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Water Tests Explained

by Jordan Ficklin

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Water resistant watches need to be tested or there can be no guarantee that they will perform as they are supposed to. When a watch maker performs a water test the price usually includes the necessary tasks to ensure the watch passes the test but not the parts needed to make it pass, should it fail. The watchmaker should clean the surfaces for the seals and lubricate the gaskets with a silicon grease. Simple o-ring gaskets will be replaced if necessary.

A water test (pressure test) should be performed every time a water resistant case is opened (like to change a power cell) or if there is any reason for concern. The silicon grease on the gaskets helps them to stay pliable longer, helps them to create a better seal, and keeps them from deforming when the case back is screwed on.

Water TesterThere are two main ways to test a watch’s water resistance: using a wet tester or a dry tester.

Wet Testers: Wet testers use water (obviously) and pressurized air to test a watches water resistance. They consist of a sealed container filled part way with water and a pump to change the air pressure within. They are used in a variety of ways. — One method increases the air pressure inside the container while the watch is still in the air and then lowers the watch down into the water. The excess air pressure is then released, if the watch’s seals leaked then the pressure inside the watch case increased with the air around it and when the pressure is released the pressurized air escapes from the watch case forming a stream of air bubbles coming out of the watch case into the water.

Another method submerges the watch in the water and then decreases the air pressure forming a vacuum. When the air pressure decreases the relative pressure in the watch is higher than the water around it and if the watch leaks air bubbles will escape. This is a stronger test than the first because the decrease in pressure pulls the case apart instead of compacting it.

A third method creates a real life situation. The watch is placed under the water and the pressure is increased to simulate the pressures experienced at the rated depth. If the watch fails water enters the watch. — Ouch!

With all three wet tests after the test is performed the watch is examined to see if any water entered the case. This is done by heating the watch (by placing it on a hot plate) and then placing an ice cold drop of water on the crystal. The heat vaporizes any moisture in the watch and this moisture condenses on the crystal when it is super-cooled. If the watch fogs up it failed.

Rolex uses the second and third methods to test their watches.

Dry Water TesterDry Testers use a different method all together. They don’t use any water so there is no risk of damaging the watch but if a watch fails you need to use a wet tester to locate the point where the watch failed. (This can be done with the movement removed from the case.) Dry testers support the watch case between two sensors. The watch is placed inside of a dome and the air pressure is changed. First the pressure is reduced and the sensors measure the deformation of the case (in thousandths of a millimeter). When exposed to the vacuum the case should expand and when exposed to increased pressure it should compress. If the case leaks the pressure equalizes and the case doesn’t deform at all. Omega, Breitling, Cartier & Most other brands use dry testers.

The downside to the dry tester is that watches need to be water resistant (not air pressure resistant) and some watches just can’t be tested by the dry tester. For example, if you place a professional series Rolex, like a Submariner, in a dry tester it will almost always fail. What? I thought the Submariner was the ultimate dive watch, why does it fail? Well, it doesn’t really fail but the machine thinks it does. That’s because the machine looks to see if the watch case deforms. The Submariner case is so sturdy that despite being exposed to high air pressure the case doesn’t deform enough for the machine to correctly register it. The machine (not knowing what kind of watch is inside of it) thinks the pressure must be equalizing when in reality the materials are just so strong they don’t deform inside the machine. — But, if you think the watch might fail, it is safer to use the dry tester.

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One Comment

  1. Prem
    Posted May 13, 2008 at 12:05 pm | Permalink

    JP- You have excelled in your quest of finding the right answers for water resistance and the different checking machinery available out in the marketplace. There are simple rules, and discipline is the key! Knowledge can only go as far as to teach you the basics, and your basics are spot on…!
    Cheers and a great day to yourself,

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