Blowing out main drain? Friendly debate

[weird_tolkienish_f]

I have seen advice on the main drain, how to blow it out. When I first bought this house, I found as other's have that I could not get the drain to bubble no matter what. I talked to the previous owner and he has said he just sealed up the main drain. This I did not want to do. I have also discovered that pouring a gallon or so of the RV antifreeze seems to be heavier than water (maybe on purpose), and it actually seems to evacuate your skimmer of water too. I poured some antifreeze into the skimmer (which had water in it and the skimmer to filter line was plugged) and the antifreeze actually went down the main drain line and even emptied the skimmer of water. I could also see some blue antifreeze come out of the bottom where the MD line was.

I do not believe that the MD has a leak in it, because I have found that I can run my pump entirely with a diverter valve, with the waterline of the pool actually below the skimmer, and the pump does not "lose prime".

I read stories here about people applying 20-30 lbs of pressure on the MD line trying to blow it out and it seems to me that they may actually be doing more harm than good. Are the lines designed to take that much pressure? (Not a rhetorical question, I have no idea).

My current regimen is to pour a gallon of RV antifreeze down the MD line and seal it up for the winter (in addition to normal blowing out of lines).

 

[samt]

Yea it funny all the different methods people use. I think a lot of people are just learning and trying different things until they find something that works for them instead of going out and dropping $300 on a pool blower.

As far as the 20and 30lb to blow the MD. I agree, not me, I really don't do anything other than hook up my pancake compressor and turn it on. Its only .8 hp and it pushes air through the line fine. 7 ft deep end, 60 ft of pipe.

Does it get all the water out like a cyclone blower? No, there's still some water in the pipe, but it's below frost line.

I think some people just have a undersized compressor or shop vac and no matter what they do , it just isn't enough.

But they tend to figure it out and it's just the learning curve that there going through now.

 

[Catanzaro]

Did you close your own pool, or have a professional (that is what they call themselves) do it? I also have read that schedule 40 PVC piping can handle at least 90 lbs. of pressure. Although, I would not take any chance of having something fall apart and cost a lot of $$ to fix. Low pressure and high volume is the answer to blowing air through the lines.

 

[mas985]

I also have read that schedule 40 PVC piping can handle up to 90 lbs. of pressure.

Where did you read that? Schedule 40 PVC can handle quite a bit of pressure but it does depend on size:

PVC Pipes - Pressure Ratings

 

[Catanzaro]

I only mentioned 90 psi as a number, it was not anything specific. I just recall that PVC can handle quite a bit. Should have not quoted an exact figure. Based on you pressure ratings, it appears that even 1" piping can absorb a lot more, unless I am not understanding the chart. How does the primer and glue affect the pressure?

 

[mas985]

Typical 2" plumbing has a bursting pressure of 890 psi. So not really an issue for air pressure.

Glue joints, if done properly should be just as strong if not stronger than the pipe itself because of the double thickness of the pipe wall at the joint.

But all this is a bit moot because you only need 3.5 psi to clear a pipe 8 ft below water level. Bursting due to air pressure is a non-issue.

 

[MarianParoo]

Can one of you guys comment on the "blue" anti-freeze? I thought RV was pink only.

 

[Catanzaro]

Typical 2" plumbing has a bursting pressure of 890 psi. So not really an issue.Glue joints, if done properly should be just as strong if not stronger than the pipe itself because of the double thickness of the pipe wall at the joint.But all this is a bit moot because you only need 20 psi to clear a pipe 8 ft below water level. Bursting is a non-issue.

Mas:

Thank you for your quick response. Has there ever been any studies done showing how much force ice expansion creates before pipes burst? I know there is information on residential piping through homes, but never have I found anything directly related to swimming pools. In theory, can piping that is encased in concrete with water still in it freeze and cause the piping to burst, especially if 3' down. Most piping in residential swimming pools is enclosed in concrete (called the collar). Thanks!

Can one of you guys comment on the "blue" anti-freeze? I thought RV was pink only.

This one I do not know. I do not use the Anti-Freeze when I close my pool. This was the first year that I actually closed it. Last year, the PB did it for $288 dollars. (ouch). That was the cost of the chemicals for the whole 4 months (TFP Method)

 

[mas985]

Has there ever been any studies done showing how much force ice expansion creates before pipes burst?

First off, the bursting comment I made was about using air to blow out the lines and not about water freezing in the pipes. But for freezing, it is all about pressure too. When water expands during the freezing process, it can cause very high pressures and burst the pipe. However, the water needs to be contained and have nowhere to expand. In pipe, water will freeze from the outside in towards the center of the pipe and in most cases, there is a path for the pressure to escape. If both ends of a pipe are closed off with a valve or solid ice, then this pressure can build and burst the pipe. Also, there only needs to be a little over 10% air volume in the pipe to prevent bursting.

In theory, can piping that is encased in concrete with water still in it freeze and cause the piping to burst, especially if 3' down. Most piping in residential swimming pools is enclosed in concrete (called the collar).

Freezing water can crack concrete but the conditions need to be right. As I mentioned before, there needs to be blockage in the pipe before the pressure can build and burst the pipes as well as the concrete. Also, the frost line needs to be deep enough long enough to allow for the pipes to freeze. In your area, most frost depth maps do indicate a remote possibility of freezing temps at that depth. But if the pipe is encased in gunite, then the gunite has to get down to freezing temps too and usually water will not even start to freeze unless temps are well below freezing for fairly long time. There is a lot of latent heat in the ground, gunite and water which have to be removed before anything even starts to freeze below ground.

Extreme Frost Depth (m):

 

[Husky25]

Can one of you guys comment on the "blue" anti-freeze? I thought RV was pink only.

Some pool anti-freeze is blue. I've picked it up from time to time. Your liner maybe blue, but water is clear and there is enough contrast to make a distinction in color when you're adding it. Especially if you've already blown out the lines.

 

[Catanzaro]

Mas985:

Thank you for your quick response. I am aware that the pressure was not related to the freezing of pipes and this is why I asked the question. I have always understood that water expands 9%, so your 10% statement makes a lot of sense. So if a pipe is 3' in the ground, half full of water, parallel to the ground, and the water freezes from the outside in towards the center, will the ice then expand upwards, and not out? If this is the case, then even if water does freeze in underground pool plumbing, one should not have any issue with bursting of pipes.

 

[mas985]

So if a pipe is 3' in the ground, half full of water, parallel to the ground, and the water freezes from the outside in towards the center, will the ice then expand upwards, and not out?

Yes. In this case, the water would probably freeze at the bottom of the pipe first pushing up the water as it goes.

But also, in general, the water will expand wherever it has space to move into and it will move formed ice as long as the ice does not reach a physical barrier. PVC pipes are very smooth and the PVC ice boundary is not very strong so even if ice forms, it can move along the pipe fairly easily as long as there is an air gap to move into. So even with a vertical pipe and the bottom of the pipe sealed off and with ice forming on the water air boundary at the top of the pipe would expand upwards as water continues to freeze below the ice cap.

 

[Catanzaro]

Mark:

Thank you. Enjoy the remainder of the week.