Different sized overflow holes

[Ross B Reef'n]

My new custom aquarium from GlassCages has 3 holes in the overflow. Two of the holes are 2in. The hole in the center is 2-1/2in.

What's the reason for the different sized hole in the center?

 

[JoshH]

Do you happen to have a picture of the overflow? My guess would be it's an emergency drain and the bigger size will ensure it can handle any flow it needs to...

 

[homer1475]

Depends on the type of overflow really. The larger center hole could be for the returns. A picture is worth a thousand words.

 

[W1ngz]

Probably as the emergency drain. The other two are for the primary siphon line and the secondary open channel. The emergency, for absolute safety, would be able to handle all of the flow from the other two if ever both were blocked.
You'd have to ask them for a truly definitive answer why they did it, but I can't see it being any other reason.

 

[Eagle_Steve]

My new custom aquarium from GlassCages has 3 holes in the overflow. Two of the holes are 2in. The hole in the center is 2-1/2in.

What's the reason for the different sized hole in the center?

Normally Glass Cages drills for one large emergency a normal drain and then a return. The 2.5" would be the emergency and the 2" would be the full siphon drain and the return.

 

[W1ngz]

You don't mention if this is a corner overflow or an external, which could change the answer.

 

[Ross B Reef'n]

Do you happen to have a picture of the overflow? My guess would be it's an emergency drain and the bigger size will ensure it can handle any flow it needs to...

Not on hand, I can take one after work.

 

[Ross B Reef'n]

You don't mention if this is a corner overflow or an external, which could change the answer.

Glass box, centered on the back wall

 

[homer1475]

Bottom drilled or side drilled? Basically is it a full tower style overflow or small box type?

 

[Ross B Reef'n]

Bottom drilled or side drilled? Basically is it a full tower style overflow or small box type?

Bottom drilled, full tower

 

[homer1475]

Then the larger hole(assuming it is in the center of the other 2?) is for your returns.

A herbie style overflow.

 

[Ross B Reef'n]

Unfortunately this picture has the cover on the overflow, but hopefully gives a visual reference.

 

[homer1475]

Yup exactly as my SCA tank. Except I have 3 1" holes. I used the center for the returns with a T so the returns come out both sides of the overflow. I would plumb yours the same.

 

[Ross B Reef'n]

Then the larger hole(assuming it is in the center of the other 2?) is for your returns.

A herbie style overflow.

Yes, the larger hole is between the two smaller holes.

Thank you all for the help! This system is definitely "next level" for me.

 

[homer1475]

My tower overflow has 2 large holes on either side of the top of the overflow, just under the weir teeth. This is how my returns come back to the tank.

 

[homer1475]

This is super old photo, but gives you an idea.

I have 2 pies on either side of the T. One is a primary siphon, the other is the emergency. Just google GMAC herbie overflow. It will provide you with all the information to plumb up that tank for the herbie style overflow.

 

[Ross B Reef'n]

2-1/2in seems huge for a return! Hopefully the sicce 4.0 at 4-5 turnover can push through that big of a pipe!

 

[homer1475]

Agreed!

Might want to use it as the emergency, then use one of the other 2" as the returns.

 

[Ross B Reef'n]

I'm also planning to use relays / float switches to shut off the return pump. Redundancy, redundancy, redundancy!

 

[Aquavaj]

Are you sure it's 2" and 2 ¹/²" and not 1" and 1.5"? The bulkheads in the pic look too small to be that big. Of course the tank might just be that big that it's making the bulkheads look small.