As a follow up to an earlier
thread on dive watches which do not require crown locking or screw down crown, I contacted Alessandro Bettarini of Ennebi and he so kindly replied. How often does one get a straight reply from the founder of a watch company?
His explanation as quoted below:
For a long time I worked in a Florentine Company whose client was the Minister of Defence and mainly the Italian Navy. It does not exist any more. Its brand now is famous among watch collectors.
We produced equipments and device for divers Corps. In some devices I used a special gasket to have water tightness on rotating shaft. I use this gasket on Fondale.
With this gasket more is the pressure more you have tightness. It is more expensive than normal oring and it needs enough space for a proper seat. Here you may see some documents.
The documents send by Alessandro:
Article describing the sealing technology on the Ennebi Fondale.
A 3D blowup of the Watch casing components
A 3D sectional view of the watch casing showing the location of the special spring energised seal. Label added by me.