Overflow Flow Rate Problems

they are both the same. But you 'cheat' because you are showing them both reducing to 1" from 1.5"...with a 1" bulkhead and a 1.5: bulkhead. Lets say that both use 1" bulkheads, and then all 1.5" piping...then the taller internal overflow box would outperform the shallow one. That is the core of my argument with Bean. Of course, if both overflows are dialed in to try to maintain a syphon, their flows would be identical.
 
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kgross, and to add, the 2" standpipe/durso pipe makes the most restrictive point the bulkhead at its bottom at the bulkhead...the 1" pipe raises the restrictive point to the top. Im just thinking in terms of flow restriction as water goes down the pipe...

Also, keep in mind...I think Bean's standpoint is based on the idea that he might be using his drain system as more of a vacuum system than a head-pressure system...in which case what he says is 100% correct. I just dont understand why he would opt to do it that way...it defeats the whole purpose.
 
Actually THA REIDS, the flow will not be exactly the same depending on what piping you use,I could not tell you which one will flow more. The only reason being is that the 1 inch bulkhead creates a lot more friction loss than the 1.25 inch bulkhead, while the 1 inch pipe is 1.25 inch pipe and 1 inch pipe will create the same friction loss. But since the 1.25 inch bulkhead is close to the top of the water it will not get as much head pressure against it...... I think the first one will flow more water, but that is only a guess without pluging in lots of numbers to calculate the frictional loses in all of the fitings. The biggest problem with the first one, is that the way you show it you will not be able to create much for head pressure above the bulkhead. If you moved the bulkhead down even an inch or 2, it would flow more than the second one, unless your transition over to the one inch pipe was a very ruff tranistion. If you use a bushing that was tapered on the inside rather than square cut with the lower bulkhead you would get more flow than the second setup without any doubt. since for one reason you would have less tranistions in the flow while it has the higher velocity in the 1 inch pipe, each tranistion creates extra frictional losses.

Kim
 
Did you try to address one point or are you writing a book?


Pipe diameter does have something to do with head pressure. ...if the standpipe is too restrictive, the head pressure never has a chance to build up because the standpipe drains faster as the water falls further.

You are 100% wrong. If the pipe diameter is smaller then it stays full. A full pipe has head pressure. This is so basic, that it can not be overflooked. If you introduce air, then the head pressure disapears.


A good example, however unlikely, would be a 3/4" standpipe on a 1" bulkhead...no head pressure exists because the water never even builds up enough to gain depth pressure, right?

WRONG!!!! The system will be at full siphon. UNLESS you introduce air. Once the air is introduced, you are no longer working with head, you are working with free fall. AND YES A LARGER PIPE AND BULKHEAD WILL OBVIOUSLY FLOW MORE. Once again this is not a "depth" issue.


But with a 2" pipe on a 1" bulkhead, this is not the case. In this case the water can drain faster in the 2" part than the 1" part...so head pressure builds up (granted, if the flow is more than the 1" bulkhead could easily pass w/o buildup).


You have just shown that a 2"by1" system will flow more than a 1"by3/" system. Isnt this a givin. Again it has nothing to do with the depth.


So a good rule would be that if the standpipe is equal to or less than the bulkhead diameter, there is no head pressure
You are again 100% wrong. This is WHERE THERE IS HEAD PRESSURE.

....but if the standpipe diameter (or durso, whatever) is greater than the bulkhead, then head pressure builds up.

There is no difference between the 2 examples above (other than slight friction loss). The one with a larger diamter pipe may be quieter. They are capable of roughly the same flow becuse the bulkhead is th limiting factor. The smaller pipe may lose a TINY bit due to friction.

To restate what you said above...Head can depend on volume...not enough volume, no head at all. And since it is a ratio with pipe diameter...pipe diameter also has a role in head pressure...too much pipe diameter, no buildup, no pressure...nothing but FREE FALL there it is, LOL!

In that hard to follow statement, you made MY point. A durso is a free fall system so we are not dealing with head. It's that simple. Yes, you could adjust the durso to move water via HEAD, but that is a siphon. Something we don't want.

