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