Overflow Question

[maxima k2]

I am having a problem with the overflows on my tank. I am using 2-3/4 bulkheads and 2- 1in bulkheads and am unable to let my little giant 4mdq-sc run at full flow I have to use a ball valve to reduce flow. All the bulkheads are using external Dursos, I used the RC calculator to determin the size originally. The calculator gave me an inch and a half I went with 2 1" bulkheads and I came up short. I added the 2- 3/4" and still cannot open the valve more than three quarters with out overflowing my tank. I need to know what size to upgrade to and how many.

[kgross]

Tell me more about the tank. Do you have an overflow installed? Is it drilled on the bottom or back? how do you have the durso setup? if you remove the top of the durso does it flow enough? Currently my tank has a 1 inch bulkhead and it is handling around 1500 to 2000 gph, so you have enough space just sounds like you don't have enough head pressure on your bulkheads or you have some restrictions.


KIm

[Zoanthus]

^

[maxima k2]

Sorry I should have given more info. All the bulkheads are on the back about a half inch from the top. I do not have an overflow box I am just using strainers on the bulkheads. Water passes through the bulkhead into an extenal durso, then down to a 1 inch flex tubing, then into the sump.
The flow is the same with or without the caps on the durso. All the dursos are larger diameter than the bulkheads.
As far as head pressure, I do not know how to increase it. If you have any ideas please let me know.

[KevinM]

You have discovered the one caveat of mounting your bulkheads high in the tank. There is no way to increase flow through those BHs. Flow through an opening is partly determined by how much water is "stacked" above it (or "head pressure", if you will).
The only way to get more flow through that tank is to add more bulkheads, or increase the size of the ones you have.

Kev

[webpolk]

Can't you also just mount an overflow box inside the tank that will help build pressure inside the box?

Steve

[FJ40]

So, if you were to drill the back of your tank, how far below the water surface is a good place to drill to have adequate head pressure?

[maxima k2]

Now that I know that, what size bulkhead should I upgrage to? I need to fix it asap I don't want to burn out my pump.

[kgross]

First running the valve on the pump will not burn it up. As to what size, it sounds like you need more so I would say first increase the 2 3/4 bulkheads to 1 inch and see what that does, next add more 1 inch until it can keep up. Or install a small overflow and drill your next hole at the bottom of the overflow and you will be able to put a lot more flow through it.

Kim

[shawn maybee]

did you drill a hole in the top of the durso so the air and help suck the water through fast ? just a thought ,,wiht a hole drilled into the durso it might increase the flow a little bit ,,let me know how it works

[maxima k2]

I do have holes drilled in the top of the Dursos, but it doesn't seem to matter. I can take the caps entirely off and they still run the same. I am going to replace the 3/4 inch bulkheads with 1.5 inch and see what happens. I guess there is no rule of thumb to go by when putting them at the top of the tank. I think enlarging the existing holes would be better than drilling more, I don't need anymore hoses running into the sump. BTW what size Durso should I make 1.5 or 2 inch?

[pr0nd3xtr]

I think the smaller the hole, the faster they will run. Try placing something over the holes and see if you get more flow. I can run my 4mdqx-sc wide open with a single 1-1/4" durso and a 1 inch BH.

[maxima k2]

I have tried that idea but may give it another shot, I am curious is your tank drilled in the bottom or in the back? I am going with 1.5 inch bulkheads in place of the .75 . I am out of ideas.

[otolith]

Before putting in larger bulkheads, why don't you try taking off the durso's and see if that changes flow. You may find that you won't even need durso's. Graham's tank (April ToTM) uses 2, 3/4" overflows like you've installed, and pushes around 600gph. I would think you'd be able to get double that with the current setup, and should easily handle the little giant. You may find that you don't even need the durso's with this setup.
HTH,
Derek

[maxima k2]

I appreciate the advice but I started without dursos and it did flow a little more water. BUT the noise from the bulkheads was unbarable I had to leave the room in order to talk to some one. That is when some one told me to switch to durso set up. It doesn't flow as well but it sure is quiet. I have already ordered the bulkheads, if I can't find another way I am left with putting larger ones in and HOPEFULLY fix the problem. I just cant see running a pump and having to throttle it back when I bought it for the flowrates. Maybe I am just crazy(which is very possible)