Okay,
couple of things that I can see quickly.....
Check valves.......these things have NUMEROUS reports of failing when you need em most. I wouldnt trust em, unless you mind the occassional flood or your house is made by rubbermaid.
Ways to prevent back siphon that dont involve check valves....
Drill small (1/16 or so) holes in your return lines, (where they are in the tank), so that air gets sucked in and breaks siphon if you have a power loss. Things to remember/keep in mind.....I would go w/ at leasat 2 holes and clean them RELIGIOUSLY....like once a week. If something clogs the joles, its like they didnt exist at all. Snails can be in the wrong place at the wrong time, so I would plan for multiple holes.
You can also raise the height of your return so that it cant suck down that much water in the event of a power loss. Ensure that your sump can handle the back siphon volume. If you're going w/ a closed loop any way, this makes a little more sense to me, since the closed loop can handle the water movement inside the tank and now your return's only job is to...well return water to the tank from the sump.
Closed loop........some people love SCWDS......I've heard several instances where they have become jammed internally w/ debris etc when used on Closed loops, since there is no filter media to catch the crap before it gets in the plastic gear teeth of the SCWD. I personally havent used one, so I cant speak from experiance, but I am not taking the chance. I'm going w/ one of
these. I'm using the 4 way Heavy Duty Oceans Motions unit....ALOT more expensive than a SCWD, but a lot more reliable too......also a lot cheaper than a motorized ball valve.
One last thing...why two closed loop pumps? I believe it would use less power to run one big pump than two little ones....
HTH,
Nick
