I hear ya, however I too find some misinformation with your post.
First, This system is neither, it is 'The Todd'.
Please point out the "mis-information" in my post...
In the BA, you have a full siphon, and the secondary takes up some of the extra to keep the primary running on siphon without sucking the overflow dry and sucking air- right?
Wrong. The open channel (what you call "the secondary") is a buffer. It provides a "self adjustment" feature to the system. Because it is operating in open channel mode (not restricted, not siphon) the flow rate can rise and fall with changing flow rates in the system overall. Such changes can be due to several conditions including variations in the return pumps output, or simply a change in barometric pressure. The siphon line cannot handle an increase in flow rate, because it is restricted by a valve, therefore it does not dynamically adjust. The two pipe system, and the Herbie modification suffer from this problem and require periodic adjustment to compensate because these two systems are not self adjusting.
If flow through the system decreases, flow will decrease in the open channel; if the flow rate decreases sufficiently, water will stop flowing in the open channel, and further reduction would result in a lower water level in the overflow, and the siphon may suck air. The open channel cannot prevent this, and in your modification, the open channel will not prevent that either.
If I"m not mistaken- this secondary in fact has a airline the is used as mine is (that's where I got the idea), and turns the secondary into an unobstucted (no gat vavle) flow to the sump under siphon when the air tube end also gets underwater.
It does have an air line that trips the open channel to siphon mode, under certain circumstances.
This is 'The Todd' system.
The BA foes further-usually using smaller diameter drains so that the 3rd line COULD be used- when H*LL freezes over.
It is actually quite the opposite. The BA does not go further, it is the standard, "The Todd" stops short of incorporating one of the important safety features of the drain system. This safety feature is actually, the main safety backup for the system: the dry emergency; the "open channel" tripping, is the last line of defense failsafe. The failsafe (the air vent line) has only one failure mode: plugging up, which results in making the system safer, rather than creating a flood. The definition of a failsafe.
On 'The Todd'- It uses large diameter lines, and when you completely shut down the primary- the secondary takes all the flow. And IF the overflow rises while air is being displaced in the downtruned elbows (to keep it silent)- the overflow rises and the end of the airline goes underwater it quickly turn it into a full 1.5" unobstructed (no gate valve) drain and at a 9.5' drop, that probably flow close to 2000/hr +.
I've shut the primary many times/tests- the secondary works as stated and quickly drains the overflow.
A 1.5" bulkhead with a 9.5' drop will have the capability of flowing ~ 8000gph, not accounting for friction losses. This flow will exceed the resonable limits for a gravity drain, 1.5" pipe size (18f/s.) The friction losses would be extreme, the pressure losses would be extreme, and it would most likely water hammer, creating a great deal of noise and possible plumbing damage. 3" pipe would be a reasonable pipe size for this sort of flow... 8400 gph limit @ 6f/s.
A 1" bulkhead with a 9.5' drop, has a flow capacity of around 3600gph, but again, this exceeds the reasonable limits for 1" pipe of 960 gph. (6f/s) However, with 1.5" pipe, this reasonable limit goes up to 2100gph. (6f/s) This system could be pushed into the 3000gph range, with minimal pressure losses, and minimal noise.
As designed, Bean's system uses 1" bulkheads, and 1.5" pipe. This makes for a very wide bandwidth (depending on the length of the drop) from a few hundred gph up to ~2000gph (assuming a normal drop of 24 - 36",) which is more than adequate to accomodate 90% of ALL hobby systems, including your 9.5' drop and 2000gph (if you actually have that flowing up to the tank.) What other significance you are placing on the bulkhead/pipe size, is unclear...
Nothing wrong with a 3rd 'redundant' emergency drain however.
If itever sees water- it's because the secondary eith the air tube isn't adequate enough for the given flow.
* When I posted about my new tank and needing to drill a third hole, a few people quickly PM'd me about only using the 2 large diameter holes I already had- and glad I did it this way too.
Folks are afraid of drilling additonal holes, or simply do not wish to make the effort, not that there is anything advantageous to using two holes rather than three. It is done via pm, because posting in open forum will draw comments involving safety concerns. It is called bad information/mis-informaton/ based on a misunderstanding of how the BA system works, or merely personal opinion.
