How do main drains work?

[cleancloths]

There could be another reason for the observation that the main drain is not doing anything. It could be a function of friction losses in the piping. If there are two skimmers in addition to the main drain the pump is going to pull from the point of least resistance, so all the water may be coming from the skimmers. If you partially close the valves between the skimmers and the pump it will force the pump to draw more water from the main drain. As a test you might want to close off the skimmers totally, when you do that the pump should pull exclusively from the main drain.

[abessellieu]

Whoa, you people are great. I do have two valves, I just didn't know what I was looking at. When my plumber connected up our new Hayward Super Pump yesterday he replaced most of the piping and put in two new red handled ball valves. They are in line with the pipes which means that they are both open. How do I tell which is which (skimmer vs main drain)? Or doesn't it matter? I'm thinking I can just shut one off and go and look at the skimmers - if they are still pulling water - I'll know I've turned off the valve to the main drain and vice versa. I guess my concern is if I guess right and turn off the skimmers first and the pump is only pulling from the main drains and the drains are clogged or collapsed, that I will be putting great strain on the pump, or somehow make things worse.

If it makes any difference to the answer, I'll tell you a little bit about the pool. We 'inherited' it with our house, and it was in poor shape. When we closed it up last year we knew that the coping was loose, the tiles were falling off and the skimmers were leaking badly. But as far as we could tell, the only leaking we had was at the skimmers. We would fill the pool halfway up the skimmer throat and the water level (rather quickly, like in a day or two) would drop to the bottom of the skimmers and stop. It didn't drop any further even if we left it for several days. So we felt it was worth renovating the pool since we were guessing that we had no major structural cracks or leaks around the drains at the bottom. We have since had it restored and had 35,000 gal of water trucked in two days ago. I have been watching the water level and there is minimal change (less than 1/4") and since it has been sunny and hot I am guessing that is due to evaporation.

So I don't think there are any leaks down there, but if it is clogged and I put all the pressure from the pump on them, what will happen? Or am I just being a worry wort (entirely possible)?

[cleancloths]

Just close the valve about half-way and see what happens. Then slowly close it more until you can determine which is which.

[abessellieu]

Yup - that did it! I now know which is which. It probably seems silly, but I was afraid to touch anything. Thanks so much. Now on to posting my chemical questions....