location of main drain pipe

[PoolDoc]

It would make sense that builders would follow a consistent pattern in the way the locate pipes . . . but in my experience that's not true. I've seen pipes run just about every way they could have been.

About the only thing you can rule out, is any path that would have required the builder to cut through rock.

You *might* get some indication of how it runs, if you dig down and follow the line for 6 feet or so away from the equipment pad.

One caution: the MD pipe COULD run under the entire pool, to reach the drain. OR it could run around the walls (from either side) and then drop under the pool. For several reasons, there's a fair chance that the section under the walls is the location of the leak . . . and fixing a leak their is a major task. Usually, it's easier to run a new line.

One suggestion: verify that your pool's hydrostatic pressure relief fitting and valve ( IF it has one ) is not the source of the leak.

[sks24]

Thank you for your reply PoolDoc. I don't think I have any kind of pressure relief fitting. Here's my equipment pad, and here's the top of my sand filter. When I try to turn off the skimmer with the pump running, and open the valve so that water can come from the main drain, the pump loses its prime because it sucks in air, presumably from the hole that's in the MD pipe (which, again, must be at the same level as my returns less @ 4 inches). I can bring a little water in from the MD, but only if about 75% of the intake is from the skimmer.

My main drain intake at the bottom of the pool does run off to the east, which is the side of the pool that the equipment pad is on. Here's a pic of the east side of the pool.

What comes to mind is to start digging just south of those black chairs that you see (that's the east side of the pool (I'm looking from the north)). If I'm lucky, the pipe runs under the concrete deck where the deck is relatively narrow, and the leak would be easily and safely accessible and repairable.

Running a new MD line would involve digging under the pool all the way to the bottom drain hole underneath the pool, no? This would no doubt require a permit, and cost thousands? I've seen solutions which involve running a new liner inside the pipes. Are there companies which sell kits to do this, or is there a DIY pipe liner solution? I saw one company, but apparently they're out of business.

The soil around this pool is very sandy, and so the digging would be easy to do by hand.

Again, thanks for your help with this matter.

[PoolDoc]

The hydrostatic valve, if there is one, is in the bottom of your main drain:
http://www.a1poolparts.com/-strse-83...lve/Detail.bok

[sks24]

I think there may be one in the MD next to the intake. I think I recall seeing two elements: the drain intake, and something else, which could be the hydro valve. Tomorrow I will dive down there and take a look at it. I think that there could be an "O" ring failure such that it would allow water through until the water was shallow, after which there wouldn't be enough pressure to breach the O ring. So that could account for the very specific level to which the water descends. But the inability to draw water exclusively from the MD? It seems like that air would have to come from a hole in the MD pipe.

Thanks.

[PoolDoc]

When hydrostatic valves fail, often it's because they've opened, and allowed ground water to flow into the pool -- what they are supposed to do -- but also allowed a bit of grit or organic matter to enter, and wedge the valve open a bit.

[sks24]

I didn't look at that drain today to verify whether there's a hydrostatic valve there. But I'm pretty sure there is, not least because when I drained the pool completely last month water would seep back into the pool via the MD, and very quickly. The water table is quite high here. I did try to remove the MD grate when the pool was empty, but there was no obvious way to do so.

Bottom line at this point is that it appears that the first order of business is to control for this valve. Since I don't have scuba gear, it looks like I need to drain the pool again, remove the BD grate, and just go ahead and replace the valve using the valve tool they sell at that site you linked to above. I guess I'll buy a new grate, too, since I might have to destroy the one which is on there now to get it off.

But my inability to get the pump to keep its prime if I try to pull more than about 25% of the water from the bottom drain concerns me. It seems like the only circumstance which could account for this would be a hole in that MD pipe.

A somewhat related question. I noticed a new problem yesterday on my equipment pad. When I run the pump with the selector which is on top of the sand filter set to either "Filter" or "Recirculate" some water leaks out of my exhaust drain. It seems like the handle is pretty hard to turn on that selector. What might be causing this? This just started yesterday. Here's a pic of the flow with the selector set to "Filter" : https://drive.google.com/file/d/0B4q...it?usp=sharing

[PoolDoc]

Bottom line at this point is that it appears that the first order of business is to control for this valve. Since I don't have scuba gear, it looks like I need to drain the pool again, remove the BD grate, and just go ahead and replace the valve using the valve tool they sell at that site you linked to above.

Do NOT drain the pool when the water is high; even concrete pools WILL float out of the ground. If you must drain, you MUST lower the water level around the pool.