Internal overflow is safer than an external one!

[Henry100]

Both types of overflow do the same job,getting water into the sump.One main difference between them is that an internal overflow puts less stress in the tank than an external one.This happens due to the fact that an internal overflow has water around it(and especially below it),which helps in keeping the overflow at its position without stressing the tank too much.Something which does not happen in the case of an external overflow.

[wooden_reefer]

I don't think the stress of an external overflow box on the tank is significant, except in very small tanks.

I think an external one is not space efficient. You have to place the tank more outside, or you put the external flow box on the side, which I hate to do.

[BeanAnimal]

Where in the world do you come up with this stuff Henry?

I am not aware of external overflows causing tank failure :D

"It is safer to pick your nose with your left hand becuse if somebody punches you for being disgusting, you may end up with broken fingers and of course most people are right handed so the odds are obvious."

Henry, have you ever heard of "deep thoughts by Jack Handy?"

[Henry100]

<a href=showthread.php?s=&postid=10937692#post10937692 target=_blank>Originally posted</a> by BeanAnimal
Where in the world do you come up with this stuff Henry?

I am not aware of external overflows causing tank failure :D

"It is safer to pick your nose with your left hand becuse if somebody punches you for being disgusting, you may end up with broken fingers and of course most people are right handed so the odds are obvious."

Henry, have you ever heard of "deep thoughts by Jack Handy?"

I don't know anything about Jack Handy!Please be patient and careful before rejecting an idea(and especially my ideas).An internal overflow has a force pointing upwards,from the water below it.This decreases the weight of the overflow(which includes water),which means it puts less stress to the tank.An external overflow has air below it,which means the weight of the overflow(which includes water) is as we know it,m*g.This weight is obviously bigger than in the case of an internal overflow.:)

[woz9683]

Damn, I'm left handed.

The forces being exerted on the tank wall by the overflow are minimal at best (so this is really a moot point), but that's not why the statement is flawed. The stress on the tank wall can be greater with either an internal or external overflow box depending on the water level inside the overflow box. Let's say I have a 10" deep overflow box, but because of the durso, etc. it only has 2" of water in the bottom of it when the dursos are working properly. If this box is external, the weight of water is the force "pulling" at the tank wall. If the box is internal, it's the displaced tank water, pushing on the overflow box, that transfers its energy to the back wall. In this particular example, the internal overflow box actually pushes against the back wall with more force than the external box pulling on it. Take the exact same box and design the dursos so it has an 8" water level under normal operating conditions and the results are reversed. Now, the weight of the water pulling on the tank wall from the external box is greater than the force applied by the displaced water from the internal box.

Obviously construction methods on either type of box effect this significantly, but I think this holds true for your basic overflow box placed in the middle of a wall, not connected to more than one wall. Or maybe I'm FOS :D

[woz9683]

EDIT: The internal overflow has forces on it pointing out and up.

[BeanAnimal]

Henry...

My comments were not in regard to your application of physics (right or wrong)... they were simply from the perspective that it makes utterly no difference in the real world.

I get this funny feeling you spend a lot of time pondering ways to post profound statements. My inclination would be to tell you "Don't think so hard". Jack Handy was an SNL character that made deeply profound statements that made sense, but then again made no sense at all.

As always your posts are fun and of course somewhat odd. My remarks were made from that perspective.

[woz9683]

Cough cough...post count...cough cough

[Henry100]

<a href=showthread.php?s=&postid=10937995#post10937995 target=_blank>Originally posted</a> by woz9683
If the box is internal, it's the displaced tank water, pushing on the overflow box, that transfers its energy to the back wall. :D

This point is partly right because the displaced tank water pushes upwards and horizontal(against the tank wall),which means we have one force pointing upwards(which is helpful as I described above) and one force pointing against the wall of the tank.Also the decreased weight puts a force to the tank wall,pointing downward.This is what I mentioned above.Furthermore,an external overflow puts a w*d to the tank wall,pointing clockwise(if it is on the back of the tank and we see the tank from it's right end),which tends to push the back wall of the tank backwards.In the case of an internal overflow we have a weaker w*d(due to the weaker w) and an opposite direction.That's what caused me to start this thread.

[shyland83]

HAHA. I always try to folow your posts Henry. You are a master of making statements that you know people will disagree with just to get a response. keep it up man, gotta keep people on their toes.

[rustybucket145]

whooaaa... duuudddeeee... is my tank holding the water up... or is the water holding my tank down....

gnarley...

[BeanAnimal]

Henry you can be the first person to design the Cantilever Overflow or Cable Suspension Overflow to help combat the horizontal force vectors (torque) on the tank wall and transform them back into vertical force vectors (compression). Just remember to send part of the profits my way so that I can buy that bridge I have had my eye on :)

[Henry100]

Let's come to the conclusion.What I say is that between two overflows,one internal and one external,which have the same dimensions,the internal overflow puts less stress to the tank than the external one.

