Oh, yeah, point taken. I can't think of a case where the second ball valve would be useful... even when the pump is shut off. Roc? Are there any times when you use it?
[/quote][quote author=pixelpixi link=topic=3677.msg51538#msg51538 date=1218225201]
[quote author=sfsuphysics link=topic=3677.msg51534#msg51534 date=1218224819]
No I dig the whole restricting one drain, but having two ball valves, that seems like it can restrict more than a single drain, even if it is 95% open.
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Oh, yeah, point taken. I can't think of a case where the second ball valve would be useful... even when the pump is shut off. Roc? Are there any times when you use it?
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Well this weekend when I did a water change. Since my rock work is fairly high in the tank and the top pieces have coral mounted on them, I will drain down a ways, but I shut off all flow from the tank, which includes the return, then I take the remaining water for the WC from the sump. When I start to put water back I put enough so it will drain back into the overflow then I open the drains back up and turn on the return pump, bingo everything starts working perfectly again.