I agree with Doug on everything except the hieght of the airline. It is best to have the end of the airline just above the emergency, not below it. So the open channel making a syphon is really supposed to be the last line of defense, Incase both the syphon & emergency get clogged. On some setups it doesn’t really matter, especially with exterior boxes because of the height differences between the standpipes. On other setups it can cause issues on startup. What can happen is the airline gets covered & empties the overflow box before there is enough pressure to purge the air from the syphon. It is better if the emergency takes a little water on startup because it won’t empty the overflow box & gives the syphon a chance to purge its air. Like I said, it isn’t a issue on all setups but it can be on others.
I think we tend to overthink things at times. Like Doug mentioned, the valve on the syphon is what sets the water level inside of the box but it is actually the open channel that determines the water level. On ghost type overflows with the pass thru holes & exterior box u usually want the water level 1/4 to halfway on the pass thru holes. There isn’t a point in being any higher & if u get it lower then the pass thru holes the waterfall entering the box makes noise. So set the open channel 1/4 to halfway up on the pass thru holes & set the emergency 1” to 1.5” above that as long as it is still 1” to 1.5” below the top of the box. It’s really pretty simple
I think we tend to overthink things at times. Like Doug mentioned, the valve on the syphon is what sets the water level inside of the box but it is actually the open channel that determines the water level. On ghost type overflows with the pass thru holes & exterior box u usually want the water level 1/4 to halfway on the pass thru holes. There isn’t a point in being any higher & if u get it lower then the pass thru holes the waterfall entering the box makes noise. So set the open channel 1/4 to halfway up on the pass thru holes & set the emergency 1” to 1.5” above that as long as it is still 1” to 1.5” below the top of the box. It’s really pretty simple
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