Pressure Testing of Watches

Watch Pressure Testing .
Rubber or Silicon "O" rings keep the moisture out of your watch. But over time these deteriorate and require replacement.
Let's clear up some common misunderstandings. Your watch is not "pressurised" and isn't "repressurised" and the watchmaker didn't "break your water proof seal"!
When a watch is under water, the deeper you go, the greater the pressure and water is trying to force its way into the watch to equalise the pressure.
So the term "Pressure Test" comes from the fact the watch is put under pressure to test its Water resistance. So how does a Pressure Tester work? The main trick is the watch is tested with Air Pressure not Water Pressure. The watch is suspended in a clear chamber above water deep enough to submerge the watch in later in the test. The chamber is sealed and more air is forced into the chamber and thus the atmosphere inside the cylinder is now at an elevated pressure. If the seals are leaking some air will force its way inside the watch, so the watch is suspended here for a suitable timeframe to test the watch. The watch is now lowered below the surface of the water and the pressure slowly released. If the water has failed the pressure test, air bubbles will be seen escaping from the point at which the watch will leak. Important to note here Air is seen escaping NOT water entering, so even if the watch fails the test it is not damaged.
One final note, whilst a Pressure Test is for checking that Water Resistance is up to scratch it is also a test that ensures the watch is well sealed, and for a watch to give long term reliable service, it must be well sealed.