The tank doesn't have corner overflows. It's a center overflow, with the 3 bulkheads in it. I know a coast to coast is ideal for a BA system, but I didn't know if it was a requirement. I have looked at the herbie before, just thought the added emergency drain of the ba was worthwhile. That being said, if a herbie will fit in my overflow box, there's no reason I can't extend one of the 3/4 pipes just above the water line, correct? Isn't that the only real difference between the 2?
No, it isn't. Since you are not getting the correct information:
You have to be careful with common information available concerning the Herbie modified drain system, and how it compares to a BA. Even after all these years, too many folks get it completely wrong.
Both systems incorporate a DRY emergency backup drain. No flow is put through this drain, in normal operation. Otherwise it is a plug risk, and not an emergency backup. The Herbie is not stable, and the water level in the overflow will fluctuate, with changing ambient conditions, etc.
Bean noted the instability in the Herbie modification, and took steps to mitigate the instability. He incorporated what has come to be known as an "open channel" into the system to provide a self-adjustment feature. The open channel is a Durso standpipe, (with air hole.) He also used some tubing from the hole to act as a trigger to "trip" the open channel to siphon mode (no air in the line,) in case the both the siphon and DRY emergency failed. Both of these modifications, as well as making the system rock stable, added an additional layer of fail safety, making it the safest drain system in use today.
Siphon drain systems have been around a very long time. They predate both the Bean, and the Herbie, as well as the Durso. Richard Durso, invented the Durso, to both mitigate the water fall into the overflow (why siphon standpipes were being used) but also to mitigate the flood risk involved with siphon standpipes. He did not understand the physics of his design, and the rest, as they say, is history. The rule for running a siphon standpipe was/is never run a siphon without a DRY emergency backup. There is no ambiguity in that rule: DRY is DRY, a "wet pipe," regardless of the amount of "wet," is not DRY, and therefore cannot be considered safe.
Herbie knew the rule. His design incorporated the obligatory DRY emergency standpipe. Bean knew the rule, and even though he added an open channel (durso) to the setup, he still included the obligatory DRY emergency, and in no uncertain terms stated that all three standpipes must be used. Why? Because a drain with water in it is a plug risk. There is no ambiguity in that, and the statistical probabilities are irrelevant. A system is either safe, or it is not safe. A lot of folks are very put off by the lack of ambiguity, believing for some reason that a confusing blend of 100 different ways to to do something is less complicated, than a subject being simply black and white.
Sometime after Bean published his design, suddenly the Herbie was being improperly implemented by allowing a "trickle" of flow through the DRY emergency. An attempt to incorporate the self adjustment feature of the BA, without incorporating either of the safety features. Ignoring the basic safety rule, chancing the odds, however one wishes to look at it. they ignore the fact that if the "trickle of flow" pipe occludes the system is going to flood, and there is nothing to prevent it.
Some of late have tried to mitigate that risk by using the air vent line trigger for the "trickle of flow pipe" or open channel, Durso. However, this is not very well thought out, and although a "step" in the right direction, if the open channel, "trickle of flow" pipe, Durso occludes, the system is going to flood and the trigger is not going to make any difference.
I know Bean has had the open channel fail, not sure if he has had both fail, but I have. If it can happen with us, it can happen with anyone, at any time. It only takes once, and by then, if you have "played the odds" it is too late, and it can be very expensive.
The difference between the Herbie and the BA is the open channel, not the DRY emergency. If you run the open channel, or "wet pipe" on a "Herbie" it is no longer a Herbie, and it is not a BA. It is something else. Folks do it, they claim there are no issues with it. That does not mean it is safe, nor does make it safe. I simply means some folks do it.
Beyond the open channel, the function of both systems is the same, based on size of the opening, pressure head, and friction loss. Some try to make more of a difference out of it, but it is a mis-application of the physics, and misses a few rather important points.
You don't have to read very much to implement either of these systems. In fact, reading too much is part of the problem. The information needed to implement either or both of these systems is on the first page of both original threads, and Bean's is also posted on his website. Bean's thread is very large and cumbersome to go through, reading (and understanding) the first couple of pages is all you need. The rest, fortunately or unfortunately is just rehashing, repeating, redundant questions over and over again. In between the redundancy is some very valuable information however, and skimming the thread is a very good idea.
