Bulkheads on bottom

[Cosmo]

Anyone drilled bulkheads into the bottom of an acrylic tank before?

I'm seriously contemplating putting two drains on the bottom and am curious if anyone has tried and run into problems?

Jim

[Tropical Haven]

You shouldn't have any problems at all. I put all my bulkheads on the back glass instead of the bottom because there is greater pressure on the bottom of the glass compared to the sides.

[Cosmo]

Scott,

That's my thought as well, the pressure that is. I have numerous bulkheads on the sides but have never put them on the bottom before.

Plus, I don't know how integral the bottom piece is the the overall integrity of an acrylic tank :confused:

Jim

[Graham]

While I haven't done it on an acrylic tank, My 175 is drilled in 4 spots on the bottom and I currently use two of them....years ago it was set up as a reverse flow UG. There should be no problem drilling your tank, just make sure that the bottom is supported

I've also drilled a 220 gallon with out any problems.

G

[kaceyo]

I had the bottom drilled on my 75g reef tank years ago and never had any problems at all. I didn't do it myself tho, had a pro do it.

Kacey

[Tropical Haven]

Drilling the bottom is fine and I have done it myself but I started doing the sides instead just for the reason I gave above.

[Cosmo]

Thanks all :)

[Graham]

Just a warning for anyone thinking of drilling a glass tank on the bottom...a lot of them are tempered nowdays and cannot be drilled. If the tank bottom is not marked or labelled then contact the manufacturer and find out what it is

G

[phidelt85]

Just a warning for anyone thinking of drilling a glass tank on the bottom...a lot of them are tempered nowdays and cannot be drilled. If the tank bottom is not marked or labelled then contact the manufacturer and find out what it is

G

Very good point, Graham. I know if you have an AGA tank, the specs page on their website will tell you whether the bottom is or not

[Jeff]

I drilled the bottoms of both acrylic and glass. No problems.

[tonymaccs]

There seems to be a perception that the bottom panel on the tank is the most highly stressed. While it is true that the water pressure is highest at the bottom of the water column, the base panel should be the least stressed panel in a full tank. This is because the base is supported and the sides are not.
If the base is fully supported then the downward forces of the water column are resisted by the base support and the resultant stresses (compressive only) in the base panel are not an issue.
The vertical panels are a different matter as they are only supported by each other around the perimeter. The water pressure induces bending forces accross the panels resulting in tensile stresses on the outer surfaces which are the limiting factor to the depth of water the tank can hold. The purpose of the stiffening bar at the top is to reduce bending stresses, but this does not eliminate them.
Adding holes to the equation provides a location for the stresses to concentrate, which will ultimately be where the crack will form at failure.
Of course there are factors of safety with properly designed tanks so that this doesn't often happen, but the tank bottom is the safest place to be drilling holes if you have a choice.
When drilling holes in the sides, keep in mind the tensile stresses are highest in the upper half of the panel, not in the lower half as might be expected.

[Blackwater Aquaria]

There seems to be a perception that the bottom panel on the tank is the most highly stressed. While it is true that the water pressure is highest at the bottom of the water column, the base panel should be the least stressed panel in a full tank. This is because the base is supported and the sides are not.
If the base is fully supported then the downward forces of the water column are resisted by the base support and the resultant stresses (compressive only) in the base panel are not an issue.
The vertical panels are a different matter as they are only supported by each other around the perimeter. The water pressure induces bending forces accross the panels resulting in tensile stresses on the outer surfaces which are the limiting factor to the depth of water the tank can hold. The purpose of the stiffening bar at the top is to reduce bending stresses, but this does not eliminate them.
Adding holes to the equation provides a location for the stresses to concentrate, which will ultimately be where the crack will form at failure.
Of course there are factors of safety with properly designed tanks so that this doesn't often happen, but the tank bottom is the safest place to be drilling holes if you have a choice.
When drilling holes in the sides, keep in mind the tensile stresses are highest in the upper half of the panel, not in the lower half as might be expected.

If my math skills are right for every foot of water in a tank = 2.34 psi if I am correct we are not dealing with much pressure atall.

[tonymaccs]

It's the way the pressure converts to bending stresses in the glass panels which is determined by the configuration of the tank. Like a lot of rigid materials, glass in much stronger in compression than it is in tension.

[scolley]

I got 8 bulkhead holes drilled in the bottom of my 180g acrylic. And I had 6 holes in the bottom of my 75g glass. No problems at all with the bulkheads. Ever.

Just buy quality bulkheads - NOT the cheap ones. And be aware of the fact that it complicates mounting the tank. The board it rests on obviously has to have holes drilled, and correctly aligned to the tank's holes. Same applies for the mat or foam if you have glass. It's a bit of a PITA.

And I find that it's easier to mount the bulkheads on the tank when it's not sitting on the stand. But that means that you'll need assistance in slowly lowering the tank onto the stand, aligning the bulkheads so they drop into the holes you've already drilled in the stand top.

[salth20]

I agree with Scolley. The bottom is the place to be. If you are placing the tank against a wall, you can get closer, and the whole thing is just sweeter if everything is under the stand.
My tank is in the wall, facing the exercise room. The tank is in a laundry room.. I still went with bottom holes, just so I can service the tank easier from the rear. I recently added a closed loop under the tank. My acrylic tank was on the stand, in the proper position. Using a holesaw of the correct diameter, I drilled the bottom until the pilot bit was through the acrylic, and wood support top of the stand. I removed the tank from the stand, finished out the tank holes, and mounted the bulkheads. Then I switched to a slightly larger hole saw, and drilled the top of the stand, using the pilot hole. Worked out fine. You need the holes in the stand to be slightly larger to accomodate the bulkhead flange. (Not an issue on glass tanks, unless they are frameless. Actually I haven't seen a frameless glass tank in years, but was impressed by the Dupla line of tanks "back in the day".)
FYI, drill the acrylic with light pressure, and remove the bit frequently. I did this and would up with clean holes, and a lot of acrylic shavings. You are going too fast and /or too much pressure if a ridge of melted plastic forms around the hole saw. The ridge is difficult to remove, and makes it harder to get the bulkhead to seal.
Save the acrylic shavings. They will dissolve in weld on 3, making a thicker filler material for reinforcing or filling the inevitable imperfect joints us DIY'ers have a tendency to create. Good luck.