[shyland83]

"Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis."

[BeanAnimal]

Henry... the POINT is that it does not matter in the slightest.

Let's come to a conclusion. Given two rocks of the same size in the same tank, the rock that is deeper will have more pressure acting on it.

Nobody is saying that you are wrong my friend. We (me?) are saying that the point is more than a little moot.

[Henry100]

Yes,I don't know how much this subject could affect a tank,in reality,but for my own overflow I would prefer an internal one.Even if the impact of this choice is nearly 0.Just the thought that an external overflow has only air below it,keeps me away from this type of overflow.

[shyland83]

if it's assembled properly i don't think i would lose any sleep over it. i opted against external because i didn't have the space behind the tank, but otherwise i definitly wouldve went external.

[randallcentral]

You make a persuasive argument henry100.

[Acrylics]

Don't forget that an external box places an horizontal beam to the back of the tank, kinda like a eurobrace at the midpoint of the tank, providing a good amount of rigidity and usually offsetting any stresses put on the tank simply due to the added rigidity whether it's full of water or not. In most cases, internal overflows are made from thinner material than the tank structure with less gluing material at the top (teeth or not), so the internal overflow often requires water to be in it just to keep it from being stressed too much, esp larger ones.

While I'd agree that an internal will usually flow more than an external (3 planes working vs 1), to say one is inherently "safer" isn't exactly true, in acrylic anyway. I demonstrate the strength of tanks by picking up the entire tank from the external box, eurobrace, whatever, or standing on same. I have absolutely no fear of them failing, I wouldn't build them if I did.

James

[BeanAnimal]

<a href=showthread.php?s=&postid=10938429#post10938429 target=_blank>Originally posted</a> by Henry100
Just the thought that an external overflow has only air below it,keeps me away from this type of overflow.

I take it that you stay away from decks, balconys, bridges and other structures that have air under them? Is you aquarium stand a cubic solid and does it sit on a slab floor?

Henry I think this is one of those times where the facts just don't support the conclusions :)

You are big on spelling out the benefits of one design over another. I would have thought you would have made the "External overflows are better because they don't take up valuable tank realestate and allow for easier plumbing with fewer fittings." Or something of that nature.

You have a much greater chance of a tanks vertical seam failing than you do of your overflow being pulled away by gravity.

If you are set on an internal overflow, may I suggest a "Coast to coast" style (aka a Calfo overflow). They maximize surface skimming and are easy to implement.

[todd rose]

Wow!! Entertaining disscusion. Crank it up!!

[BeanAnimal]

Henry always creates fun threads :)

[kgolem]

<a href=showthread.php?s=&postid=10938183#post10938183 target=_blank>Originally posted</a> by Henry100
This point is partly right because the displaced tank water pushes upwards and horizontal(against the tank wall),which means we have one force pointing upwards(which is helpful as I described above) and one force pointing against the wall of the tank.Also the decreased weight puts a force to the tank wall,pointing downward.This is what I mentioned above.Furthermore,an external overflow puts a w*d to the tank wall,pointing clockwise(if it is on the back of the tank and we see the tank from it's right end),which tends to push the back wall of the tank backwards.In the case of an internal overflow we have a weaker w*d(due to the weaker w) and an opposite direction.That's what caused me to start this thread.

I'm sorry but I don't buy this at all. Unless the overflow increases the overall depth of the tank, displaced water cannot exert any more pressure than water that is not displaced.

Imagine; a tank of water, some water is removed and then replaced with new water till the tank is back to it's original depth. The stresses on the tank don't change from the original condition. Even though the original water is displaced by the replacement water.

An external overflow doesn't/shouldn't change the overall tank depth. So the pressures can't change.

An external overflow will apply torque to the tank wall and stress the corner seams and the tank side, as has been stated here.

An internal overflow will only add extra stress to the tank, from the stress caused by a no-overflow condition by the difference in mass of the overflow, and the mass of the water it displaces. This difference would be negative, unless the overflow is completely full, in which case it is not functioning properly. But the torque vectors between an external and internal overflow are in completely different magnitude and direction, not just direction of rotation.

Please allow me a pre-emptive apology if I am missing a crucial part of the discussion. But IMO, the differences in stress caused by one device over another, preclude any credible argument or discussion over which one is better. In either case, the effects are negligible, when the design criteria of the tank structure are taken into account.

[BeanAnimal]

Please allow me a pre-emptive apology if I am missing a crucial part of the discussion. But IMO, the differences in stress caused by one device over another, preclude any credible argument or discussion over which one is better. In either case, the effects are negligible, when the design criteria of the tank structure are taken into account.

Umm

Yup, that is pretty much what to walk away with.

[flyyyguy]

I wouldn't be surprised if someday some fishermen caught a big shark and cut it open, and there inside was a whole person. Then they cut the person open, and in him is a little baby shark. And in the baby shark there isn't a person, because it would be too small. But there's a little doll or something, like a Johnny Combat little toy guy---something like that.

