O rly? When's the last time you saw glass flow at room temperature? For our discussion, given the limited time involved, a glass is a perfect description of a rigid vessel. If all you want is to find a mistake in my reasoning, you've picked a poor one.
Er, ah, well have you ever dropped a drinking glass on the floor and it bounced but didn't break? Ever pushed in the middle of a large window pane? Did it deflect? Was that because it's perfectly rigid? Please explain.
There is no such "spring" tension in any of your bladders.
Not true. Pure Urethane films have considerable elasticity. We've inflated *just the bladder* outside of a wing shell. At OPV pressures (~2.5 psi) they stretch quite a bit, but do not deform. Eventually they burst at high enough pressures. The wing shell limits the volume the bladder can achieve to well below the point where it stretches. Of course this entire discussion is a red herring that has zero bearing on the issue at hand.
I have to ask: have you done this? If not, why not? SS sheeting would make a poor bladder choice, so why bring it up?
One more time, you claim the "suppleness" of the bladder will impact how much water will enter a BC in normal use. Apparently you have some misconception that two flat pieces of material welded together can't return to zero volume. My example of stainless steel was used precisely because
.062" stainless is just a tiny bit stiffer than the stiffest materials used for bladders, yet one could inflate my example stainless bladder to low pressures, well below the yield point of the stainless, and it would return to zero volume when vented.
Fluids and gases *always* flow from areas of high pressure to lower pressure, the laws of physics demand it.
Ah yes the out of context quote, just what I expected.
I guess I have to detail this step by step.
1) What is the subject of this thread?
A: How does water enter a BC
2) What popular myth was offered several times?
A: Leaving the dump open after the wing was empty leads to water in the BC.
3) What would be required for such a phenomena to occur, i.e.
water to flow into a completely empty BC.
A: Pressure differential.
That's way I first said
Water doesn't get into a bc because the exhaust was held open too long, i.e. after the bladder was empty. There is no pressure differential to cause this.
Followed by
Fluids and gases *always* flow from areas of high pressure to lower pressure, the laws of physics demand it.
To explain that a pressure differential would be necessary for fluid movement into an empty BC.
Note the 2nd statement says
nothing about the relative pressures inside and outside a bladder. It discusses fluid flows only. Still not sure how you thinks this contradicts my specific, clear statement immediately preceding it.
BTW, gravity has nothing to do with it either. The gravity exerted on the air and the water are constant. The only issue is density as demonstrated by Archimedes Principle.
Next I expect you to tell me that mass and weight are the same thing.
If I have a bottle 1/2 filled with Oil and 1/2 filled with water on the surface of the earth (or anywhere else there is gravity) the less dense oil will "float" on top of the more dense water. Why?
Because of the
forces of gravity.
If I travel to zero gravity environment such as outer space can I expect the less dense oil to still float on the water? If not why?
Density is mass per unit volume, it's not a
force.
https://en.wikipedia.org/wiki/Density
Without the *Force* of gravity you wouldn't have buoyancy...........
https://en.m.wikipedia.org/wiki/Buoyancy
Now if we wish to do "work", i.e. displace a mass some distance, gas out of a BC or water down a power inflator and corrugated hose we are going to need a
force.
That's why I said
When these valves are opened this water runs down the corrugated hose as the gas flow out, the force at play is gravity.
Physics 101 kinda stuff.......
Tobin
---------- Post added October 18th, 2015 at 02:25 PM ----------
I'm sure you guys are right and water doesn't enter an empty BCD but somehow I get a lot more water in my BCD when I end a dive too light and try every which way to get the last of the air out. Must be osmosis or something. Or maybe diving with too much weight or a mask with a purge or my split fins. But I still get more water in trying to purge the last drop of air out.
It's largely a function of how many times you dump. A Square profile dive results in a bit of water. A busier profile, training dive with a bunch of ascents or repeated attempts to get the last cc of gas out results in more water.
Tobin