the far skimmer and then there's one more pipe. I'm guessing this is for the main drain and(?) the spa....? Is this a common configuration?

Thanks again!

PS: I went to school many years ago with a young lady who had the same last name. I'm not thinking it's a common surname.

 

[X-PertPool]

Maybe take some pictures and post them. That might help try to figure out what goes where. Sometimes those older pools make me scratch my head with what they were thinking when they plumbed them.

 

[Melt In The Sun]

rick, as you said above your drain is plumbed through one of the skimmers. The third pipe is almost certainly the spa drain only.

 

[rickmnj]

OK, that makes sense. I will confirm this weekend. Thanks for connecting the dots.

However, I'm puzzled at how water is pulled from the main drain, into the skimmer, and then up to the filter. I'm thinking the way the main drain is connected to the bottom of the skimmer it would be quite "passive" with no real draw.

 

[CUTiger78]

However, I'm puzzled at how water is pulled from the main drain, into the skimmer, and then up to the filter. I'm thinking the way the main drain is connected to the bottom of the skimmer it would be quite "passive" with no real draw.

It's the magic of hydraulics! I don't how it works either, but mine works the same way and, I've got a real, good draw from the main drain. With the diverter in place in the skimmer, I've used the main drain to drop the water level 2+ feet below the skimmer.

You do have the diverter that facilitates this magic, don't you?

 

[rickmnj]

I just had the pool renovated and both skimmers replaced. I have to check to see if a diverter was left with the other misc materials. I'll venture a guess that it's a tube that connects the two "ports" together.

 

[mas985]

However, I'm puzzled at how water is pulled from the main drain, into the skimmer, and then up to the filter. I'm thinking the way the main drain is connected to the bottom of the skimmer it would be quite "passive" with no real draw.

Water cannot be pulled but is moved by being pushed from higher pressure to lower pressure. A pump works by removing water from the pump basket which in turn lowers the pressure in the pump basket. The higher pressure of the air pushing down on the pool surface then pushes water through both the main drain and skimmer. As water moves along the path from the pool to the pump it loses pressure until it reaches the pump basket which has the lowest pressure in the plumbing system. In the pump basket some pressure is also lost so at the port where the main drain is connected to the skimmer, that pressure is less than atmospheric so some water will still flow from the main drain to the skimmer basket. There are usually flow controls at the bottom of the skimmer as well as a float which helps to equalize the flow between the skimmer and main drain if desired.

On the return side of the pump, the pump creates higher pressure/head with flow rate which then forces water through the return plumbing back to the pool. So the lowest and highest pressures in a pool plumbing system are on either side of the pump impeller.

In reality, this is no different than sucking on a straw. Liquid is not being pulled up the straw but instead a partial vacuum is created in the mouth which then allows the liquid to be pushed up the straw by atmospheric pressure.

 

[rickmnj]

Wow, thanks Mark. I'm sure I'm not the only one who's learned something here today.

 

[CUTiger78]

I'll venture a guess that it's a tube that connects the two "ports" together.

Naw, it looks like this:

Never tried to load an image before, so if it didn't come through, go here:
http://www.yourpoolhq.com/catalog/produ ... mage/1249/

The first summer I had my current pool, I didn't figure this out for weeks.