I'm replacing my liner for the first time ever, and have a bunch of water I need to get out of the pool. My aboveground has a main drain (as well as a dished bottom, so there is a lot of water). I should be able to get the pump running and backwash out the water using the main drain only, right?
I have the skimmer valve shut, the main drain open, the pool return closed, the sand filter set to backwash. The pump turns on, the sand filter seems full of water. The pressure valve on the pump is registering quite high, but I don't necessarily trust it. I should perhaps go get a new pressure indicator to see if the condition is real. When I add water to the pump skimmer basket to bring it up to the level of the pump intake, the level lowers and doesn't prime the pump. I can only get the water up to that level by closing the main drain valve to get started, then opening quickly. I did briefly see pressure on the backwash end at that time, so I don't think the filter and backwash plumbing is the problem. Also the pool is 10 years old and it has worked so far so there's no reason for the plumbing to be "wrong" now.
The water is silty but I have fished out any actual debris. I don't think there is a clog. I haven't seen any air bubbles coming up into the pool to prove it, though. The water is going Somewhere, and the pool is about the only place, unless there is a broken pipe under the pool, which seems unlikely.
Any secrets I should know about? Suggestions?
Eagerly awaiting your expert knowledge of fluid dynamics!