Gaskets

Specification

Technical parameters

Overview

Water resistance in a watch is almost entirely a gasket problem. A case back, a crystal and a crown tube are rigid parts that cannot seal by themselves; the sealing is done by elastomer rings compressed into a controlled gap. Every one of those rings has a working life.

Most watch gaskets are nitrile or silicone O-rings, sized by inside diameter and section thickness. Some are flat profile gaskets for case backs, and crown tubes use small O-rings inside the crown. Material matters: nitrile is a good general choice, silicone tolerates temperature better, and fluorocarbon resists chemicals and ozone at higher cost.

Gaskets age. They take a compression set — permanently flattened — and lose the ability to spring back, they harden, and they crack. A gasket that has been in a case for five years is not a gasket any more. Any time a case is opened for service, the seals should be replaced as a matter of course, because a seal that has been disturbed once will not reseat identically.

What matters about it

• Provide essentially all of a watch's water resistance
• Aged gaskets take a compression set and stop sealing
• Material chosen for temperature and chemical resistance
• Must be greased with a compatible product
• Replaced on every service, not only when visibly damaged

Practical notes

• Replace gaskets every time the case is opened, without exception.
• Check the gasket seat for scratches before fitting a new seal.
• Grease lightly with a product rated for that elastomer.
• Pressure-test after sealing — never assume.

Compatible with