Main Drain Air Leak?

stowner · Postby **stowner** » Wed 22 Apr, 2009 10:35

I have just opened my in-ground 5m x 11m pool for the season. If I open the inlet valve ahead of the pump for the two skimmers, with the main drain valve closed, I can prime the pump easily and the water flows exactly as it should and to the right pressure. So far so good.

If I open the inlet valve for the main drain with skimmer valve open, or open the main drain valve only, I get no water into the pump at all. I have only run the pump for no more than 2 minutes. It normally feeds through after about 40 seconds.

I have checked the strainer lid and re-greased the seal.

The pool is not leaking. The level has not dropped over the past three days.

I therefore conclude that either:

1. I have an air leak on the pool side of the drain pipe that is above ground (otherwise the pool water level would be dropping); or

2. It takes more power to draw water from the main drain, and the pump has lost some of its power. Although I discount this as unlikely as the water flows just great using the skimmers with the main drain valve switched off.

3. Or I have a blockage in the drain pipe. Not sure how this can be as it was working when I closed the pool and I close off any open pipes to prevent small animals from using them as winter burrows.

Am I right? Or is there something else I need to check before I get a pool company in to start digging up the pipe?

Postby **ChuckGeo** » Thu 23 Apr, 2009 06:52

It sounds like you may just have air in the line from the pool being winterized. You might want to try getting the pump primed on the skimmers, then open the main drain valve a little bit - perhaps 5%. Does air appear in the pump? If it does, and the pump continues to pump water, leave at this setting for 10 minutes to see if the pump eventually draws the air out of the main drain line and it starts operating normally - if it does, slowly open the main drain valve to pull out any remaining air until hopefully it runs normally, air free.
If you're unable to clear the air out of the line, and you confirm no air leaks on the main drain side above ground, you may have a leak in the main drain line. The only way to confirm this is through a pressure test of that line.
If the main drain cover is in place, the line is probably not clogged. If it is clogged, you should be able to run air free with the skimmer & main drain valves open, but the flow should stop immediately when the skimmer valve is closed and restart when the skimmer valve is re-opened

Good luck.

stowner · Postby **stowner** » Thu 23 Apr, 2009 16:05

Thanks Chuck. I found the problem - hair line crack in the main drain pipe that comes out of the ground before it then bends into the plant room. I found it by pouring what into the strainer and allowing the water to run back into the pool. Small droplets could be seen on the pipe. A quick patch using duct tape showed it was the cause as the water from the main drain flowed through nicely afterwards. So this weekend I will be replacing a small bit of pipe.

deepeanuts · Postby **deepeanuts** » Wed 17 Jun, 2009 23:10

Dear Chuck, we just re-plastered our pool and fill it with water (today) only to discover there is now a leak in the main drain. We tried the different methods mention above 5% - 20% etc. and assessed for air in the line. Is
it possible something got damage during the re-plastering? Also what would be reasonable charge to have someone pressure test the line? And would we have to drain the 26,000gal pool? thanks

Postby **ChuckGeo** » Thu 18 Jun, 2009 05:38

It's unlikely that the main drain line was damaged during a replaster, however it is possible to get the line clogged with plaster. A diver should inspect the main drain sump and make sure the line isn't clogged. If it's not clogged, the diver can plug the main drain line so it can be pressure tested. In my area the cost to put a diver in the pool and pressure test the main drain line would be $220. - $330..