Chronograph pusher seal replacement and water resistance test.
Watch resistant watch cases can allow water ingress over time, often due to degrading seals such as the one at the case back. There is also a seal in the crown, and any other holes in the case where there are pushers, for example. Usually, these can be resolved by changing crown and pushers as complete items but, not all vintage watch collectors like to change original parts unnecessarily.
Crown seals are usually very difficult to extract and replace but it can be possible with pushers due to their construction. This study is for a 1971 Omega Speedmaster, calibre 861, aka the “Moon Watch”. After removing the movement from the case, the pushers were separated and the components are as shown below. The black smears in the upper area are what is left of the pusher seals so, they were certainly not sealing the case at all. The rings at the lower are washers used to hold the seals into the pusher outer bodies which are still attached to the case.
These parts are cleaned and appropriate new micro O rings selected such that the external diameter will fit in the case and the internal diameter is that required for the pusher.
The seals and closing washers (which should snap in) are fitted to the case.
The crown seal on this particular watch looks in good condition so a crown replacement is not needed. Here, the pushers are re-assembled and fitted with the crown, a new case back seal and the case back.
The wet tester is used which will show any areas that leak as a steady stream of bubbles. The test works in the following manner:
The tester chamber is half filled with water. The watch is placed in the air gap above the water and the pressure in the chamber increased to simulate a depth of 50m in water – that being 5 bar with a 25% safety factor giving 6.25 bar (approximately 92 p.s.i or 5 atmospheres) in total. This may be seen on the black scale of the gauge in the lower area of the image.
The watch is left to soak in that high pressure air for 30 minutes to an hour. If the case is not sealed, then the high pressure air will leak into the case and the inside of the case will achieve the same pressure as in the rest of the chamber, namely 6.25 bar. The watch is then inserted into the water.
The pressure in the chamber is then released in a controlled manner and, if the pressure in the watch is now at 6.25 bar because the case leaked, then it will try to escape due to the reducing pressure in the water. This will be seen as a steady stream of air bubbles. In the picture below with the chamber pressure reduced to 4 bar, there is no steady stream of bubbles but one bubble may be seen as some trapped air escapes from under the bezel – as the bezel is mounted on the outside of the case, this is not important.
Before the gauge pressure drops to zero, the watch is extracted from the water. This watch passes the 50m water resistance test and the existing pushers (with new seals) and crown can be retained.