Overflow Flow Rate Problems

[Ruminari]

Lets start with a little background. Tank is a 37 gallon flowing down into a 10 gallon sump. The tank is drilled about 6" down from the top of the tank with a 1" drainline and has a durso installed so it drains down 2". The return is routed through a Mag 7 pump which should be putting out somewhere around 400 gph back to the tank.

Our problem. For some reason the overflow line is not able to handle the 400 gph flow rate. Any ideas? We have tried using an adjustable hole cap on the durso top, however that hasn't seemed to help. The only thing that really semi works is completely closing off the durso pipe hole. However this causes the water to fall too far.

Here are some pictures of what we have got setup.

Here is a picture of the durso inside of the tank.




Here is a picture of the outside of the drain line.

[Herbert T. Kornfeld]

Your flow is dictated by the size of the hole at a given depth. The depth of your 1" hole is close to the surface, if not right there...so your max flow will be less than 300gph. What you want to do is cut some acrylic to make a small box, then silicone the box over the bulkhead to make an overflow. That should get you a good 300-600gph capacity.

[Ruminari]

Thanks for the info Herbert, that is kinda what I was hoping that I wouldn't have to do as I don't have access to a tablesaw to cut acrylic with currently. Maybe I'll see how much it would cost just to have the acrylic shop cut it to size for me. Do you think that silicone would be capable of holding up a small overflow box onto the glass even if the water level is below the acrylic box? (Ex: during a water change)

[ChrisRD]

Sounds like you've got more than enough capacity when you cut-off the air to the Durso. I'd try installing a needle valve to allow for more precise air intake adjustment.

[Herbert T. Kornfeld]

Well, also, due to the fact that you are running a durso in the tank w/o a box, you arent even skimming the surface like you should. You could re-plumb it a little different...and reduce your overflow rate to less than 200gph (slow the sump down and use a closed loop / in tank circulation pumps/powereheads)...that way you could avoid having to make a box.

[Ruminari]

An update. I remade the durso and lowered it a couple more inches. It didn't make much of a difference in flow rate unfortunately as the water still raised right up to the very top of the tank.

ChrisRD - where would be a good place to look for a needle valve? Hardware in the brass plumbing section?

Herbert - I was really trying to keep any other pumps out of the main tank and just run with the single mag 7, however that is definitely another option. I installed a ball valve after the pump yesterday before I made this post so that I could throttle back the flow, however I really really have to throttle back the flow in order for the overflow to keep up with the line.

[wave_happy]

You may want to restrict the flow at the outlet of the drain (the end that goes into the sump). Without a slight restriction, a full siphon may not be able to form. It may seem counter intuitive at first, but give it a try.

[Ruminari]

Next update. I took a page from my megaflow overflow kit in my AGA reef ready tank and drilled holes in the side of the durso. This seems to have fixed the problem as it is letting plenty of flow down the pipe now and she's a wisper quiet tank now. I'll keep you guys posted if I have any further problems.

[kimche']

ps...never, ever use brass or copper in your system. Unless you want to kill almost everything in your tank.

[Ruminari]

kimche' - that is definitely true, however I was only planning to use that as an air valve so it wouldn't have any connection to the water whatsoever.

[leaffish75]

Ruminari - i did the same thing you did but i have the internal overflow box

I still only get about 200 gph. I even tried going from 1" to a 1.25" durso. a street 90 on the inside and the rest of the durso on the outside. my QO1200 is out doing the overflow still. One thing to try is get rid of the pvc and replace it with flex spa hose. i get a little more flow once i got rid of my 90's on the.

[BeanAnimal]

Herbert:

THis ceases to amaze me... the flow of the setup in the picture at the top if this thread HAS NOTHING to do with the placement of the bulkhead or it's distance from the surface. You continue insist that this is the case!

The flow of the above "system" is a function of the size of pipe, distance to the sump and the amount of air that can enter the system. You inisist on treating this type of overflow with "static head" flow model. IT DOES NOT FIT.


Bean

[BeanAnimal]

You NEVER want to restrict the flow of your drain system. Tuning your overflow like this is asking for a flood. As somebody already mentioned, yout overlfow is fully capable of keeping up when it is used as a full siphon. If you add a needle valve, you can fine tune the amount of air that is sucked in with the water. You will be able to get the water level just where you want it. You should have some kind of box built around the standpipe (as herbert stated). The overflow box will allow the surface scum to get drawn off into your sump.

