[quote author=sfsuphysics link=topic=3677.msg51529#msg51529 date=1218220870]
The fact you have two drains it's not too much of an issue, but all you need is a little something clogging one drain (or worse both) then your "correct amount" becomes too small, and depending upon your setup that could cause an overflow. I've seen it many MANY times with people restricting drains because it was too loud, rather than doing a proper standpipe.
Why does the main drain have any restriction at all though? I can understand a fuge having a restriction because you don't want as much water going through, but the mian sump drain shouldn't be restricted. If there's too much water going into the tank from the return, tee off your return and put a valve on the tee to restrict how much water goes into the tank, but not your returns. As I said unsure what you mean by "correct amount" but if you're trying to match your drains to your pump you're in for a major headache down the road.
Two philosophies of mine involving drains. 1) Over side for the job, don't match to your pump, be able to handle 2 or 3 of those pumps worth of water (usually that involves 1.5" piping). 2) Have a backup that's not used at all, if it's not used it can't get clogged, you simply have it a tad higher than your main drain pipe so if that does get clogged the backup can kick in as the water level rises.
Again not trying to give you crap here Roc, just since Mark is hooking his up a little advice to throw his way (unfortunately via you
). What I would have done with your setup, obviously larger drain pipe, unless of course your return pump is tiny, is to tee off that return, one to the sump one to the refugium, with a ball on the refuge side only.
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Having one drain restricted is the whole point of the flooded drain design. The idea is that the drain which is restricted runs at full siphon, taking the vast majority of the flow. Because its lower in the overflow box and running at full siphon, it draws no air so it's completely quiet. It needs the valve in order to prevent it draining too quickly and sucking in air.
The second drain, which Roc has running to the fuge, should always be wide open. It's capable of taking the full flow if there's clog in the first drain, but normally there's very little flow in it so it's also very quiet.
A standpipe reduces the flow of a drain as well, and it too can clog. I would question the inclusion of the second valve (on the higher up drain which runs at low flow) but as long as it's kept wide open when the pump is on, it seems fine.