[mfp1016]

Henry how can an internal overlfow box and an external overflow have the exact same dimensions? Also, are you taking into account the pressure of the water on the internal overflow box, ala rho*g*delta z?

Regardless, this is a terribly moot point, perhaps you should engineer your time towards more useful goals.

[hahnmeister]

I dont think internal or external makes a difference so much as how they are implimented in each design. I can see how either could either reinforce or weaken a tank depending on how they are done. Hole placement, placement of the overflow (height, corner or center, thickness of glass/acrylic, hole in the bottom or back, center of the bottom or along the wall, etc.). Just the material selection alone can change things... a welded acrylic tank is a different story from a glass/silicone one in some respects. Its trivial in the end. Either one can be made to strengthen or weaken. Also, with most overflows, I dont know about you, but I dont have the waterline much more than a few inches below the main tank's so that noise is kept down... so pressure differences are nothing much to consider.

[Henry100]

Thanks,kgolem!That was what I was trying to say.The torque applied to tank's back wall by an external overflow,relative to the axis which is the bottom back edge of the tank(as bottom edges of a tank have the biggest stress),has the same direction as the torque of the aquarium's water(relative to the same axis).This means we have torque1(aquarium's water)+torque2(external overflow).In the case of an internal overflow we have torque1-torque3(internal overflow).So,an external overflow puts more stress to the tank than an internal one.On the other hand,I think that the effect is limited because torque1 is much greater than torque2 or torque3,due to the greater w and d of the aquarium's water.It is torque1>>torque2>torque3.

[kgolem]

<a href=showthread.php?s=&postid=10941281#post10941281 target=_blank>Originally posted</a> by Henry100
Thanks,kgolem!That was what I was trying to say.The torque applied to tank's back wall by an external overflow,relative to the axis which is the bottom back edge of the tank(as bottom edges of a tank have the biggest stress),has the same direction as the torque of the aquarium's water(relative to the same axis).This means we have torque1(aquarium's water)+torque2(external overflow).In the case of an internal overflow we have torque1-torque3(internal overflow).So,an external overflow puts more stress to the tank than an internal one.On the other hand,I think that the effect is limited because torque1 is much greater than torque2 or torque3,due to the greater w and d of the aquarium's water.It is torque1>>torque2>torque3.

Pretty much all in agreement here, but the amount of stress is statistically insignificant when you take into account the absolute value of the torsional pressure imparted by the worst case external overflow compared to the pressures in various vectors that the tank is designed to withstand.

Like crashing your car into the base of Hoover Dam. It is going to make a helluva bang from the bystanders point of view, but resultant damage to the Dam structure will be cosmetic and of no significance.

One type of overflow is more stressful, worse if you will, but it is a stress level that is not worth taking into account, when considering a practical application.

[BeanAnimal]

Henry we can talk about the force vectors that your ears place on your scalp skin or the force vectors that the overhanging bacon place on your hamburger meat and cheese. We can do so in a very scientific way and draw conclusions like "Bacon extending unsupported from a bacon cheeseburger will place more force on the soft cheese and cause it to deform slightly more than shorter strips of bacon." The questions is not if the science is correct, but is it really worth talking about?

[kgolem]

<a href=showthread.php?s=&postid=10941613#post10941613 target=_blank>Originally posted</a> by BeanAnimal
Henry we can talk about the force vectors that your ears place on your scalp skin

So spectacles would be not as safe as contact lenses. :rollface:

[Fiziksgeek]

How did I miss this one...

Henry, as a physicist I find that there are an almost infinite number of phenomena that are more interesting that the torque applied by overflows. In fact, aquarium construction is pretty simple and very well understood, and does not warrant the brain power you are attempting to apply. In this case, and others, I believe your gross generalizations are not contributing to the greater good of the hobby, and at times are down right incorrect. Perhaps you have better chance of making a significant contribution over in the reef chemistry forum. I believe there are more discoveries to be made there! Who knows...in a year we might all be dosing Henry's Two Part...But not likely that we will be building tanks using Henry's Low Torque Overflows..

[shyland83]

Bean I think your making light of a serious subject. Unsupported bacon is a serious issue that deserves our time and research.

[BeanAnimal]

Who said I did not support bacon? I am on the "other white meat" council and am a staunch bacon advocate!

HOMER agrees with me!

Homer: Are you saying you're never going to eat any animal again? What about bacon?
Lisa: No.
Homer: Ham?
Lisa: No!
Homer: Pork chops?
Lisa: Dad, those all come from the same animal!
Homer: Heh heh heh. Ooh, yeah, right, Lisa. A wonderful, magical animal.

[mfp1016]

Are you an engineering student henry?

[RuhiA]

Wow...

[Henry100]

<a href=showthread.php?s=&postid=10945874#post10945874 target=_blank>Originally posted</a> by mfp1016
Are you an engineering student henry?

Yes,of course!:)