Difference between air and water pressure

[vjb.knife]

Sorry for the wise-ass comment earlier. I suppose there are many people that do not have technical training that would make all of this very simple and obvious. Pressure is pressure whether it is in water or in air. A water column or depth in water produces pressure at a constant rate depending on the density of the water which varies from fresh water to salt (and can be a bit different due to the level of salinity). Since water is basically non-compressible the rate of change in pressure as you descend in water is constant, as stated earlier, about .445 psi (pounds per square inch) per foot of seawater. In the Atmosphere at sea level the absolute pressure standard at 67 degrees F is approximately 14.7 psia (pounds per square inch absolute) or zero pisg (pounds per square inch gauge). One atmosphere of pressure is equal to this pressure absolute at standard temperature at sea level is 101.325 kPa or in other units that are equivalent: 760 mmHg (torr), 29.92 inHg, 14.696 PSI, 1013.25 millibars.

The difference to a watch between air pressure and water pressure is none. The seals will operate the same and the watch will perform and or fail the same whether it is under 1000 psi of water pressure (about 2247 feet under seawater) or if it is in a pressure vessel pumped up to 1000 psi of air pressure.

The whole question about opening the watch case at high elevation is nearly nil since the amount of pressure change would be less than 1 atmosphere or 15 psi, which is miniscule to the pressure that a diving watch is rated. Change in elevation vs. change in absolute pressure is not a constant because air as a fluid medium is highly compressible, so the change in elevation can not be stated as a specific psia change per a certain change in feet in elevation and also because the relative density of air in the atmosphere is affected greatly by temperature, humidity, wind, etc.

The one problem you might have if a watch was opened at a very high elevation is that there would be a greater pressure exerted on it once it is brought back to sea level that could make it hard to open there. But with a screw on case back , the relatively large hand wench used to remove it and the relative low differential pressure between the interior of the case acting on the approximately 1 square inch surface area of the case back, it would pose no problem.

I apologize again for the initial comments. My response should have been - I feel that the issue that you have raised would have extremely little or zero effect on the watch.

[Lisa]

Thank you, Vince. There are people like me whose minds work in very simple ways. I appreciate those of you who want to take the time to explain some of this. As for me, I'm still wondering about the lume thing.

[vjb.knife]

Originally Posted by Lisa

Thank you, Vince. There are people like me whose minds work in very simple ways. I appreciate those of you who want to take the time to explain some of this. As for me, I'm still wondering about the lume thing. Erm... can't we just talk about how do it know when to turn the lume on?

Sorry, that one is over my head.

[Art161]

Thanks for the further explanation, Vince.

[Andad]

Originally Posted by vjb.knife

Please tell me that this question is also just being made as a humorous statement.

Which weighs most.

An atom of feathers or an atom of chicken.

[vjb.knife]

Originally Posted by directioneng

Which weighs most.

An atom of feathers or an atom of chicken.

Neither the real answer is tuesday.

[Art161]

Originally Posted by directioneng

Which weighs most.

An atom of feathers or an atom of chicken.

Originally Posted by vjb.knife

Neither the real answer is tuesday.

I thought Monday weighed most heavily on the majority of the people who expressed a preference. Better say to be safe.

[RsqVet]

also since you asked about the helium release valve --- it's need is due to the fact that saturation divers spend long times in compression chambers or divng bells pressurized with with a mixture of helium gas.

Helium being a very small molecule can pass around the O-rings, even on a rolex. This happens slowly.

Then the diver surfaces --- either wet or in the chamber much faster then the helium entered the watch and the pressure thus created INSIDE the watch can blow the crystal off it.

The one way valve eliminates this issue.

I have offten thought of pressurizing my SD in a helium filled chamber for a day or 2 just to see the valve open.... but to date have had better things to do.

[Z-Sub]

Simple answer,

Water is much heavier than air.

[Art161]

Originally Posted by Z-Sub

Simple answer,

Water is much heavier than air.

So a pound of water is much heavier than a pound of air?

(If Vince is still following this thread he is going )

[Z-Sub]

Originally Posted by Art161

So a pound of water is much heavier than a pound of air?

(If Vince is still following this thread he is going )

Care to dispute that?
You dive 10feet in water that pressure should be felt on your ear drum. Maybe not yours.
you go up one flight, you think you'll feel the difference in pressure.
Yes I made it so simple and you can pick whatever you like.
trying to be a smart a..?

