스피드마스터 문워치의 방수 3기압이어야 하는 이유 Speedmaster

speedmaster x-33 2nd 오너입니다. 관련정보를 알아보는 과정에서 일리있는 글을 발견하여 옮겨봅니다.

(출처: http://www.chronocentric.com/omega/technical.shtml#shock)

Why aren't the Speedmaster Moonwatch and X-33 Mars watch more water resistant than 30 meters?

The Speedmaster Moonwatch and X-33 are only water resistant to about 30 meters. This leads many owners to ask why OMEGA chose to not give them greater water resistance. But additional water resistance is not always an advantage.

Highly water resistant watches are designed to handle environments where the air or water pressure outside the watch is greater than the pressure inside the watch. A diving watch like the Seamaster Professional series that is rated to 330 meters can handle an external pressure of up to 30 times the watch's internal air pressure. The Speedmaster Moonwatch and X-33 are rated for 30 meters, or only about 3 times their internal pressure.

But pressure works both ways. Yet none of the normal water-resistance features allow a watch to handle excessive internal air pressure, which can occur using most any form of pressurized environment--a deep diving chamber, a spacecraft or even in a commercial jetliner.

• In a deep diving chamber using a helium rich air mixture, helium--the smallest molecule--seeps past the seals, allowing the watch's internal pressure to gradually equalize to the chamber's pressure. During decompression of the chamber, the helium cannot seep out fast enough, causing the pressure in the watch to exceed that outside of it.
• A watch on the outside of the astronaut's spacesuit will be exposed to little or no air pressure when he steps out for a spacewalk or on the surface of the moon.
• In a commercial jetliner, you are in a pressurized cabin because the air pressure at high altitudes is very low. On rare occasions, the cabin pressure may drop suddenly, causing the pressure inside the watch to be greater than outside of it.

The end result is that due to any these several reasons, the air pressure inside the watch becomes greater than the air pressure outside the watch. The tigher seals of a highly water resistant watch can prevent these pressures from equalizing as quickly as they might change in the environment. The weakest seal for handling internal pressure is that holding the watch's crystal. When internal pressure exceeds that seal's limits, the pressure will escape by causing the crystal to pop out.

This is why the Speedmaster Moonwatch and X-33 are not made waterproof to great depths. These air pressure difference issues occur in routine space mission events, rendering a watch that cannot handle them a danger to the mission.