Herbie overflow?

[sleepydoc]

If you have two holes of identical size, ... then essentially your emergency is "larger" than the siphon, since it doesn't have a partially closed gate valve on it - even though the bulkheads are the same size. As long as that emergency drain can operate under siphon without sucking air, you've got excess capacity in your emergency compared to the primary siphon...

The good news with all of this is that it's really easy to learn in a hands-on manner. IMHO, the biggest mistake you can make is to take a formulaic approach and build something you don't understand. There are LOTS of ways to run a reef tank, drain plumbing included. Building something you don't understand is risky. Instead, I think it's better to get your hands wet (literally). If you're trying to build something that can handle an emergency, simulate an emergency and see what happens. Block off your siphon with a rag and see what happens. Unplug the pump, then plug it back in 10 seconds later before the tank has drained down. Then do it again, but let the tank drain down fully this time. Then unplug the pump and plug it back in with the rag blocking the siphon, and see if the emergency can pull a full siphon from scratch. Think up any possible scenario, then test it, and adjust if you feel you don't like the result.

The restriction at the bulkhead can cause issues - one problem I had was with snails crawling down the emergency and getting stuck at the stricture. (They never seem to be able to figure out how to turn around and crawl back up!:hmm5 At that point, you're dangerously close to a complete obstruction and a flood.

Another thing to consider is that people frequently have the emergency drain close to the top of the tank. If it's within an inch or two of the top of the tank, it will entrain air and the maximum flow will be reduced.

I completely agree that being blindly following a formula is not ideal. Nothing beats actual experience. The variability in thanks and setups means rote formulas will likely never work for everyone. Unfortunately, a lot of people don't totally understand the physics of how the systems work, especially when they are first starting out. A formula at least gives them a place from which to start and learn the operation. Playing around and making your setup fail is also an excellent idea. Not only will it test the setup, but it will help you learn how it works.

 

[ca1ore]

Well circumstances vary of course. Not all siphons are materially constricted by the gate valve, and not all emergencies are dropped far enough down from the weir to develop
enough flow. Sage advice is to test your design to make sure it works as you expect it to.

 

[SFish]

Need to catch up and read your posts but what I plan is the two boxes connected by a 1 1/2" bulkhead. For the main drain I am going to go with a 1" pipe and for the emergency I am going with a 1 1/4" pipe and bulkhead. For my return flow i'm go for around 500gph.

 

[SFish]

I was planning on having the bottom of the weir on the inside box to be at about the height of the bottom of the outside trim with a wet emergency drain about 1" below that. As far as animals getting in the overflow box I was going to make a lid and have weir on that as well. I also wanted to make the boxes all black.

 

[SFish]

Does this seem ok to everyone?