Overflow hole size help

[Darsh85]

Quick question please.
I'm planning an exterior bean animal overflow box coming from a c2c.
The pipes will be 3x 3/4" or 1" I'm not sure which will be better (30g DT with 20g sump) I want approx 200gph.

I have to buy a diamond hole saw and they're pretty pricey, so I need to know how big a hole I need going from tank to overflow box.
Also, I'm a little nervous about drilling so I just want to do it one time, so how big of a hole, or should I say, how big does my bulkhead need to be to comfortably allow enough water through???

Thanks

 

[mcgyvr]

3/4 should be just fine for that size tank..
The diameter of the hole depends on which bulkhead you get.. (It is NOT a 3/4" hole)
Typically thats stated in the description of where you buy it from

 

[Darsh85]

3/4 should be just fine for that size tank..
The diameter of the hole depends on which bulkhead you get.. (It is NOT a 3/4" hole)
Typically thats stated in the description of where you buy it from

Thanks. Yes I know but my question is, if the bean animal syphon is 3/4" how big should the bulkhead be going from the tank to the box before the syphon to ensure enough flow can make it to the box?

 

[lapin]

Actually there IS an exact amount of water that will flow through a 3/4" bulkhead. Unfortunately - it's very hard to calculate without knowing EVERYTHING about the installation and set up.
Even then - calculating and actual real life flow rates rarely if ever match up exactly. But a 3/4" will flow an exact amount once it's installed. Exact for whatever increment of time you choose.
So ...... averages are used often as you mentioned.
Normally folks use rule of thumbs - which can be dangerous too.
A 1" bulkhead will normally flow 700 gph in most of our installations. That can go plus/minus 100 gph depending on installation/application.
Two 1" can handle 1400 gph
A single 2" bulkhead can handle more than two 1"
The reason is square inch area of the internal pipe. This is what contributes to how much water can flow inside it - along with the head pressure above plus the affects of gravity and air venting.
Square area of various pipe sizes ( pi r squared )
2" pipe = 3.14 square inches of area
1" pipe = .785 square inches of area
3/4" pipe = .44 square inches of area

 

[mcgyvr]

Thanks. Yes I know but my question is, if the bean animal syphon is 3/4" how big should the bulkhead be going from the tank to the box before the syphon to ensure enough flow can make it to the box?

Sorry...I didnt pay attention here..
I would probably use 2 x 1" bulkheads from tank to external box...

 

[Darsh85]

Sorry...I didnt pay attention here..
I would probably use 2 x 1" bulkheads from tank to external box...

Okay thanks again haha but I'd prefer to drill one hole and be done with it. I think a 1.5" bulkhead would be enough. The bigger the hole saw the higher the price

 

[Darsh85]

Actually there IS an exact amount of water that will flow through a 3/4" bulkhead. Unfortunately - it's very hard to calculate without knowing EVERYTHING about the installation and set up.
Even then - calculating and actual real life flow rates rarely if ever match up exactly. But a 3/4" will flow an exact amount once it's installed. Exact for whatever increment of time you choose.
So ...... averages are used often as you mentioned.
Normally folks use rule of thumbs - which can be dangerous too.
A 1" bulkhead will normally flow 700 gph in most of our installations. That can go plus/minus 100 gph depending on installation/application.
Two 1" can handle 1400 gph
A single 2" bulkhead can handle more than two 1"
The reason is square inch area of the internal pipe. This is what contributes to how much water can flow inside it - along with the head pressure above plus the affects of gravity and air venting.
Square area of various pipe sizes ( pi r squared )
2" pipe = 3.14 square inches of area
1" pipe = .785 square inches of area
3/4" pipe = .44 square inches of area

Thanks a lot! I was pretty sure I heard that before so I was thinking a 2" would be too much. I think I'll go for the 1.5"

 

[laverda]

Two 1" bulkheads will be better for this application. A 1.5" requires a big hole that can not be to close to the edge of the glass and may force you to move your overflow lower than desired to clear the bulkhead. 2
smaller bulkheads will be better structurally and provide plenty of flow. Also with only one bulkhead you may find either box rotating or tilting a bit.

 

[Darsh85]

Two 1" bulkheads will be better for this application. A 1.5" requires a big hole that can not be to close to the edge of the glass and may force you to move your overflow lower than desired to clear the bulkhead. 2
smaller bulkheads will be better structurally and provide plenty of flow. Also with only one bulkhead you may find either box rotating or tilting a bit.

Yes you make some good points actually, I'll have to some measuring and make a decision. I know 2 holes will be better, but that means double the stress of drilling haha. Thanks

 

[FlatBrokeMedic]

Actually if you look on amazon or eBay you can find glass hole saws for about 10 to 15 dollars