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.
Internal overflow is safer than an external one!
- Thread starter Henry100
- Start date
wooden_reefer
New member
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.
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
Premium Member
Where in the world do you come up with this stuff Henry?
I am not aware of external overflows causing tank failure
"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 am not aware of external overflows causing tank failure
"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?"
<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
"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
Premium Member
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
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
BeanAnimal
Premium Member
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.
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.
<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.
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.
rustybucket145
New member
whooaaa... duuudddeeee... is my tank holding the water up... or is the water holding my tank down....
gnarley...
gnarley...
BeanAnimal
Premium Member
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
BeanAnimal
Premium Member
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.
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.
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.
randallcentral
New member
You make a persuasive argument henry100.
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
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
Premium Member
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.
