Frozen water: Rubber Expansion Plugs vs. Threaded Plugs

MostlyCanuck

Bronze Supporter
Mar 19, 2021
122
Toronto, Ontario, Canada
Pool Size
15000
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Vinyl
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Hi all

By now I think I've established that the rubber expandable plugs are by far the most common / industry standard for winterizing lines.

However, I recently watched a video from a guy in the industry who made a good point, conceptually. He contends that threaded plugs are safer because when the water level is lowered to approx return level, when the water freezes it can grab the wing nut of the rubber plugs, ripping the plugs out and hence opening the line.

Can't find the video any longer, but he also explains it here: Things You Need To Close A Pool

Has anyone ever experienced this at all? If there's some truth to this, a threaded plug would sound like a safer bet, wouldn't it?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,117
Northern NJ
Pool Size
35000
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Plaster
Chlorine
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Pentair Intellichlor IC-60
when the water freezes it can grab the wing nut of the rubber plugs, ripping the plugs out and hence opening the line.

I think that is an OWT.

Ice expands over water by 10%. It hardly has enough force to "rip a plug out". If a plug fell out then it was not securely put in place to begin with. Good excuse for a pool guy to use when he messes up.
 

Bperry

Gold Supporter
Aug 20, 2020
1,012
Knoxville, TN
Pool Size
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Plaster
Chlorine
Salt Water Generator
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CircuPool RJ-60
Hi all

By now I think I've established that the rubber expandable plugs are by far the most common / industry standard for winterizing lines.

However, I recently watched a video from a guy in the industry who made a good point, conceptually. He contends that threaded plugs are safer because when the water level is lowered to approx return level, when the water freezes it can grab the wing nut of the rubber plugs, ripping the plugs out and hence opening the line.

Can't find the video any longer, but he also explains it here: Things You Need To Close A Pool

Has anyone ever experienced this at all? If there's some truth to this, a threaded plug would sound like a safer bet, wouldn't it?
I like the threaded plugs cause they are way cheaper and don’t leak or have rubber that wears out and leaks.
 

MostlyCanuck

Bronze Supporter
Mar 19, 2021
122
Toronto, Ontario, Canada
Pool Size
15000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
I think that is an OWT.

Ice expands over water by 10%. It hardly has enough force to "rip a plug out". If a plug fell out then it was not securely put in place to begin with. Good excuse for a pool guy to use when he messes up.
lol yeah maybe it is nonsense. wonder how many ppl here ever found their returns unplugged by moving ice and the rubber plugs at the bottom of the pool... and maybe if they did the plugs weren't installed all that well as you say..

anything wrong with threaded ones though? I mean, if there is a chance that the rubber ones fall off (whether due to ice or human error), aren't the threaded ones a safer bet as long as the o-ring is intact and lubed for a good fit? I had posted my question as I was struggling to understand why the rubber expandable ones have become the most common / tool of choice...
 

1Sammy

In The Industry
Jul 20, 2017
438
Windsor, Ontario. Canada
A LOT of buts ifs and ANDs to answer that. If you are for some reason draining below the returns taped threaded plugs can be used. Trying to use them without lowering the water the air will tear off the tape before you can get the plug in. Especially on the last one. So for underwater plugging the rubber plugs are much easier to use as no tape needed. Frozen water aka ice, lol, around either can for sure cause issues IF it wanted to. The ice would either have to Lift or Drop. IF that happens it could shear either one of them off. Ice / frost can lift a brick 2 story house causing doors and windows to jam so those little plug won't stand a chance IF, that's IF, the ice moves. Although not good for a liner pool i "think" this is why some people drain Below the plugs and keep the water below all winter as other then that there is no need to drain off all that water just to install plugs. Keeping the water level high, as i do fyi, and well above the returns there is no control as to how deep the freeze will be.
 

VTpc

In The Industry
Jan 1, 2021
5
Vermont
I think it depends on where you are, I only use threaded plugs with plumbers tape unless there's a gunite fitting or an equalizer below the skimmer. I'd rather replace an o ring than have to use a new test plug each time, but both get the job done they just have their quirks. I also do use the underwater, you just have to keep a finger on the tape and be quick about getting it threaded in so that the tape doesn't come off. I have found test plugs (expandable rubber plugs) on the bottom of a pool during a few different pool openings, but I think it's more likely that the safety cover got caught on it and popped it out while the cover was getting pulled than ice pulling the plug out.
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
11,229
NY
Threaded plugs or blow through duck plugs (also threaded) are best underwater. They might be more expensive but $7 (?) for many years is negligible. Anywhere above the waterline (including where the waterline might become with off season rain if applicable) can use rubber plugs. Like the equipment pad for example if you have any open pipes. Those pipes won’t be threaded and rubber plugs are your only option.
 
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