The rest is not worth commenting on, as it is based on incorrect assumption on your part.


I think the reason why you do things like this is something I see you often mentioning...using your durso as a siphon.

My durso IS NOT a siphon so your whole question.comment is moot. My system does not purge or flush. It runs at a constant level and runs very smooth. My donwpipes are larger than the bulkhead so the water free falls down to the sump. Air is adjusted by a john guest valve on each standpipe. The overflow is 3" deep and has 3 bulkheads in it. My return pump is a T4 (lets say 1000gpm to be easy). And I can easily shut down 1 bulkhead and restrict the second. Instead I have all 3 open so there is never a chance of a flood. My air intakes are setup so that if the overflow level rises to high, the intakes become submerged and a full siphon forms. This is a self adjusting flood preventer.

You have to adjust the air in a "durso" to tune it. To much air and you overflow, to little and you siphon. You will see people that have tuning trouble. I can explain why, but that is for a different post.

It should be as if we removed the durso part all together and just left a standpipe (and noise)...thats how a durso should flow...not with a siphon.

That is opposite of what a durso is. You are correct this is where we are having an issue. You don't see why the "durso" works like it does. The air is what what tunes a durso.

Bean
 
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Bean you are almost correct here, the only problem is that we are not dealing with static head pressure we are dealing with dynamic, ie with the water in motion.

Agreed Kim. However the largest force is the static head. A dynamic or energy head

IF the water is not moving at all so there are no frictional head losses you are correct, but since the water is moving there is friction involved. if you have a 1 inch pipe tyring to run full flow though a 1 inch bulkhead you will get a lot less flow than a 2 inch pipe trying to run full flow though the exact same bulkhead.

I fully agree, but this loss is minimal as long as the pipe is at least a large as the bulkhead. We are also only talking about a few inches of pipe here, so the effects are even further negated.

Regarding the water buildup against a bulkhead and the pipe diamter vs change in static or dynamic head. Not counting the mininal friction loss.... this all then depends on the amount of air being drawn into the system. If no air is drawn in, we are at full siphon and the bulkhead is the real limitation.

I think we all need to be talking about the same "standpipe" for any of this to make sense. It seems as if each of us is basing our explanations off of a slightkl different setup or parameters.
 
Herbert T. Kornfeld said:
they are both the same. But you 'cheat' because you are showing them both reducing to 1" from 1.5"...with a 1" bulkhead and a 1.5: bulkhead. Lets say that both use 1" bulkheads, and then all 1.5" piping...then the taller internal overflow box would outperform the shallow one. That is the core of my argument with Bean. Of course, if both overflows are dialed in to try to maintain a syphon, their flows would be identical.
Click to expand...

IF they both use 1.5 piping with a 1" bulkhead then yes, the right hand system would flow more under siphon. The left hand picture would be at free fall once the water travels past the bulkhead. This right hand picture would be at full siphon (head pressure). THIS AGAIN IS IF THE PIPE ON BOTH SYSTEMS IS LARGER THAN THE BULKHEAD AND NO AIR IS DRAWN IN!!!!


Once you start to draw air in at the top, both system will perform the same... .this is the point I have been trying to make ALL ALONG.

Bean
 
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I plan on using an exterior "Durso" style pipe like shown on the left. My reasoning behind this is not to give up valuable real estate inside my tank. Not to cheat but to try and reproduce a pipe that if cut in half would resemble Durso's design with 1.25" upper diameter and reducing to 1". Inside diameters should be equal for the most part (give or take 1/16). I realize that threaded fitting can cause a more drastic change in inside diameter causing friction and turbulence but I feel it will be a small dent in overall flow.I'm also running 2 of them with a 475gph return for safety reasons. I also debated on beveling the inside edges of fittings but I'm not trying to make this overly difficult. You guys will have me going for a full "port and polish" next :) If I were out for unreal flow rates I would just ditch the small pipe and step up to 2". I think the issue with the origanal posters setup is that he starts his "Durso" restricted (1" bulkhead).
 
My money is on bean, but who the hell am I to say. It appears though that although Herbert knows what he's talking about, he doesn't understand how a durso functions and thus his analysis, although correct, is ultimately wrong in this context.
 