*If the Herbie uses a siphon and a 'dry' secondary- how would one keep from sucking air in the primary? Surely the secondary takes some water to keep the primary running on siphon. Otherwise you'd be readjusting your gate vallve all the time, and it would be a PITA.
If it uses the siphon and dry emergency backup, it is implemented the right way. Everything else is improper implementation. The fluctuations are not quite that frequent, unless the pump is showing early signs of failure, or the barometric pressure changes every 5 minutes... and if they are, some other implementation error was made. Generally, unless pump failure is involved, the fluctuations are not large enough in magnitude to cause the siphon to suck air. Nonetheless, the Herbie modification , or two pipe system, is not 100% stable, and needs periodic adjustment. This is what gave rise to Bean's system, however, in the "update" the backup and failsafe features were maintained and improved. The admonishment: All three pipes must be used, is clear, to the point: black and white—no gray area.
And I understand this thread is all about the BA, 3 drain system.
I learned a lot form this, and will return your receivers back to their normal broadcasting, and I'll start my own thread on the forum perhaps on it.
Unfortunately, there was a failure to understand the basic operation of the BA system.
I was merely showing my alternative- 'The Todd' overfow.
Everyone, that posts in favor of the so called 'modified BA', or self adjusting Herbie, and variations of the same such as "The Todd," that include a trickle of flow through the DRY emergency, share the same basic misunderstanding of how the BA system actually works, and why it is designed as it is. They all assume the DRY emergency is a "redundant" back up. This shows that the information is all coming from the same source, the author of which does not understand how the BA system works, and like most, probably never read the first page of this thread or Bean's article on his website, that explicitly explains how this system works. Nor have they read the part of Herbie's thread that states that a DRY emergency is an essential part of a safe siphon drain system.
To wit: In Bean's system, the DRY emergency is the MAIN emergency backup subsystem. A pipe with water flow (irregardless of how much) is a plug risk; a DRY pipe is not a plug risk. When the main siphon plugs, and during startup, the DRY emergency will take the flow. This happens because the open channel cannot trip to siphon due to the placement of the air vent line (higher than the inlet to the dry emergency.) If this vent line is placed lower than the inlet to the DRY emergency, the system will not operate properly: the main siphon will not fully start (can't purge the air) as the open channel takes most of the flow. If both the siphon, and DRY emergency become occluded, the water level rises to cover the air vent inlet, and the open channel trips to siphon mode. The open channel is every bit as much of a plug risk as the main siphon, which is why the DRY emergency is the main emergency backup.
The Todd: This system has no emergency
backup. If both the siphon and open channel plug, the water goes all over the floor. The Todd (or any variation thereof) is not exempt from the plug risk involved with water flow in pipes. An added air vent line will not mitigate that risk. As I said before, we can argue the statistical probability of failure all day long, but that is irrelevant. The fact is two pipes can plug, at the same time. It can happen, and it has happened. Otherwise none of us, that do know how these systems work, would have a concern over it.
The Todd: This system could also present the "air vent line too low" startup issue just the same as the BA system. Since there is no DRY emergency to mitigate the water level, the air vent line inlet can be submerged easily as startup, tripping the open channel to siphon, before the main siphon purges air. This will cause the main siphon to not fully start. This is a very common complaint throughout this thread, with systems that have not been implemented properly.
The Todd: Because it has no DRY emergency, both pipes have water in them, the system has no
failsafe, redundant or otherwise.
There are many, many ways to implement a drain system. Probably as many as there are hobbyists to implement them. To date, only a few can be considered safe in terms of the long standing guideline: "Never run a siphon without a dry emergency backup." Many folks choose to ignore that guidline, and it is a personal choice. Many encourage others to ignore that guideline as well, to dimiss the risks involved—that should be considered bad advice. It is some else's system; some one else has to bear the cost of a flood. It is irresponsible. In the end, it only creates confusion within a topic that is complex to begin with. Evidenced by the number of folks that don't understand how these systems work.
Eventually, someone will come up with a better mousetrap than the BA, albeit they will have to get up pretty early in the morning to get a headstart.
However, for such a system to gain anything over the BA or Herbie's corner overflow modification of a two pipe system, it will have to incorporate the same level (if not more) of backup and failsafe features. Such a system does not yet exist.
