Seiko & Citizen Watch Forum Message Archive

The secret inside the Seiko Professional diver watches such as the 600m automatic, 600m quartz, and 1000m quartz versions, is their "L packing" (rubber gaskets), according to Ikuo Tokunaga, Seiko Japan Watch Specialist.

Ikuo Tokunaga

When working on the problem of how to develop a professional Seiko divers watch which could be used for saturation diving (SAT), it was Tokunaga who came up with the unique idea of developing a rubber gasket which only small numbers of helium particles could penetrate.

The gaskets have two unique features -- both the rubber material used to make the seals, and the shape of the gaskets.

" 'L packing' started with the development of a new rubber material. During professional diving using a helium gas mixture, the inevitable problem is the invasion of helium gas and it's build up inside the professional divers watch. Simply explained, helium gas has a small atom which can easily get inside the watch. So, when a diver comes up from a dive as the pressure decreases it remains high inside the watch. This creates the danger that the watch's crystal will break. Other major manufacturers, such as Omega and Rolex, have dealt with this problem by using a "helium relief valve" to vent the gas inside the watch and the higher pressure inside.

"[It was] Mr. Tokunaga who got an unexpected idea, which other brands in the world didn't even imagine. He got the idea to seal the watch using rubber which would stop the invasion of the gas itself."

By switching from using seals made from "Nitoriru Butajen Rubber" (NBR) to "Isobuchirn Isopuren Rubber" (IIR), Seiko engineers were able to reduce helium gas invasion to 1/100th of the previous level.

Since helium gas not only invades a watch directly through the rubber material itself, but also through the microscopic space where the rubber meets the metal parts of the watch to make a seal, engineers also changed the shape of the gasket making it's cross section look like the letter "L". This prevents gases, as well as water at extreme depths like 1000 meters, from entering the watch by making the gasket seal better both vertically and horozonally.

"L" gasket material. Unfortunately, the outline of the shape of the gasket is not sharp in this scan because the contrast on my scanner is too dark. But, perhaps you can make out the shape of a letter "L" laying on it's side.

The chart below shows test results using a Seiko 600m Professional divers watch over the course of what appears to be 17 days.

Profiles "A", "B", and "C" show the buildup of helium gas in three other (un-named) makers' professional diver watches. The flat line on the bottom of the chart shows the results achieved with the Seiko professional watch with "L packing". As an aside, it was mentioned that several other makers' 200m diver watches went so far off the chart in tests the results were not listed here.

Test results.

To repeat, I guess the main points of this article were twofold. It is both the special composition of the rubber material used in these gaskets, as well as their unique shape, which allows Seiko to manufacture professional divers watches which can be used during SAT diving but not need a helium relief valve.

1975's 600m Automatic.

600m Automatic diagram.

1978's 600m Quartz.

600m Quartz diagram.

1986's 1000m Quartz.

1000m Quartz diagram.

Vintage 600m Automatic dial from 1976.

Vintage 600m Automatic case back.

Information from: "Watch BEAT; HYPER WATCH & SHOP MAGAZINE, Vol. 2" (Narumido Publishers, Tokyo, Dec. 2002) page 116 - 117. ISBNT1108658120565. It is from a new article entitled: "The Secret Story of World-leading Seiko Technology"