uncle - thanks for all the feedback.
DSB & Caulerpa:
Interesting that you mention Caulerpa since that's what I was thinking of planting. My most succesful sump evolved into a canopy of Caulerpa that was overflowing with cocepods that kept my fish and corals well fed. So, the plan is to achieve shadow and avoid digging roots with a suspended eggrate canopy. This also helps with the trimming of the overgrowth. The idea is to put the refugium on an off-cycle lighting as well. I also agree with the idea of keeping it clear of any other animals that can feed on the bed (love Ron Shimek’s article).
Good luck with that, hope it works out for you. The number 1 reason for DSB's going bad is improper setup and improper management.
Durso v. BeanAnimal
I've looked at both and I'm not sure I see the vast difference in the physical implementation.
The appearance of the two systems is similar, however the operational characteristics are very different.
Both consist of three overflows, two of which are bent down and the third is an emergency that points upwards.
For clarity, there is only ONE overflow; either in or coming out of that single overflow there are three standpipes/drains.
In the BA version, all three have water valves.
Only one valve is required--in the siphon drain line. The other two were a convenience, that Bean felt would be advantageous in terms of maintenance. The only valve used, is the valve on the siphon.
In my version of Durso, the emergency is intentionally open.
Durso, is the name given to a particular design of standpipe, invented by Richard Durso. The standard capped tee, with a down turned elbow, and air hole to allow air to enter the standpipe. This design solved a particular problem for him, however, he did not understand or know anything that governs the operation of air assisted drains (of any style, Stockman, Glass-Hole style, what have you,) by his own admission.
The two bent down overflows in both designs have caps. Durso has air valves at the top of both and BA has an air valve on only one. Having both an air valve and water valve on both siphons allows for individual tuning of air and water flow.
Again, the valve in the open channel, is not used--it is left open. A partially closed valve in an air assisted drain line, creates turbulence (air and water mixing) that causes the noise, bubbles and instability associated with ALL air/water standpipe drain systems. Water flow tuning is accomplished with a valve on the pump output, not by restricting a drain line. It presents a plug risk, which is why BA's system uses a fail safe and a redundant fail safe, that each individually--have a higher flow capacity than the main siphon.
The BA approach essentially provides an optimized solution where one air valve (middle) is completely closed and the other air valve is completely open.
No, it is an implementation of a siphon system, using two redundant fail safe's, that self adjusts. It is not an optimized "durso" setup.
Then the middle water valve is used to ensure a full siphon through that drain.
No, the valve on the siphon line is used to raise the water level in the overflow, after the siphon has started, so a portion of the flow leaving the tank, flows through the open channel (durso, air/water mix, whatever you wish to call it.)
The drain with the open air valve is intended to carry very little water flow to avoid gurgling and bubbles.
Yes it is indeed intended to carry a small portion of the total flow. It is low, because if the pipe is more than 1/4 full of water, it will start making noise, bubbles, etc. The stand pipe is vented to prevent it from becoming a siphon, and is used as a "buffer" to allow the system to handle variations in flow rate--without the need to make adjustments to the flow to keep the siphon from breaking, or keep the tank from overflowing--or in this case, keep the dry emergency dry, unless there is a plug in the siphon line, or other such emergency. The tubing from the open channel is a trigger, that when submerged, causes the open channel to become a siphon--the second fail safe.
Essentially, the physical implementation is the same. BA is a special case of the Durso with a proposed optimal state. I do like it and it makes good sense.
They may appear the same, however the implementation is different, the operating conditions are different and the capacity is way higher than a air assisted drain system. In the case of a 1" durso, the problem free flow rate is around 50 gph, (and such are not recommended for practical use) for 1.5" pipe it is around 350 gph. I can't say what it may be for a 2" "durso," I have never run a 2" durso, I converted exclusively (no small task for 100 systems) to siphon systems a long time ago--however once the pipe is over 1/4 full you will have problems with it. A 1" siphon will handle ~2000 gph with a 36" drop, and a 1.5" siphon will handle ~4500 gph with a 36" drop, 2" ~ 8000 gph. This is idealized to a point, and assumes no restrictions in the line. (smaller bulkheads, valves etc.
I think you need to study the BeanAnimal system further, and understand the physics that govern the operation of siphons and durso's. The difference between the BA system and a dual durso system is as the difference between night and day...
No offense, but it seems a bit silly to me to use an inferior drain system, when you are planning the setup to accommodate three drain lines, and the only modifications needed to your plans are eliminating 1 air vent, and two valves. The headaches you will save yourself: priceless.
Overflow sizing
I have three 2” drains. One of them is an emergency which should not be activated unless something goes wrong. I’m not sure I understand this statement “a single 2" emergency backup will not be much of a backup.”… how large does an emergency drain need to be? 2” should be able to handle a very high flow of water. I don’t know the limitation of a 2” pipe and would appreciate any external reference to it (couldn’t find one myself).
I am looking at this strictly in terms of capacity of the drains--2 - 2" drains vs a single 2" emergency.... indeed with the system you are planning, you will not be able to flow enough water through it without problems, to overpower the 2" emergency.
Horizontal drain
This is a legitimate concern and my plan is to keep it very short. The total drain drop will be about 3ft (water in overflow to water in sump). The through wall distance is about 1ft. I don’t like this ratio, but it’s unavoidable. I plan on using a 45degree connection under the tank and another at the sump to avoid going really horizontal… 1ft drop down + 1ft down and across + 1ft down. This will force the hole in the wall to be larger… I don’t see an easy fix for this.
I pretty much guarantee the horizontal portion will cause you problems, especially with air assisted drains. With a siphon system it may or may not cause a problem. It is a known issue with both styles of drain systems.
Sump to Sump imbalance
This is a very good point and is actually intentional. The connecting pipe is a 2” diameter pipe and the travel is about 2ft. I want to keep the sand bed sump always submerged. To do this, the connection there is well above the sand bed ensuring that it can never siphon back lower than the top of the pipe. The first sump is really for holding a large volume of water. It allows me to perform water changes of varying sizes without impacting the living system. I can close the skimmer inlet and the valve between the sumps and then open the main drain valve. This would evacuate the first sump without changing the sand bed sump or the main tank (return pumps off, of course). I can then open the valve to the water change tank and refill the first sump. Open the valves, turn on the pumps and I’m back in business in a few minutes.
Good luck with this also. That balance pipe is not going to handle the flow rate through this system--unless it is rather low. The flow rates I mentioned above, do not apply to your 2" balance pipe, nor the drain out of your second sump--you are going to have to have it sucking in air in order to get the surface water out--gas exchange issue. Systems like this seldom work as planned--there are far more reliable ways to move water from one area to another--which is why sumps use baffles rather than pipe.
You really should do some more planning and come up with a solution for water changes on the fly.
Your surge system is not going to supply adequate flow, to shut the system down--which brings up the question of a black out.......but both are another 2 page topic..........
Thanks for all the ideas and feedback. I really appreciate it.
I just realized I don’t have one way valves on the main returns! Easily fixed on paper (LOL).
Check valves can, do and will fail. It is a 100% probability--and you won't be around to stop the flood. Sound system design demands that the need for such devices is eliminated. A passive fail safe is required: sufficient empty volume in the sump to contain all pump off drain down. If it cannot, redesign it. Good system design 101.