Lots Of Air Bubbles From Skimmer, None From Main Drain

[etbrown4]

We have a 30,000 gal in ground pool with a 1 hp hayward super pump and a sand filter.

Drawing only from the 2 skimmers we get no air visible in the pump housing during operation, but when we open the main drain inlet to the pump with the skimmers open too, we get a flood of air bubbles - really a torrent.

1. I know it seems obvious that there may be a break or a crack in the main drain line between the bottom of the pool and that diverter valve just before the pump intake, but is there any other possible explanation? There are no known water leaks or unexplained water loss. With no water loss wouldn't that suggest that the main drain line is intact - at least up to the pool top water level?

2. If you can keep the pool clean just drawing from the skimmer baskets, do you really need to open the main drain during normal operation?

Thanks for any expert tips!

[Pool Clown]

A blockage in the m/d line could give you these symptoms too.

[brettnolan]

Not sure where you are located, but if you have just recently opened your pool and there was water in it (however much you left in it over the winter) it's not likely you have a leak in the underground plumbing (that's generally not terribly likely anyway). You could have a blockage as Pool Clown suggested, or you could have a BAD air leak near the equipment pad on the line to the MD.

One quick way to check is to open the valve, turn on a water hose and run water over all the fitting on the MD line. If the bubbles go away, you know your problem is there. Can be quick-fixed with silicone, but a better fix would be to re-plumb that line to the air leak.

And yes, you can run the pool without the MD. Due to the new VGB rules, we are starting to build pools without MD's.