Overflow Flow Rate Problems

[BeanAnimal]

Rich

Thanks for your input into this matter. I think before herbert and I get into a fight next time... we should both be talking about the same thing, instead of different things by the same name.

I would argue that most dursos are not built that way (bulkhead the smallest point) even if they should be. This also brings to attention the fact that an "external durso" can not be a "durso" unless the external down pipe is further restricted compared the the bulkead where it leaves the tank.

Now lets get back to that "head" question. If the elbow is only to silence the durso, then the hole in the cap can never be to big, it can only be to small (forming a partial siphon). If this is the case, then there should never be any air introduced into the sump from the durso (even without a cap). Otherwise, we are not dealing with static head pushing water through the pipe, we are dealing with the free fall of water, or a turbulant flow of some sort. If air is being sucked or pulled down, then it is either due to turbulance at the surface and high enough velocity to pull the air down (decreasing flow) or from a partial siphon or vortex.

I would also agree (and have stated several times) that using a siphon to get extra capacity out of a system is asking for trouble. The drain system should be able to handle the full return pump flow without the aid of a siphon.

My reading has also lead me to believe that head in a standpipe is somewhat self correcting in the fact that increased flow will raise the head, but also increase the drainage rate. I would imagine this relationship is non linear and very dependant on many factors. If you are depending on the bulkhead to provide restriction, then there is no extra capacity in the system except for relying on a siphon.

So it would follow that some "durso" work very well if all oif the vairables fall into place, the rest of them are either oversized or undersized for a given flow (if your postulate about their operation is true). The durso site (and Richard) goes to great lengths to explain how to tune the air in a durso... but as stated above and following your explanation (and herberts theory) THERE SHOULD BE NO ADJUSTMENT. ( Again, this is likely where the real crux of the arguement started)

All in all, I think there is a lot more to a silenced standpipe than meets the eye and a "durso" is only a "durso" in some of the cases according to your explanation or theory of operation.

Thus the answer is still not there

Bean

 

[BeanAnimal]

Redfish... thanks for your post. It is nice to read a well authored reply (as compared to some of the crap myself and herbert write).

 

[Redfish]

It wasn't crap. It was a very passionate discussion where you both knew you were correct based on experience and knowledge. You guys were beating up on each other over way different principles and trying to mix about three different ideas into one argument.

Those last few posts including Bean's and Herbert's I think were both right on the money. Particularly your attempt at describing the Durso charachteristics. And when I say attempt, It doesn't mean wrong, because you are as right as anyone can be. The dynamics of trying to introduce exact amount of air into the freefalling water versus flow and piping size in order to eliminate the vacuum are impossible to accurately sum up. It is all a big guess. The purpose of the hole is to provide an input for air so that the gulping partial siphon doesn't form. If you make the hole to small, you cannot relieve the vacuum fast enough. If you make it too big there is not enough vacuum created and the water cascades (noisily) at high velocity in a turbulent manner down the pipe. Pipe size and flow rate are very important in calculating hole size. The guys that market these things have spent a lot of time narrowing the variables down. They can tell you what range of holes works for certain pipe sizes and flow rates.

My own personal opinion is that it is much easier to over size the initial bulkhead size (to eliminate sucking at this location) and rely entirely on a valve at the bottom of the disharge to create a pressurised column all the way up close to the bulkhead. You are basically removing Bean's turbulent water in the downpipe by limiting free fall availability. This is the only way I have ever been able to achieve long term near silence. It is cheap and requires little or no maintenance.

Of course I think people run way too much water through their sumps in most cases. If your skimmer pump will only pump 200 gallons of water into or through the skimmer, there is no reason to put more flow than that through your sump. If your using that return pump for circulation, you are just spraying that nice pollutant rich water you collected off the surface back into the water column with little or no treatment. I guarantee you will improve treatment efficiency by reducing flow to close to the skimmer capacity or less.

 

[Herbert T. Kornfeld]

"My own personal opinion is that it is much easier to over size the initial bulkhead size (to eliminate sucking at this location) and rely entirely on a valve at the bottom of the disharge to create a pressurised column all the way up close to the bulkhead. You are basically removing Bean's turbulent water in the downpipe by limiting free fall availability. This is the only way I have ever been able to achieve long term near silence. It is cheap and requires little or no maintenance."