Ok, ok, so how does a durso function then everyone? What about my knowlege about a durso is wrong? I thought it was to simply turn the water intake downward to get rid of the noise. If it wasnt for this noise, the durso would function exactly the same as a standpipe with the top removed. And then, to prevent a siphon from forming, an air inlet is introduced to the top. It seems that some of you are using this air inlet and downward facing inlet to create a partial siphon and boost the throughput of the overflow. Why would you do that? It defeats the purpose of a durso which is to eliminate noise. Sure, if a durso is used to speed up flow, then Bean is correct...but its not meant to...its not a reliable method, and there are better ways of doing this then since you are obviously voiding the noise cancellation.
 
The Durso is intended to reduce noise. However, since the flow from the return pump is constant, a properly tuned Durso should not affect the flow. If it did then either the water level in the tank would continue to rise lowering the sump level or the level in the sump would rise.

jm.02
 
"Pipe diameter does have something to do with head pressure. ...if the standpipe is too restrictive, the head pressure never has a chance to build up because the standpipe drains faster as the water falls further."
-Me

"You are 100% wrong. If the pipe diameter is smaller then it stays full. A full pipe has head pressure. This is so basic, that it can not be overflooked. If you introduce air, then the head pressure disapears."
-Bean

Ok, tested this one out in person. The 1" pipe going through the 1" bulkhead cant develop head pressure...the water is in free fall the whole distance from when it spills over the standpipe, until it exits the bottom. The standpipe is 12" tall, the overflow 15" (tank is 16"high) The most that this setup could take was about 600gph...as the water is much higher in the overflow than the standpipe. Then, with a 2" standpipe, the water was able to spill over the top much easier, so there was no rise in the overflow water level...and then the water spilled through the bottom bulkhead...however...I was able to dial up the pump to over 1000gph and this version kept up. The standpipe in both cases was the same 12" tall. Ive explained it before...but if you have a better reasoning as to why this could or couldnt happen, be my guest.

"A good example, however unlikely, would be a 3/4" standpipe on a 1" bulkhead...no head pressure exists because the water never even builds up enough to gain depth pressure, right?"
-Me

"WRONG!!!! The system will be at full siphon. UNLESS you introduce air. Once the air is introduced, you are no longer working with head, you are working with free fall. AND YES A LARGER PIPE AND BULKHEAD WILL OBVIOUSLY FLOW MORE. Once again this is not a "depth" issue. "
-Bean

Well, thats the whole point I see. You use dursos to make siphons...I dont...its not what they are for. FWIW, anything I say could be applied to regular standpipes w/o a durso if you didnt care about noise. If you use a pipe that is equal to or smaller in diameter than the bulkhead / pipes below it, then you are working with free fall (no head pressure...this contradicts your statement that pipe diameter has no effect on pressure and therefore flow...see...you said it yourself, you just havent made the link). If the pipe diameter is smaller then there is no head pressure, its in free fall, and if anything, making a vacuum as it does so which sucks in the air. Only if you are trying to create a siphon or vacuum on your durso...which I dont think is a good idea for many reasons previously stated.

Then if the pipe diameter is bigger than the bulkhead it drains through, and the flow is boosted (which is the point of doing so) the water builds up inside the pipe above the bulkhead...creating head pressure...until it creates a siphon/vortex and clears. If you had the smaller pipe, 1", then the water backs up on top of the standpipe to create enough pressure to equalize the flow. The thing is that this can overflow a tank...if the larger pipe is used, this point (also the point of greatest restriction) is lower in the overflow and allows water to build up if needed to...but inside the standpipe. And of course its a depth issue! If we had only 1" of depth, then none of this would even be possible...so depth plays a role as far as forcing water through a hole.

