How close is too close for drilling holes?

[Blazer88]

Here is the situation, below is a picture of a tank that is for sale and it already has a hole drilled into the side. I am wanting to drill two more holes for 1" bulkheads so I can do a coast-to-coast overflow. Would it be ok to drill two more holes just below the plastic trim on this side? I'm worried the holes would be too close together and would significantly weaken the glass. I would use the hole that is already there for a closed loop. I have been wanting to start a 120 and I'm hoping I can make this one work. Thanks for any input.

Tank for sale:

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What I want to add to the same side:

 

[Reefdaddy1]

I would not recomend it that close, I would use that hole for a closed loop, Make 2 more holes above and to the right. this way after all the PVC is installed you have no room conflict. Meaning your PVC from the established hole will not be in conflict with your Overflow hole. If you get what I mean. Here is a pic

 

[Blazer88]

Ah, the pics really helps out. Is there any reason I wouldn't still be able have the overflow as a coast to coast? Do you think three holes in the side of the tank would be too many? I would hate to find out the hard way once I start to fill it, lol. Thanks for your help.

 

[Reefdaddy1]

Coast to Coast meaning from one to end to the other or on the side.

 

[dnjan]

First, I still think that two 1" bulkheads are too small.

That said, the problem you will have with a normal coast-to-coast is that the bulkhead for your closed-loop will probably stick up an inch or so above the top of the hole already drilled. And, from your drawing, it looks like there is actually only about 4 inches between the bottom of the tank molding and the top of the existing hole. Subtract 1" for the bulkhead mentioned above, and an additional 1/4" for the thickness of the plexi on the bottom of your coast-to-coast, and you have only 2-3/4" for the overflow bulkhead to fit in. Probably too tight, even if you could get the holes located perfectly.

You could try to make a stepped drain box that went up above the closed-loop bulkhead ...

 

[Blazer88]

I think I would rather spend the extra money in the beginning and do it right the first time. I would rather have the intake for the closed loop lower (and possibly two of them rather than one) and enough room for 1.5" bulkheads for the overflow. The guy still wants $270 for the tank which I think is too much for a used tank. I'll probably just get a new tank and do it right.

 

[Scooterman]

I got an Oceanic 60g New for just over a $100!
I agree save the headache, do it right, get another tank to do what your asking.
JMO!

 

[Detri]

Well rule of thumb is, You should be as far from the edge/top/side of the glass/hole as the size of the hole you are drilling. If you are drilling a 2" hole you should be 2" from the edge of the glass or another hole.

As long as you are putting and overflow in the tank. you are taking the pressure off the glass that is drilled. So it won't be a huge issue. But, that said, put as few holes in the glass as you need to. Meaning, if you can get away with 2 drains and just 2 returns for your closed loop and 1 closed loop intake then that is all I would put in.

The length x Height of the pane you are drilling has a lot to do with it too. If it looks to cramped. Then it Likely is.

 

[dnjan]

As long as you are putting and overflow in the tank. you are taking the pressure off the glass that is drilled.

The presure reduction from putting an overflow like shown in the previous picture is less than 0.1 psi.

The issue with holes near the top of the tank is not pressure on the glass, but rather bending stresses on the glass from pressures at lower depths. The water is pushing sideways on the glass, and the glass is just held in place at the edges. With that in mind, holes close to an edge (I agree to stay at least one hole diameter away from the edge) are much less of a problem than holes in the center third.

 

[Detri]

The presure reduction from putting an overflow like shown in the previous picture is less than 0.1 psi.

The issue with holes near the top of the tank is not pressure on the glass, but rather bending stresses on the glass from pressures at lower depths. The water is pushing sideways on the glass, and the glass is just held in place at the edges. With that in mind, holes close to an edge (I agree to stay at least one hole diameter away from the edge) are much less of a problem than holes in the center third.

I meant an overflow as shown in Post #1 and Pic 2. With the bottom of the overflow attached to the glass that is drilled it takes a lot of stress off the holes and that pane of glass.

 

[dnjan]

In my experience, most people retrofit overflows like that using silicone sealer as the adhesive. Silicone is very flexible compared to glass, and I doubt it will have much effect in reducing stress when used to connect (also relatively flexible) plexiglas to glass.

Plus, there is the potential for added stress from the bulkhead if rigid PVC is used (as in the picture). I prefer using spaflex instead of rigid where any pressure on the pipe could result in stresses on the glass due to pushing/pulling on the bulkhead.