Closing above ground pool: need to blow out main drain??

VTPooler

Member
Jul 30, 2020
9
Vermont
Hello all. Happy weekend!
I'm closing my pool for the season and have a few questions.

My usual closing plan is

Balance water/ Shock pool
drain the pool below the return line disconnect the filter/pump lines
put air pillows in place
cover the pool
bring the filter/pump inside

This year, I have a heat pump, so will disconnect that amd bring it inside as well.

I've never blown out the hose to the main drain. I read the pool school page on closing above ground pools and I didn't see any mention of blowing out lines, but have seen recommendations to do so elsewhere. It's never been a problem, but I'm wondering if I should start blowing out the that line. Thoughts?

Every year, I use 3 air pillows. Most years, Im lucky if one is still inflated by the time I open the pool. I'm planning on skipping the pillows this year. Should I maybe leave more water in the pool or have some other plan?

Thanks,
Mike
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
7,652
NY
I read the pool school page on closing above ground pools and I didn't see any mention of blowing out lines
Most above grounds have removable flex pipe that can be taken off, shook empty and stored.
I've never blown out the hose to the main drain.
It will not hurt to start now. It can only help.
I'm planning on skipping the pillows this year. Should I maybe leave more water in the pool or have some other plan?
Without pillows I would personally keep the water higher, but its no harm either way.
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
13,479
Houston, Texas
Whether or not you should drain the main drain depends on how deep the frost line is in your area. Its easy enough to plug a main drain in an AGP if the underground line breaks. If you get long, deep freezes where you spend days below 0 then blowing out the drain is good for peace of mind.

If you cover the pool you need to be sure not to anchor the cover to the skimmer box. If you use the type of cover with grommets and a cable and winch to tighten it up, leave the skimmer exposed and keep the cable above the skimmer. If you run the cable below the skimmer you run the risk of ice weighing down the cover and causing the pool wall to buckle. Personally once all the leaves are off the trees I would leave the pool uncovered. Fill the skimmer with chopped pool noodles so that any water that collects will compress the noodles and not crack the skimmer. My 2 cents on covering an AGP for winter!
 

VTPooler

Member
Jul 30, 2020
9
Vermont
What's all? Thanks for the feedback.
UPDATE:
I am going to use a pillow. Turns out I still have one left and read some stories about expanding ice busting some pools, so not going to risk that. Hopefully it lasts long enough to provide protection.

I am going to try to blow out the main drain line with my shop vac. Pool is 7200 gallons, 12x20 x 4 ft rectangle, so hopefully that works.

Can someone explain the physics of blowing out the lines to me? Having a hard time getting through my thick skull how the air pocket keeps the line free of water. How long before the water is out do I need to close the open end of the line before the air pocket is gone and water is back in the hose? Sorry for the dumb question!
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
7,652
NY
Can someone explain the physics of blowing out the lines to me? Having a hard time getting through my thick skull how the air pocket keeps the line free of water. How long before the water is out do I need to close the open end of the line before the air pocket is gone and water is back in the hose? Sorry for the dumb question!
So first things first the drain pipe needs a valve so you can seal it off while still applying air/pressure to the pipe. Without a valve, a bazillion pounds of water weight in the pool will force the newly empty main drain pipe full 100 times faster than you could ever take the blower/vac off and cap the pipe. So if you are applying constant air to hold back the water in the drain pipe and close that valve, said air is trapped in the drain pipe and the pool water can’t push past it. Your above ground pool has different physics to it because your main drains are just below ground level and mine are 8+ feet deep, But that’s the general basics.

The natural assumption is that high PSI would clear the lines but with a good length of pipe, you need a constant flow of air and as little as 5psi will do the trick if the air supply never stops. This is why the exhaust port of a shop vac works while a small/cheap compressor doesn’t. Compressors have to be relatively big or of great quality to maintain continuous CFM (CCFM).

If the water height is drained past the skimmers/returns then you only have to empty the pipes. With the main drains you are fighting all 7200 of your gallons trying to fill that pipe. which is why you need to trap the air inside.
 