"But with a 2" pipe on a 1" bulkhead, this is not the case. In this case the water can drain faster in the 2" part than the 1" part...so head pressure builds up (granted, if the flow is more than the 1" bulkhead could easily pass w/o buildup)."
-Me

"You have just shown that a 2"by1" system will flow more than a 1"by3/" system. Isnt this a givin. Again it has nothing to do with the depth."
-Bean

Sure it has to do with depth...what we are doing by using a larger diameter standpipe than the bulkhead is lowered the most restrictive point in the system to the bulkhead. If we used 1" pipe, then this most restrictive point would be at the top of the pipe...causing water to back up in the overflow higher than with the larger pipe. Of course...if you are restricting you air inlet to help siphon water...this doesnt apply.

"So a good rule would be that if the standpipe is equal to or less than the bulkhead diameter, there is no head pressure"
-Me
"You are again 100% wrong. This is WHERE THERE IS HEAD PRESSURE."
-Bean
How could I be wrong? since the water is in free fall, as you mentioned earlier...there is no chance for water to build up and make head pressure...if anything, the pressure is negative at this point, which is why air gets sucked in.

"To restate what you said above...Head can depend on volume...not enough volume, no head at all. And since it is a ratio with pipe diameter...pipe diameter also has a role in head pressure...too much pipe diameter, no buildup, no pressure...nothing but FREE FALL there it is, LOL!"
-Me
"In that hard to follow statement, you made MY point. A durso is a free fall system so we are not dealing with head. It's that simple. Yes, you could adjust the durso to move water via HEAD, but that is a siphon. Something we don't want."
-Bean
A durso with a 2" standpipe on a 1" bulkhead does involve head that builds up inside the pipe above the bulkhead if the flow is high enough (and this durso would not be a free fall system). With any system, unless the pipes are so large to allow nothing but free falling water inside, we will always have head or vacuum. You experience seems to be with using a durso to make a vacuum...my standpoint is with head pressure...which is not how a siphon is formed...a siphon is formed with a vacuum (if you want to call it head, fine, but then we must make note of negative head and positive). Where it applies here is that we are not talking about free-fall because we are looking at ways of getting the most flow through a given diameter of pipe/bulkhead...so free flow or falling water w/o head or vacuum wont happen.

"I think the reason why you do things like this is something I see you often mentioning...using your durso as a siphon."
-Me

"My durso ...(got it, no reason to repost)

You have to adjust the air in a "durso" to tune it. To much air and you overflow, to little and you siphon. You will see people that have tuning trouble. I can explain why, but that is for a different post."
-Bean

I see. Do you have a photo or something? With a durso, opening the air too much should not result in an overflow. I think that there is something wrong with the setup. Ok, you arent tuning it to siphon...but something isnt right if leaving the air too open results in backing up. It explains your standpoints however. This is not the only way. not to poke fun, but seriously, if you can tell other people how to tune their's right, why cant you get yours so it doesnt back up if the air is left open? IME, the only thing that should happen if the durso's air inlet is too far open, is the possibility of more noise getting out.
 
First of all Herbert I would like to say that I do not have your expertise. My line of work is entirely different from your own. You appear to be very intelligent and I respect your opinions. I will however attempt to describe in layman's terms what I believe is the confusion. Your stand pipe theory assumes a physical limitation is placed on flow. Thus you are analyzing the structure and restrictions of the plumbing itself. Here head would apply. The durso's flow however is not limited by the plumbing, provided that you have indeed sized it correctly. Please make sure you hear that, the durso for our purposes is sized correctly and thus introduces no restrictions on flow. What regulates flow then is the introduction of air, which has nothing to do with the plumbing, provided the plumbing is adequate and has not introduced any restrictions. (About friction loss, friction loss is so insignificant in this context it is not even funny. And in truth I do not even think it applies, seeing that there is no siphon.)
 
Man alive I didn't think the question would start all of this. Well I have one more question hopefully it won't make such a rile with everyone. So I have decided to go with making an overflow so that I can get the water height a little higher in the tank. Anyhow my question is this.

Will using silicone work alright to make an over flow box which will be suspended part way up the tank?

What thickness of acrylic should I use for the overflow? It won't really be out of water very often, at the most it will only be during an occassional large water change, but most of the time it shouldn't even be that way.
 
Ruminari,

Please do not highjack this thread!! :D


I was just scrolling the top of the thread to see if your problem was ever resolved. It seems that you were lost in the shuffle 2 pages ago.
 