Bean

[BeanAnimal]

john guest valves make good air controlds for standpipes. I glue caps on the standpipes then tap and thread them for a 1/4 john gust valve.

[Ruminari]

BeanAnimal - not a bad idea with the 1/4" JG. Now if they just made a gate valve that size.

[BeanAnimal]

I just use the ball valve type. JG on one side NPT on the other. I have a tap, but you could use a steel or brass fitting to cut the threads.

I add a hose to the other end and curl it back over and clamp it at a level just below the overflow or max water height I ever want in the tank. If the water rise up to the hose, it will get sucked in and block the air. This will cause a full siphon to start and drain the water down to the inlet of the standpipe, preventing a flood.

Bean

[kgross]

Personally I think with this setup one of the biggest problems you have is with the screen on the intake, it restricts the flow a lot. If you remove the screen even without your extra holes will it work?

Also Bean, there is some had pressure created if the duroso is made correctly. If your read the site the duroso pipe should be one size larger than the size of the bulkhead. This allows water to build up inside of the pipe to create more headpressure agains the small bulkhead. Even without a larger standpipe the restriction caused by the change from the standpipe to the bulkhead will cause some water to build upside of the pipe allowing for more waterflow with a deeper bulkhead than with a shallow bulkhead. If the pipe is the same size there is only a small amount of head created, but if the duroso is created correctly you can have up to the full height of water as head pressure to flow a lot more through the bulkhead.

Kim

[cateyes]

can someone please tell me the difference between a "standpipe" and a "durso"???? every time i think i understand i read something that confuses me....
thanks a lot,,,lisa

[BeanAnimal]

Kim without creating another huge thread with a lot of bad information. Pipe Diameter has NOTHING AT ALL to do with head pressure. This is the first thing you learn when dealing with fluid or "head pressures" A 40 foot diamter pipe with a 1" diamter hole in the bottom will not push the water through any faster than a 2" diamter pipe with a 1" hole in the bottom.

Not trying to flame your post, but it is almost 100% wrong. The size of the hole on the bulkhead or the smallest diamter section of pipe is the limiting factor in a full siphon situation (vertical drop remaining thehte same).


Also regarding the screen... you are correct that the system will flow more without a screen. BUT if they system can keep up fully submerged with a screen and without air input (a full siphon) then it can be fine tuned to not gurgle by draining to low. You are reducing the volume from the full siphon.


Bean

[kgross]

Bean,

I never said that the pipe diameter created head pressure. I said that a duroso stand pipe will create a colum of water above the bulkhead (IE head pressure) allowing a larger flow of water through the bulkhead. If the size of the stand pipe is larger than the bulkhead, the bulkhead will limit flow, If the stand pipe is 20 inches high, without creating a siphon you can put 20 inches of head pressure on the bulkhead putting much more than 300 gph through the bulkhead. If the standpipe is to small you will create a siphon and a lot of noise when trying to do this same thing. That is why a duroso standpipe has to be larger than the size of the bulkhead to work correctly and quitely. If the bulkhead is lower than the waters surface and you use the correct larger sized pipe the height of the water above the bulkhead will effect the flow through the bulkhead. The lower the bulkhead is the more flow you can get through the standpipe setup if it is built as Richard has defined on his web site

As to the difference between a stand pipe and a durso, A durso is a type of a stand pipe that is designed to be quite. It uses a down turned elbow to stop the sound of the water falling, with an air hole to stop a siphon from forming. A normal standpipe is just a piece of pipe going from your bulkhead to the top of the water. To see more of how a durso works check out his web site.
www.dursostandpipes.com

Bean, if you still do not understand how the water height above the bulkhead effects flow I will try and draw you some pictures so you can see the head pressure in the plumbing.

Kim

[BeanAnimal]

Kim I fully understand how water height effects the flow of various types of drains or standpipes. What you don't understand is that moving the bulkhead up or down in relation to the elbow makes no difference. The water is still moving the same vertical distance weather it does so inside or outside the tank. The larger pipe outside the tank REDUCES the velocity of the water by allowing the air to mix with it. The air is being introduced at the TOP, not part way down the back side, there is no "Head Pressure" the way you describe it. This is more or less a free fall.

