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August 1999

Timepieces:Education & Repair

Water Resistance Tests: Why and How

Once you understand how the tests are conducted, you can offer a valuable service by explaining them to customers

By David Christianson
Certified Master Watchmaker
President, American Watchmakers-Clockmakers Institute

Pressure is a bad thing in life but a good thing in a watch because it keeps water out of the case and away from the movement. In this second part of an article on water resistance (see also "The Need for Water Resistance Repair," p. 64, July 1999), we examine how rubber gaskets and the case work together to protect the delicate watch movement from dirt and moisture. If your store can conduct the test efficiently, customers will likely consult you again for future purchases and repairs.

Gasket, Case
One basic rule: the thinner the gasket, the less protection it will provide. For instance, the 0.4mm case back gasket provides minimal protection against accidental exposure to rain and moisture. A watch with this gasket most likely couldn't resist the pressure and would leak if placed in only one meter of water (about 3 feet) in a pool, lake, tub or spa. At this depth, the watch case is subjected to an additional 1.3 pounds of pressure (measured in pounds per square inch). Under 10 feet of water, the case would face an additional 4.3 pounds per square inch and would leak even faster.

As with the gasket, the thicker the case, the better the protection. While thin versions of both can be used for minimal resistance, the thicker cases and gaskets found on diver watches and others provide stronger resistance to pressure.

Pressure Testing
A watchmaker or watch repair person should look at gaskets routinely when checking water resistance. This is done typically after servicing a watch movement to assure it remains dry and dust free within the limits stated on the watch.

These tests are done in a workshop with a pressure tester (either wet or dry) or a vacuum test (used primarily by large-volume test centers or retailers).

The wet pressure tester is most common among independent jewelers. The watchmaker places the cased watch without its strap on the shelf in the upper dry half of the tester and sets the pressure control to the limits indicated for the watch.

Once the pressure is built up in the tester, the repair person lowers the watch into the water-filled bottom half. At this point, the air pressure in a leaky case would be equal to the pressure of the water in the tester – water couldn't enter and air couldn't escape. But when the air pressure valve on the tester is released, the air in the leaky case would have greater pressure than the water around it.

In the case of a leak, bubbles form, showing the faulty section of the gasket or the problem section of the case. If the watch is removed immediately while the air is still escaping, it isn't damaged.

If no bubbles appear, the case and gasket are holding out water at the indicated pressure. The seals are deemed tight and the gaskets are secure.


David Christianson is fourth-generation owner of Christianson Jewelry, Kendallville, IN. In addition to serving as AWI president, he is a certified master watchmaker and a fellow of the British Horological Society. He discusses watch repair for the sales staff in this column each month. Send questions, suggestions and comments toProfessional Jeweler, 1500 Walnut St., Suite 1200, Philadelphia, PA 19102; askus@professionaljeweler.com.

Copyright © 1999 by Bond Communications.


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