I would imagine a "herbie" overflow is refering to the act of using a partialy closed valve to create a siphon that is just slightly slower than the return pump, then using a second standpipe to draw off the remaining water. I am not sure how herbie gets credit for the concept... but I guess if you post it on RC before anybody else....
If you are doing this without a THIRD emergency drain, you will awake one day to find water on the floor.
You should never rely on a siphon without an emergency drain. So I am not sure what a "sorta" herbie overflow is. I just hope it is not a siphon
In any case the details of such an overflow are important: What follows is my standard post on a siphon assisted overflow. If you do this correctly it will be DEAD SILENT. You will not hear any water moving and will have absolutely NO AIR BUBBLES in the sump.
This type of overflow is PERFECT for a coast to coast type setup or any large external overflow box. IT WILL NOT WORK on a SPLIT overflow. The (2) main standpipe MUST be in the same overflow box. Read that again.... THEY MUST BE IN THE SAME OVERFLOW BOX. The third (emergency drain) standpipe can be anywhere.
2) of the overflows will have down turned elbows that are 1/2" or so off the bottom of the overflow box. The third one will have an upturned elbow with a pipe (if needed) and strainer on it. The idea is to set this just above the normal operating level of the overflow. All (3) will leave the box and connect to a TEE. The Tee will have a threaded cap adapted to the top (so it can be made air tight but removed). All three caps will be drilled and tapped to accept a john guest valve. All (3) tees will have ball valves right below them, then a Union fitting. The drainpipes will connect from the unions to the sump and be sumberged about an inch.
The ball valve on the first standpipe will be partially closed and the john guest valve fully closed. This will cause the standpipe to draw a full siphon.
The second standpipe valve will be all the way open and the john guest valve all the way open. The john guest valve will have a piece of airline attached to it. The airline will curl back over and be clamped inside the overlflow just below the rim of the tank.
The third standpipe valve will be all the way open and the john guest valve fully closed.
Here is how it works:
The first standpipe is adjusted so that it draws a full siphon but not quite enough to suck the overflow dry and gurgle. The ball valve on this standpipe is where you make water level adjustment for the overflow. There will be no air drawn into the standpipe and no bubbles in the sump
The second standpipe handles the little bit of flow that is left over. Becuase the valve is open, the standpipe will not be able to start a siphon. Becuase the flow in it is low, it will be silent and not carry any air to the sump.
The curled over airline is there just in case the water level in the overflow rises to "flood" level. If this happen the airline will go under water (in effect closing the john guest vavlve to air) and the overflow will then try to start a siphon. This will clear the overflow box and make a nasty flushing sound. This will cycle until you fix the blockage that almost caused the flood.
The thrid stand pipe is there just in case the other two can not handle the flow. For example, your lazy and don't take care of the algea. A huge mat breaks loose and sucks into the two active standpipes. The third will take over.
I hope that helps.
Bean
