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.