Pressure Test - Value Meanings?

[fishrising]

Hi All,

I had my recently acquired A serial 16610 pressure tested yesterday (@ 10 bar), and it passed. My watchmaker was very busy and didn't have time to go over the details.

Can anyone on this board explain what the values mean in the pic below? Also, is only a 100m (10 bar) test normal for a local watchmaker? Are units designed to test beyon 10 bar cost prohibitive for most local guys? Or should these machines really test to 300m?

[robsteve]

Ben:

If it is anything like the unit my watchmaker uses, the measurements are the deflection of the crystal. I assume if there is a leak the crystal/case will get change/deform a bit by the vacuum, making the measurement change more than a specified amount. This is probably detailed in the operating instructions for the machine. I also assume there are different values for different crystals/case materials. In other words a plastic cased watch with a plastic crystal may deform much more than a steel Rolex with a sapphire crystal.

Robert

[fishrising]

My apologies all, I knew I asked this once before and I just found the threads:

http://www.rolexforums.com/showthread.php?t=88740

http://www.rolexforums.com/showthread.php?t=84082

[robsteve]

Just did a google on the machine. It looks like it determines if there is a leak by the rate of deformation, not the amount. In other words, a leaking watch will continue to deform over time.

Here is a quote from the sales literature for the machine.

The pressure causes a certain amount of deformation of the watch. This deformation remains constant in the case of a fully sealed watch provided that the pressure remains constant. In the case of a leaky watch the air seeping into the watchcase results in an internal pressure equalisation which relaxes the deformation.
A microprocessor-based measurement system monitors any change in the deformation and calculates the leakage rate. This indicates by what percentage the original deformation is reduced per minute. The leakage rate is always referred back to a pressure of 2 bar to ease the comparison of measurements taken under differing pressures. A numerical result such as this is an objective quantification of the lea- kiness.

http://www.witschi.com/e/produkte/?sub=6

[fishrising]

Originally Posted by robsteve

Just did a google on the machine. It looks like it determines if there is a leak by the rate of deformation, not the amount. In other words, a leaking watch will continue to deform over time.

Here is a quote from the sales literature for the machine.

The pressure causes a certain amount of deformation of the watch. This deformation remains constant in the case of a fully sealed watch provided that the pressure remains constant. In the case of a leaky watch the air seeping into the watchcase results in an internal pressure equalisation which relaxes the deformation.
A microprocessor-based measurement system monitors any change in the deformation and calculates the leakage rate. This indicates by what percentage the original deformation is reduced per minute. The leakage rate is always referred back to a pressure of 2 bar to ease the comparison of measurements taken under differing pressures. A numerical result such as this is an objective quantification of the lea- kiness.

http://www.witschi.com/e/produkte/?sub=6

You beat me to it! Thanks!

[mcubed]

Hey Fishrising, I get my watches serviced at that shop, and bought my Sub there as well.

[Andad]

IMO a vacuum test is just an initial test to check if the watch is worth pressure testing it has no real value in terms of a 30 Bar pressure test. The seals are engineered to resist pressure not vacuum and some seals will actually improve with pressure - consider the crystal and case seals for example. As the outside pressure increases the case back seal is pressed harder to the case. It would take far less suction on the outside of the case to remove air from the inside of the watch.
The 10 Bar test is just that - a test to 10 bar. That is 200 metres depth short of a full test.
The test 'pressure' of -0.7 Bar means the air on the inside of the watch is pushing on all the seals at an internal pressure of 0.7 Bar (about 10 psi). Compare that to the >435 psi the seals need to contain at 300 metres.