VTPooler

Member
Jul 30, 2020
9
Vermont
Thanks Newdude. It's a flex hose and there is a shutoff valve on it. Attached is a picture of the skimmer with the main drain attached to it. The blue shutoff valve is on the main drain line. I plan to disconnect it from the skimmer, pop the shop vac on exhaust through there and close the valve when done and attatch it to the deck with a bungee. Think that will do the trick? I also bought some antifreeze, but not sure if it make sense to use in this scenario. Thoughts there? Should I put it in before attempting to blow out the line in case the blowout only partially works?
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
7,652
NY
I plan to disconnect it from the skimmer, pop the shop vac on exhaust through there and close the valve when done and attatch it to the deck with a bungee. Think that will do the trick
Without having a cyclone blower which is usually the only one that has the power to completely clear the main drain line, I think your plan is as good as you can get. Maybe because yours is at or near ground level the shop vac will have an easier time, ideally you would see bubbles coming out the drains, but that’s probably too much for the shop vac.
trick? I also bought some antifreeze, but not sure if it make sense to use in this scenario. Thoughts there?
Given months of sitting there it will find it’s way into the pool and be diluted beyond usefulness before it would freeze anyway. It works in the skimmer/return lines because they are usually isolated from the pool water at that point. Only the water left in the pipe can dilute it and at 4:1 Or 1:4 that’s still a good ratio of antifreeze. At the same time, dumping a gallon into the main drain pipe will not hurt either. So feel free to do it just on the rare chance it stays on the high end of the pipe. I do ‘just because’ things all the time and would not point a finger at you. Lol.
 

VTPooler

Member
Jul 30, 2020
9
Vermont
Hey New Dude. Thanks for your help on this. Wound up closing last week, although not sure it was the right move with unseasonably high temps near 80 this weekend here in VT! Maybe I hold out until Oct next year. I was spending about $10 / day keeping the heater on, which seemed wasteful, so decided to stop and close, but maybe next year I'll just leave it open with the heat off towards the end of the season and see what happens.

Either way, tried blowing out the main drain with the shop vac. No bubbles, but seemed like I was able to get some air in...however the valve didnt completely seal and it slowly leaked out. So instead I just went with what I usually do and what the pool store that installed recommended, to disconnect the main drain hose and anchor it to my deck above the pool water line. They also suggested dropping a small hose with what I believe is a cork in one end, to give expanding ice something to crack, if need be. They also mentioned that the main drain line is installed below the frost line. Seems a lot, as I think the frost line is about 10 feet here, but I guess its (hopefully) part of their installation process to get it below.

So the pool is closed, thanks for your help!
 
  • Like
Reactions: Newdude

Soximus

Active member
Sep 28, 2020
28
Connecticut
Pool Size
17656
Surface
Vinyl
Chlorine
Liquid Chlorine
Personally once all the leaves are off the trees I would leave the pool uncovered. Fill the skimmer with chopped pool noodles so that any water that collects will compress the noodles and not crack the skimmer. My 2 cents on covering an AGP for winter!

Don't cover the AGP! I love this idea. I'm a brand new pool owner-- I'm planning on starting a thread on how to best cover it (it has a deck around part of it that makes "typical" covering impossible), but... is not covering it at all really an option??
 

Enjoying this content?

Support TFP with a donation.

Give Support

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
13,479
Houston, Texas
All the cover does is reduce the amount of stuff that falls into the pool. Covering an above ground pool doesn't prevent it from freezing solid. and if it is covered improperly ice build up can damage the walls.
 

Soximus

Active member
Sep 28, 2020
28
Connecticut
Pool Size
17656
Surface
Vinyl
Chlorine
Liquid Chlorine
Interesting. Does the precipitation and ice build up over the course of the winter matter at all? Or does evaporation take care of things.
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
13,479
Houston, Texas
Interesting. Does the precipitation and ice build up over the course of the winter matter at all? Or does evaporation take care of things.
If you remove or seal the plumbing, drain below the level of the skimmer and return, and fill the skimmer with material like cut up pool noodles that will compress when ice forms, ice or precipitation build up in the pool shouldn't negatively impact the pool.
 
Thread Status
Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.