That said, if the air was introduced part way down, presumably on the back side of the tank at the elbow, then you could measure the head pressure. The water between the down turned elbow and air inject point will be a fill siphon. Following the "durso" design, the next section of pipe will be larger than the siphon section. In other words the water will free fall. In this scenario, you will not have as much control of the siphon via the air that is being injected into the system. You may get be able to get more flow due to the head pressure, but you will have much less control. You will also have more noise due to the added velocity produced by the head pressure. The point begs the question, why not add more standpipes or use larger bulkheads/plumbing instead of trying to shove to much water through a small pipe.

NOW lets go back to the original picture and question. The setup was fully capable of keeping up undr full siphon. This means it could be adjusted by reducing the flow with an air valve.

Bean

[Herbert T. Kornfeld]

I'll stick to math Bean. I really dont care to redo our old thread...its simple and everyone knows that depth/pressure is a huge factor in flow through a bulkhead. The overflow rate has very little to do with the length of the downspout/drain pipe. My experiments, experience, and research back that up. If anyone cares to see what Bean is talking about, go here: http://archive.reefcentral.com/forum...5&pagenumber=1

Also, as you can see, others are finding better results by using larger diameter durso's to eliminate the vacuum that can benefit an overflow one minute, and back it up the next (and the extra noise it makes is a PITA!). A vacuum is not a reliable way to speed up an overflow...only extra pressure from depth is. The free flow of water through a hole at a given depth is the only reliable way to determine a consistant flow. For a vertical drilled hole, the flow calculations for flow are as follows:

.5" .75" 1" 1.5" 2"
0.5 59.9 134.7 239 538.85 957.97
0.75 73.3 164.9 293.3 659.9 1173.27
1 84.67 190.5 338.6 762 1354.77
1.5 103.7 233.3 414.8 933 1659.2
2 119.7 269 478 1077 1915.9
3 146.6 329.9 586 1319 2346
4 169 381 677 1524 2709
5 426 757 1704

The left column is the depth of the hole in inches, and the top row is the bulkhead diameter. The depth of the hole reflects the amount of water covering the hole as well...so a 1" bulkhead at .5" depth means that the watersurface is at the middle of the hole. As you can see, with depth, the flow rate increases. As you go deeper in water, pressure increases...just like if you were to drill a 1/4" hole towards the bottom of your aquarium...it would shoot across the room, but if you drilled the hole an inch from the water surface, it might just trickle. Keep this in mind. The closer to the surface you make your overflow, the larger diameter opening you need to compensate or the water level will rise until the pressure helps it equalize. This is why people have overflow boxes...its like having a long wide opening for water to flow over and maintain a low water level. Then, down in the box you can have your bulkhead where it can build up a good few inches of pressure (if needed) to help with the flow. What you have done Ruminari is extended your opening to the top, but not enlarged it...so to run 400gph through it, the water will have to rise 1.5"...no longer skimming the surface, and possibly overflowing your tank. You either need to enlarge the intake by increasing the diameter of the intake, or the more effective solution would be to add the box. Otherwise, if you want to keep the 1" inlet and still skim the surface...at a reasonable depth...you will have to decrease your overflow rate under 200gph, and to keep the intake screen, you will have to reduce it even further. In order to keep the standpipe as your overflow, you would need to use reducing connectors to add a piece of at least 1/5" PVC as your intake...if not 2" with mesh/screen guard.

kgross, Bean is right with regards to your post (i think, but from the 3rd person, I can see many people arent being descriptive enough and you both could be interpreted wrong even though you may agree on the same things and both be right). Or maybe you are right...I cant make out what either of you is trying to say...I read one post...go back to another...then go back to interpret things differently...I see half things that are right, and then some things that are very wrong. You are sort of right in that a larger diameter durso COULD increase the flow through the bulkhead below it...if nothing other than because you have increased not the pipe diameter, but the size of the opening at its inlet which is the weakest link. If the flow increases beyond a certain point where the durso becomes submerged...then Bean is right...because then the 1" bulkhead becomes the bottleneck. Having a larger diameter drain-pipe but the same diameter bulkhead will do nothing for increasing his flow...the point that counts is where the intake is...which in this case is not the bulkhead, but the pipe he has added on to it going up to the surface. OTOH, it would help if the pipe that is inside the tank were of larger diameter...increasing the linear overflow area like a box would. If the pipe were 3/4", and the bulkhead 1", then increasing the diameter would help, but being that the pipe in the tank through to the bulkhead is the bottleneck...no increase in the pipe diameter once it passes the bulkhead will help increase the flow...although it does make for excellent sound muzzling. So, long story short, I think what Bean meant to say is that a 40ft long 1" pipe with a 1" hole in the top will flow no better than a 40ft 2" pipe with a 1" hole in the top. But, a 1" hole in the bottom of a 5' long pipe will flow much slower than the same hole in the bottom of a 40' pipe.

