Dual overflow question

[mightytexn]

My tank is currently drilled in the back upper corner for my overflow, with a screen on a PVC elbow that allows the water to drain into my sump. This overflow is loud, mostly due to poor design since I knew nothing when I did it originally. I am going to build a new stand for the tank and that is going to require some changes to the overflow plumbing because of an increased stand height. I was wondering if I could do a smallish diameter (1/2"-3/4") overflow like these https://forums.saltwaterfish.com/t/288154/diy-overflow-check-it-out and just have my existing drilled overflow as a backup to take whatever the smaller one can't handle. My theory is that since the siphon overflows require 70-100% of their rate to be returned to the tank, if my return is approx 110-125% of what a small diameter siphon will handle, the siphon should work perfectly and the drilled overflow with handle the small amount that is left over silently. Someone please let me know if I'm way off base and going to flood my sons room before I start this in a couple days.

 

[posiden]

Hello,
I don't believe you are way off base. It sounds real similar to what I am building. Only I will have three pipes for my drains. The first two setup like what you are saying and the third for an emergency. Instead of doing the design you posted I will be doing durso or stockman style drain pipes. But I have a OF. It doesn't sound like you do.
You could create a coast to coast OF and plumb this style of drain into it. That is what I have planned for my 75 in wall. I have the tank and it is drilled but I haven't built the OF yet for it. This is BeanAnimal's design.
How far down are your tanks holes? Do you have a pic? Is the tank in operation? I would assume no on my last question since you will be building a new stand.
Here is a pic of mine. It is on a 20L. This is a version of the design. The fourth bulk head is for my return.
From left to right, Open channel, Full siphon, Emergency, Return.

A view from the back

 

[mightytexn]

Thanks for the reply. The tank is up and running right now. I am building the new stand for it because the metal one it came with is showing a little bit of rust and I don't want it to come crashing down eventually. The hole in the tank is in the top right corner about 3 inches in and 3 inches down. Here is an old picture

I don't want to build an overflow box like you have since the tank is up and running and that would require breaking it down while the silicone dried. As long as the small siphon overflow should handle most of the water, and the existing will handle all the excess I think I'm good to go.

 

[posiden]

Well, in that case I think you are correct. You will need to build one like the one you have linked to as you will be going over the top. I don't have any experience with that design but they say it is pretty reliable at getting the flow started again in an event.
Good Luck.

JMO, I don't know that I would rely on the math to configure the drain size. I would build it bigger, and put a ball valve on it to restrict flow. This way it would be able to be tuned.

 

[mightytexn]

Alright thanks for the input. The stand is being built in the next couple of days and after it is waterproofed I'll be building the second overflow.