Seiko & Citizen Watch Forum Message Archive

The brilliance of Seiko's approach to the helium-entry problem lies in the way they thought outside the square. Instead of going the familiar venting valve way, they tackled the problem from first principles by eliminating (as far as possible) the entry of helium in the first place. To do this they used a one-piece case, and used a new gasket material which was virtually impervious to helium. Now, the equation for determining the amount of gas entering the case is given by:

Q = K(P1-P2)at/l (I think that's right), where

Q=quantity of gas entering the case

K=penetration coefficient of the gas (determined by the gasket material)

P1=outside pressure

P2=inside pressure

a=x-sectional area of gasket

t=time

l=length of water-sealing portion of gasket.

From the equation, it can be seen that the amount of gas entering is directly proportional to the penetration coefficient, the pressure differential, the cross-sectional area of the gasket and the amount of time spent in the gas environment. It's also _inversely_ proportional to the sealing length of the gasket, which is why the L-shape was developed. So you see, both the nature of the material of the gasket, and its special shape, were vital in achieving the aim of cutting down the amount of helium entering the watch to virtually zero. Simply brilliant!

GLSM IBC, Rep. Bellm.

_Time runs differently for watchmakers--a week to them is a month for everyone else._