<a href=showthread.php?s=&postid=11657564#post11657564 target=_blank>Originally posted</a> by bromion
With that setup, you should use check valves.
You can avoid using them if your return bulkheads are high in the tank. In that case, when the water level drops, the reverse flow ceases. In this case, it will continue to drain until the water level drops below one of the return nozzles (assuming they are on the same plumbing). Even worse, loc-line is not always water tight. Over time, some algae or something may pry open a seam in the loc-line well below the nozzle, meaning water would continue to drain from that point.
To make cleaning the check valves easier, you can use unions on either side, or buy check valves with integrated unions.
Exactly.
Thanks for the pics i2go. That helps a lot in the attempt to offer constructive advice.
As I suspected, the return bulkheads are on the bottom of the tank.
I too would be uncomfortable relying solely on a check valve to stop your tank from emptying on the floor in the event of power outage or return pump failure.
Two options, if you are inclined to avoid the need to use check valves, which I certainly agree is IDEAL, are:
1. You could hard plumb pvc to those bulkheads to near the waterline and then run nozzles keeping them close to, or within an inch or two, of the water line. If done proficiently, that would eliminate any risk of a leak beneath the lowest return nozzle.
Bromion is correct, loc-line in not necessarily water-tight. Any leak in the return plumbing inside the tank, regardless of how small, beneath the lowest return nozzle will eventually drain the display tank, to that point, in the event of a prolonged power outage.
This would mitigate the possibility of the tank draining below the level of the return nozzle (unless of course, you experience some type of very unlikey catastrophic bulkhead failure on those bulkheads at the bottom, in which case the entire tank would spill on your floor) and you should verify that your sump capacity can handle whatever amount drains/siphons back to your sump if/when you loose power. Yes, drilling a small hole in the loc line just below the waterline will break siphon. Simple to test really, just get your tank set up and running and cut all power to your tank and note how high your waterline goes up in your sump. Then mark your maximum fill line appropriately.
Or,
2. you could cap off those return bulkheads on the bottom and either drill your back pane at the upper corners for return bulkheads or run your returns over the top. Ideally, you'd drill your hole for the return bulkhead(s) in the bottom of inside your overflow, but I doubt you'll have room in there. Your tank is acrylic, so it would be extremely easy to drill.
HTH
Yes, those TOTM's are something to aspire to and take away ideas from, but those tanks are usually VERY well-thought out ahead of time and properly drilled/plumbed to avoid the neccesity for check valves. I guess every scenario/set up is a bit different and needs to understood fully when making suggestions.
