Herbie Overflow Fail

[Seth81]

So I have been testing my setup for my new 190 Gallon bow front tall deep tank, and I just realized that I made a really bone head mistake in my Herbie style overflow. I wanted to post this so that others do not make the same mistake that I did.

Here is my current over flow setup ( I don't show it but the sump is in the basement):



Two 1.5" standpipes one has a gate valve to control flow and is meant as the primary and the second as the emergency flow just incase the primary gets plugged. The basic theory is that the water line will be somewhere between the two pipes and the primary will be fully submerged and in full siphon but the second will not be submerged at all. In theory this setup should be completely silent because no air gets sucked in.

The big mistake I made was combining the two drain lines after the gate valve. The reason why this is a mistake is because due to the Venturi effect the flow of water down stream of the valve will create a vacuum on the backup stand pipe and will suck in air along with the water from the primary, which then breaks the full siphon causing the water to flow less quickly. Eventually the water level in the overflow will raise to the emergency level and water will then flow with air down the emergency line causing a horrible sucking and gargling sound.

The only reason I combined the lines in the first place is because my sump is in the basement and I wanted to limit the holes I made in the wall. I am now considering making another whole and making the emergency a completely separate line. Does anyone have other suggestions?