Blowing out bottom heater vents

[jt100]

Hi,
I have a 20000 gallon in ground vinyl pool with 2 bottom vents. One is in the bottom of the deep end and the other is on the slope just past the shallow end. When I blow these out, I get bubbles coming out of one (the vent with least resistance) and not the other. Since there is no way to seal that to blow out the other vent, will it be sufficient? I close the valve as I'm blowing the line to create an air lock. I assume most of the little water left will be well below the frost line? Any help would be appreciated.
John

 

[Catanzaro]

When I blow these out, I get bubbles coming out of one (the vent with least resistance) and not the other.

Can you please be a little more specific? You are blowing out air from where and which one is blowing out first and are you capping it? Is it a main drain? And are both these bottom vents returns or on the suction side? If you do not see bubbles coming out, you can not create an "air lock". And an "air lock's" water line should be below the frost line.

What type of vent do you have that you can not seal? Maybe a picture from the internet would help?

 

[jt100]

A little more detail. These are flat return vents on the floor of the pool (similar to photo below). When the heat pump comes on, the returns auto switch from the wall to the floor. the idea being that hot water mixes better and is coming from the bottom of the pool. At the pump there is a valve that can switch between the wall returns and the returns on the bottom. My normal process is to blow all the wall returns and cap them. I will then switch the valve to the bottom return vents to blow those. But since i cant cap them the air will only blow through the bottom return with the least resistance. (unless there is a way to cap them?) There is no bottom drain and 2 skimmers.
thanks again

 

[Catanzaro]

I will then switch the valve to the bottom return vents to blow those. But since I cant cap them the air will only blow through the bottom return with the least resistance. (unless there is a way to cap them?) There is no bottom drain and 2 skimmers. thanks again

Now, I understand. The least resistance is probably closest to the valve and equipment pad. What exactly are you using to blow air? Compressor or Shop Vac? You could try building pressure (if you are using a compressor) and then opening the valve up to see if the second floor return starts bubbling? If so , you can create another "air lock" on both floor drains. Is this your first year closing the pool, and if so, maybe you can find out who closed the pool before and what equipment they used? I do not believe floor drains would have caps (too hard to get down there).

It may be that your blower does not have enough volume to move to the second floor drain. This year, I turned on my blower and the first return started bubbling. Because I was explaining to my friend how I close my pool, second return started bubbling. By the time I walked over to the pool, the third return started bubbling. As I closed off each return, another started bubbling. I was moving quickly and had goggles on. Each return took about 30 seconds to cap off (at most). This tells me that if left long enough, the blower will move air along the next, of course starting first with the least resistance. I had all 8 returns open and they are quite long runs. I do not use a compressor or shop vac, but the Cyclone. Maybe, it is that you need more volume to get to the second floor drain.