Jaeger-LeCoultre

ei8htohms
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I think the dual uses of the term "pressure" are confusing the discussion

Hi Daniel,

Pressure with regards to water resistance can be thought of as consisting of static pressure (related only to depth (and minimally temperature)) and dynamic pressure (the additional pressure caused by motion of the fluid or an object in the fluid). Dynamic pressure in normal ranges of motion is basically neglible, being somewhere in the vicinity of 0.5 BAR at 10 M/s. We are in agreement that dynamic pressure is not likely to push the gasket in a watch beyond their functional limits in normal use.

To avoid further confusion, I'll call the thrid consideration I'm bringing to the discussion "drag related deflection". Any solid body travelling through a fluid will experience drag. The sudden experience of drag when crossing the air to water interface can be traumatic, as anyone who's ever performed a belly flop knows. This sudden drag imparts a force on the objects experiencing it and can cause them to move or deflect from their normal position.

When this happens to the crown or pushers of a watch, it can cause them to deflect to the side, compressing the gasket on one side while potentially compromising the seal on the other. This drag related deflection can cause the seal to leak at basically 0 meters depth if only for a moment (long enough to get water inside). In this instance, this drag is affecting only the crown and pushers directly because the gaskets don't have any interfaces with the water that are not "shielded" to some extent by the crown, tube pusher cap or pusher tube. It is for this reason that diving watches are tested with lateral force applied to the crown and pushers, not only in case they get bumped about by rocks and such.

I can't think of any modern diving watches that don't feature some kind of locking mechanism for the crown, and I don't know if the older dive watches you referred to might have predated the current ISOs. My opinion is that a securing mechanism of some sort is important to attain real world water resistance.

Anyway, sorry for belaboring this point so exhaustively. I am admittedly conservative when it comes to my watches and water resistance. I have a watch rated for 100 meters without a screw down crown and I won't wear it swimming. I've seen far to many watches that are rusted beyond practical repair to take water resistance for granted myself.

_john