I think that nearly everyone will agree that an overflow is better than no overflow. So I am glad that you are considering installing one.

I would go with 3/16" or 1/4" in either glass or Plexi. If you want to have "teeth" then it would be eisier to have them done in Plexi.

Many people report that using silicon to bond between glass and plexi is not the most reliable.
 
You have to adjust the air in a "durso" to tune it. To much air and you overflow, to little and you siphon. You will see people that have tuning trouble. I can explain why, but that is for a different post."

The examples are the 2 possible extremes. A well designed setup will not overflow no matter how much air is allowed in. I think you need to play with horizontal intake and the downturned elbow. You will see that the downturned elbow needs to be there to make the system work with correctly sized plumbing. THe down turned elbow is a siphon. You need to remember that... we introduce the air AFTER the elbow.

I think your on track to understanding why these things work, but you need to really examine what goes on at each step.

Bean
 
Teeth cut down on the skimming ability. I would only use them if the water dept over a FLAT overflow is over a 1/4 or so deep.

My water is less then 1/8 deep on my 75 gallons overflow. I am roughly around 1100gpm. The overflow is 4 feet long.

You are correct, acrylic to glass is tough to do well. Silicone does not stick to acrylic. A 2 part epoxy would be better... or a glass box with an acrylic inset may be better.

If you have the room a full box offset from the tank wall would be ideal. This gives you even more linear overflow.
 
Snap-On,
First of all, let me say that I love your tank. That whole tool-themed sump rocks.

You are right in assuming that I am talking about is different from Bean. That is in a sense, the root of the confusion. I am talking about flow characteristics that happen when we are pushing the maximum potential of a drain system (which is what this thread was about in the first place). Bean is talking about a perfect match between a durso and water flow which is at the other end of the spectrum.

I know what you are saying as far as the introduction of air...but how can that regulate flow? <<< let me rephrase that...I know it can influence a siphon, or cause a drain to back up, or even help create a temporary boost in speed through a partial syphon...but if plumbed properly, a durso's air inlet should do nothing to the maximum throughput of the water. Its just displacement, or allowing for the free flow of air w/o noise. You should be able to run the system without air control (open top standpipe) and get the same results). Water is heavier and so if it needs to drain faster to keep up it will push water out of the way (in a head pressure setup)! This is why head pressure based systems outperform vacuum ones...in a vacuum, water cant displace air as easily because even though its heavier, its higher density/viscocity works against it, and air can more rapidly fill in to a vacuum during free fall. This means that the potential max in a free-fall system will be less than in a system with head pressure (less air is introduced so more water can flow). And if a properly sized durso placed no restrictions on flow, then why does the water rise to the level of the inlet? Because it does raise the restriction point to the top of the pipe...obvious. So how could a durso not be some kind of restriction?

Ok, I can see how...by adjusting the air to not be too little as to allow a siphon to form....yet keep it closed enough to what?!? Only to prevent noise as far as I can tell. How could properly adjusting the air aid in the throughput/ alleviate the restriction of the durso unless some kind of siphon was taking place? Sure, it could be part air and part water...but its still a suction and therfore a siphon. And a siphon is no way to reliably boost the throughput of an overflow. Eventually it will speed up and purge the drainpipe...and then it could back up if your drain tail is submerged in the sump (many do this to cut down on splashing), and the overflow has lost its boost. The fact that Bean has his overflow to compensate for this when it happens shows how irregular this vacuum is.

A durso shouldnt have to be 'dialed-in' to raise its flow. It should allow only gravity to pull the water down in a free-fall in the pipe...no vacuum that causes the pipe to suck in any more water...just air. Otherwise you are voiding the whole purpose of a durso...to muzzle noise. A durso should function the same with the top T and elbow removed (besides the noise)...not like a carlson surge device. Something tells me that Bean's setup goes through this cycling, but he just doesnt notice because he uses a larger drainpipe than the bulkhead which is more accomidating. But if he ran 1" bulkheads with 1" pipe, it would be a different story...his overflow would most likely binge & purge and gurgle like mad. The only way to know for sure is to see a pic.
 
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