-Redfish

I agree with you so much on that one you cant even imagine. If only I could put 3" bulkheads on every tank, or only run 100gph through a 1" standpipe then the whole world would be a better place. My whole attraction "low flow sumps" was pretty much started because of the near impossibility to quiet an overflow once the water velocity and water volume going down the pipe are high enough to start sucking in water. The taller an overflow, the faster water falls...so no amount of muzzling or capping will stop this, and as long as it happens, you will either have bubbles gurgling down below or a toilet bowl up above...one or the other. I prefer nothing more than trickling water down the sides of oversized pipes...but that doesnt seem to be the trend these days...at least not in the states.

The link below goes into more detail about our findings. Yes, low flow overflows are better for skimmers...it allows the skimmer to target the place where proteins build up as they oxidize...the surface...and lets nature work for you rather than an oversized skimmer.

http://reefcentral.com/forums/showthread.php?s=&postid=5416731#post5416731

As for you Bean...I await to see a pic of your setup...you got my attention with the whole 'oversized piping' once the bulkhead passes the bulkhead. Its a good way to 'cheat' the siphon effect, because with pipes that big (and 3 of them?) the siphon can stay in effect most of the time, but the few times it does purge, you prolly never even notice because it only has a few inches to form in and once it reaches the larger pipes it stops... Just a theory...gotta see a pic.

 

[BeanAnimal]

Hebert: I will post a few pics after I get some work done today. I

A bit more information on my setup:

(3) overflow standpipes

1" bulkheads with internal 1" street ells pointed down on 2 of the standpipes. (used to use strainers, but re-fiited the elboes so snails could not get under). The 3rd standpipe is fitted with an upturned elbow and strainer. It does not flow water normally.

The bulkheads are attached to 1.5 DWV sanitery tees and thinwall 1.5 PVC (likely shedule 40 or 80 would be a bit quieter simply due to thickness). Each downpipe has a valve below the Tee and then a union. From there spa-flex takes it into the sump. The outlets are submerged about 1/2" in the sump.

The 3rd overflow is for emergency or to handle a large wave device. As stated earlier, the air intakes for the caps are plumbed with JG valves and intake their air just below the tanks max fill level. This creates a redundant emergency flow system by causing a full siphon if the air intakes become blocked with water.

As you can tell from my description, this setup was designed to totally avoid a flood in the event that a pipe becomes obstructed. I had a flood due to RO/DI ASOV problems (before I built in redundancy to that system) and am not willing to go through a second one. My sump is also designed with 20 or so gallons of buffer space in case the fuge or other attached device becomes blocked or drains unexpectadly.

Bean

 

[dedfish]

The bulkhead is not always the smallest part. If your bulkhead is through the back wall instead of the bottom of the tank then you need to reduce the plumbing size some where about 12"-18" below the bulkhead. I have 2 1 inch external durso's that do not reduce the plumbing and I can't get them to handle ~700gph.

 

[Cuby2k]

Good discussion and enlightening. I am glad to see the different perspectives.

As far as engineers messing up projects Redfish, engineering is simply the education to know how far to over-engineer and to be able to do it faster than the other guy. Misunderstanding concepts is really the root of disagreement. Nicely presented, thanks for your input.

I have to laugh at tha_reids comment regarding the complexities of such small eco systems (or something like that). I really think that is why many of us are involved in this hobby, I know it is why I am. If it were simple it would not be as fun.

Our passions reflect our personalities and the diverse perspectives make it fun. Thanks to all.

Truth is you are all wrong.

 

[ninjafish]

Because there are a lot of new reefers that come across this thread - any discussion on standpipes and drains should include the Herbie method as well. It is vastly superior to any durso or stockman design - it will be quieter, safer, and easier to set up. The only downside is it requires two bulkheads.

http://reefcentral.com/forums/showthread.php?s=&threadid=344892

Not enough people are passing this info along...

- Chad