Is the siphon standpipe opening sitting lower than the open channel standpipe opening (like this picture appears to be
http://www.beananimal.com/media/4070/standpipe-close.jpg) or are they sitting even (like this picture appears to be
http://www.beananimal.com/projects/silent-and-fail-safe-aquarium-overflow-system.aspx) ?
The bulkheads are all at the same level. Fairly recently, issues where reported that there was a starting issue, for
some systems, that did not fall into the "mold" or pattern of mistakes made in the implementation of the system.
This set pattern is: Pipe outlets more than 1" below the water level in the sump, (number 1,) the air vent line too low in the overflow (number 2,) air leaks in the main siphon (number 3,) and horizontal runs under tank (number 4.) If these four mistakes are avoided, there is no reason in the world for the system to not start as it should, showing up as an unusual delay in the main siphon kicking in (sudden drop in water level) or the main siphon not kicking in at all, and excessive flow through the open channel. It is perfectly normal for the system to take a minute or so to kick in fully, but much longer than that, there is a mistake in the individual implementation. There are no mystery casues for start up issues, and the system implemented as designed, does not have inherent issues either in normal operation, startup, or in one of the several failsafe modes. As a single solution to a very old problem, it does not get any better. Simply put, if you ignore opinions on the desgin, build the system as designed, you are not going to have problems with it, and there is certainly no reason to deviate from the design, by raising the open channel higher than the other two holes.
Back to the "mysterious" startup issue. Most systems that show this issue, along with having one or more of the big 4 going on, have 1.5" bulkheads, and are running rather low flow rates e.g. running way below 1200 - 1500gph, at around 200 gph perhaps up into 400gph, maybe even more. (Based on provided information on the system.) Statistically, there are very few systems that are actually flowing higher than 1000gph, and even fewer getting up into the 1500gph range.
A 1" bulkhead will allow, depending on pipe size, up to around 1500gph, with a normal head height of around 24" + with 36" upping the value quite a bit. Therefore, the use of 1.5" bulkheads should be reserved for systems that target above 1500gph, and perhaps even 2000gph.
As a possible fix, Bean suggested raising the open channel by a half an inch. The logic is too increase the head pressure on the siphon, making it easier for the siphon to purge the air. The fix does work, and with a system taking for instance 5 minutes to fully start, the start up time drops to ~ 1 minute, which is the normal startup time for the system (IME anyway.) I would suspect, that the lower the flow rate, (ignoring bulkhead size) the more advantage there would be to this modification, but I have not investegated the thought. This of course all assumes that there are no other implementation errors, though most often it is not just a single problem, rather multiple problems with the implementation.
That being said, if the system is built as designed, such modification is unnecessary, and just complicates the process of implementation, and adds another layer of confusion, to a system that should not be confusing, and is simple to implement...that is the whole point to the system, and the manner in which it was presented. Is the actual startup time all that critical? I don't think so. If it takes a minute, so what, if it takes 5 minutes, so what...so long as the system starts fully, and the fail safe systems operate properly, and when they should, the startup time is irrelevant. It is just a forum debate point, with little to gain...