[Art161]

IMHO, the serious part of the thread was finished at post #34, with the exception of post #38.

[vjb.knife]

Originally Posted by RsqVet

also since you asked about the helium release valve --- it's need is due to the fact that saturation divers spend long times in compression chambers or divng bells pressurized with with a mixture of helium gas.

Helium being a very small molecule can pass around the O-rings, even on a rolex. This happens slowly.

Then the diver surfaces --- either wet or in the chamber much faster then the helium entered the watch and the pressure thus created INSIDE the watch can blow the crystal off it.

The one way valve eliminates this issue.

I have offten thought of pressurizing my SD in a helium filled chamber for a day or 2 just to see the valve open.... but to date have had better things to do.

Divers do not ever surface in the water from Saturation Diving. This is done on the surface in the decompression section of the hyperbaric saturation system.

Don't waste you time trying to pressurize your watch with helium because even if you did you would never be able to see the HRV open when it decompressed the watch.

[wuzzzer]

Originally Posted by BigHat

Actually, there is no "legally" about it. Many posts about it. Do a search.

Also I have never heard your assertion regarding positive and negative pressure. The testing process as well documented as pulling a vacuum and assessing crystal deflection. Please tell us more about what you mean.

Edit: I pulled up one of the threads for you:
http://www.rolexforums.com/showthrea...ght=Waterproof

Well, I don't have a scanner but here's the printed information I have directly from Rolex:

In a document titled "The Difference is Clear - Six Degrees of Rolex Separation Expanded"
"Pressure-proof (Waterproof)
Others: Can only claim water resistance. Cases are spot checked or batch tested for water leaking into the case.
Rolex: EVERY Rolex Oyster case is placed in a water environment. It is then positively and negatively pressure checked."

Also, in a booklet called "Talking Points" printed by Rolex:

"WATERPROOF TESTING

One of the factors that has contributed most to the international success of Rolex Oyster is its waterproof case. It is therefore vital to make sure that each watch offers a guaranteed level of protection.
To this effect, each watch is checked individually in actual conditions of use.
The watch is submerged in a tank of water in which the pressure is raised to a value exceeding the guaranteed water resistance depth. Rolex Oysters are guaranteed waterproof at depths of at least 100 meters/330 feet. The Submariner and Sea-Dweller models are guaranteed at depths of 300 meters/1,000 feet and 1,220 meters/4,000 feet respectively, thereby giving ever greater security to the diver."

[Andad]

Originally Posted by wuzzzer

Well, I don't have a scanner but here's the printed information I have directly from Rolex:

In a document titled "The Difference is Clear - Six Degrees of Rolex Separation Expanded"
"Pressure-proof (Waterproof)
Others: Can only claim water resistance. Cases are spot checked or batch tested for water leaking into the case.
Rolex: EVERY Rolex Oyster case is placed in a water environment. It is then positively and negatively pressure checked."

Also, in a booklet called "Talking Points" printed by Rolex:

"WATERPROOF TESTING

One of the factors that has contributed most to the international success of Rolex Oyster is its waterproof case. It is therefore vital to make sure that each watch offers a guaranteed level of protection.
To this effect, each watch is checked individually in actual conditions of use.
The watch is submerged in a tank of water in which the pressure is raised to a value exceeding the guaranteed water resistance depth. Rolex Oysters are guaranteed waterproof at depths of at least 100 meters/330 feet. The Submariner and Sea-Dweller models are guaranteed at depths of 300 meters/1,000 feet and 1,220 meters/4,000 feet respectively, thereby giving ever greater security to the diver."

This might sound dumb but if Rolex pressurises every diving watch to "a value exceeding the guaranteed water resistance depth" do they then take the back of to check if it has leaked - even a little bit? Then do they test it again and again ?
I can understand the method by where they pressurise the watch in air and then submerge it in water to check for air egress when the pressure is released but can't see how you could pressurise it under water and be sure it hadn't leaked without taking the back off?

As for deflection under a vacuum. What has vacuum testing got to do with pressure testing?

Can it be that:- "It held a vacuum therefore it must be resistant to 30 Bar, 120 or 390 Bar of water pressure"?

[WaltherPPK]

Originally Posted by Art161

...

Also, my guess is that the watch probably is not air tight and that the pressure inside the watch equalizes to the ambient air pressure. I would think that an atom of water is bigger than an atom of helium.

Thanks!

No WAY! Water is an ATOM? Air is HELIUM? Things just got interesting!