[BeanAnimal]

Kim..

I just re-read your post and need to add something to my previous post.

You assumption is that the small bulkhead with the large pipe stacked on it is what creates the head pressure. That would be true if the air were not being added. But then that would mean that we would be at full siphon again. There would be no adjustment other than the size of the hole.

I just read richards site for the first time and he states that he is not even sure why the larger pipe works with a smaller bulkhead so well. The smaller bulkhead does allow the water to back up slighty then get sucked through. This slows the velocity of the water down. Somewhat the same as rip-rap in a spill way. He also states that on larger bulkheads there is no nead. This is simply due to the fact that there is so much air and cross section that the water does not slow down.

Bean

[Herbert T. Kornfeld]

"I just read richards site for the first time and he states that he is not even sure why the larger pipe works with a smaller bulkhead so well." - Bean

It isnt whats going on at the bulkhead...by making the durso parts larger, you are making sure that the durso's intake isnt the bottleneck anymore...the bulkhead is. This is what Ive been trying to tell you since we first met. By increasing the durso, its intake is no longer the same as the bulkhead's...its larger...enough that the flow calculations can be done from the depth of the bulkhead, not the durso's intake. This is why a deeper overflow box will always outperform a shallow one if plumbed right. Trust me for once...you'll see. Im actually shocked that richards couldnt come up with the reason...its simple. Thats it, Im going to have to write a story with all the info for a future issue of reefkeeping mag.

[kgross]

Originally posted by BeanAnimal
Kim I fully understand how water height effects the flow of various types of drains or standpipes. What you don't understand is that moving the bulkhead up or down in relation to the elbow makes no difference. The water is still moving the same vertical distance weather it does so inside or outside the tank. The larger pipe outside the tank REDUCES the velocity of the water by allowing the air to mix with it. The air is being introduced at the TOP, not part way down the back side, there is no "Head Pressure" the way you describe it. This is more or less a free fall.

You are still wrong, moving the bulkhead up or down in releation to the elbow will effect flow. If the pipe is larger diameter than the bulkhead as a durso needs, the air will not fill up the pipe breaking any siphon in the pipe itself, it will only stop a siphon from creating that siphons from the down elbow all the way down the stand pipe.

First the pipe outside of the tank that you are talking about does not introduce air to the pipe, if it did, it would only serve to break a siphon from the bulkhead down, which would slow down the flow since if you have a siphon though the pipe up the standpipe to the T you will have a lot of "head sucking the water down the pipe (with head pressure negitive pressure works the same as positive only in a different direction.

With the lower velocity of the water in the stand pipe the water level below the introduced air will build up above the bulkhead, when this water level builds up in the stand pipe it creates more head pressure than when the water level does not build up.

That said, if the air was introduced part way down, presumably on the back side of the tank at the elbow, then you could measure the head pressure. The water between the down turned elbow and air inject point will be a fill siphon. Following the "durso" design, the next section of pipe will be larger than the siphon section. In other words the water will free fall. In this scenario, you will not have as much control of the siphon via the air that is being injected into the system. You may get be able to get more flow due to the head pressure, but you will have much less control. You will also have more noise due to the added velocity produced by the head pressure. The point begs the question, why not add more standpipes or use larger bulkheads/plumbing instead of trying to shove to much water through a small pipe.

NOW lets go back to the original picture and question. The setup was fully capable of keeping up undr full siphon. This means it could be adjusted by reducing the flow with an air valve.

Bean

The whole idea of the durso is not to use a siphon to keep up with water flow, since a full siphon of the standpipe will cause extra noise since with the down turned elbow the siphon will draw the water level down (unless the pipe is to small to safely handle the flow) and the system will flush making a lot of noise. If noise is not an issue, just use a straight standpipe that goes up to the water, you will get more flow though it than with the extra elbows on it. To make the durso work correctly you need to size the pipe large enough that it does not try to siphon, instead you can use it to create head pressure above the bulkhead and get more flow through the bulkhead.

Kim