[untamed]

Originally Posted by mark

Just a couple of additional thoughts regarding this diagram...

1) The primary drain line (the one with the ball/gate valve) is shown in this diagram to have a tall standpipe up inside the overflow box. That pipe isn't necessary. In fact, I don't think it is a good idea. Optimally, the water level in the overflow box operates at some point which is ABOVE the primary drain, yet BELOW the emergency drain. In this diagram these two drains are very close in height, providing little room to operate.

Further, if there isn't enough water depth directly above the primary drain, then it tends to form a vortex and suck air down...which defeats the entire purpose of the design.

2) As I just mentioned, the diagram shows the water level at the level of the emergency overflow. That's OK, but the system works more quietly at a water level slightly below that.

If you ever want to come by and look at a variety of Herbie overflows in operation, just let me know. In my refugium, I have a standpipe on the primary overflow. It is there for a very specific reason which I can demonstrate to you.