BDLJ
4653
Some maths
A simple question re: pushers. Why are non-screw chrono pushers not activated at depth? If there's enough "drag" to cause deflection of the stem then what about the static pressure inadvertantly depressing a pusher.
So, what is the force on the end of a pusher?
(now this is all done in my head, so I beg forgiveness if it is stupidly wrong)
Pressure=Force / Area.
50m=5 atm=5 kgf/cm^2 approx.
Area of pusher=(assume 4mm dia pusher) pi x r^2
using 3 for pi (I like simple numbers!) gives us: 3 x (0.2)^2=0.12
So back to P=F/A:
5=F/0.12
0.6=F
So at 50m there is roughly 0.6 kg (~6 N) on the end of the pusher. And 50m is pretty deep.
(Out of interest, what is the force on the dial? if we assume 40mm dial: 60kg (~600N).... dare you stand on the dial?
I will do some delving in my old fluids texts for dynamic pressure to work out the sideways force on a crown. but the above gives the magnitudes of forces involved.
Something to dwell on.
Please comment on any of the maths or assumptions, all feedback is great.
This message has been edited by BDLJ on 2008-12-04 16:19:07
can u trust the 5 atm water resistance?
a reverso in SS case stated 5atm with an articulated rubber bracelet is supposed to be water friendly. would u want to wash it under running tap? note there isn't any sophisticated protection to the crown. really appreciate your opinions! thx all experts!
Hi, Paullin,
Have in mind the the 5 AT are ok if you don't forget to check the etancheity joint each year, my friend, as for every watch. In this case, yes, I will be confident in thre water resistance of your Reverso. Don't forget that 5 AM don't mean that you can sw...
it is just purchased from an AD, so
i guess i can simply enjoy showering with it until i need a check in a year time! btw, nicolas, i love reading ur posts all the time even during at work!
Nicolas. I didnt really get the difference...
... about the swimming and showering. Whats 5 AM and 5 AT? Isn't 5 ATM, the equivalent of 50m water resistant? Tnx. Karim
But the JLC manual says 5atm is okay for swimming
Or is that only the case for 5atm Master Control watches, and not Grand Sport Reversos? That cannot be true--5atm is 5atm, and JLC says swimming is fine, but not diving or other water sports. DJK
The depht is one thing, the pressure is another one, my friend
When you swim, you have pressure wth your arm " breaking " the water... This pressure may go above 5 ATM. If you want to swim with a watch, it is traditionnaly recommended to get a 10 ATM Watch. Best. Nicolas
Respectfully, this is an old wives tale
It is impossible to move yours arms with the necessary velocity to increase the pressure in any meaningful way. This is why swimming is absolutely fine (and the JLC manual *says* that swimming is safe for watches with 5atm WR). I would not worry at all ab...
Have you tried it then?
Have you tried swimming with a watch rated at 5atm with no screw down crown or compressor key? You're a very brave man if you have. regards Bretta
Sure
My Master Hometime got wet regularly (5atm) and I didn't worry because JLC indicated in the manual that it was fine to swim with the watch . I had no problems. I also got my RGM (no screw down crown, rated to 5atm?) regularly wet giving my son a bath. The...
yes and no
Hi Daniel, If JLC says it's OK to swim with it, then so be it. For my part I won't swim with a watch without a screw down crown. You're point about the speed of motion necessary to meaningfully increase the water pressure on the gaskets is well taken, but...
agree and disagree
I have yet to see any sort of evidence that splashing one's arms vigorously will achieve the sort of pressure change necessary to compromise 5atm of protection--the math simply doesn't work out. However, it is always prudent to have WR checked once/year i...
your response reads almost as if you didn't read my post
Hi Daniel, Of course you're free to disagree, but your post didn't indicate that you had read or understood that I'm agreeing with you about the (negligible) pressure change resulting from the motion of one's arms, just pointing out that the force of the ...
Sorry if I misunderstood
I agree that arm movements associated with swimming would exert any troublesome pressure on the gaskets or the crown/pushers (is there a reason to think that the pressure one these parts would be greater or worse than the same pressure directly on the gas...
I think the dual uses of the term "pressure" are confusing the discussion
Hi Daniel, Pressure with regards to water resistance can be thought of as consisting of static pressure (related only to depth (and minimally temperature)) and dynamic pressure (the additional pressure caused by motion of the fluid or an object in the flu...
Thanks--very clear explanation
I think this may account for the JLC recommendation in the manual against diving and other water sports. In any case, I found it interesting, so thank you. Would you be similarly concerned about allowing a watch with 100m WR, a screw-down crown, and a chr...
Some maths
A simple question re: pushers. Why are non-screw chrono pushers not activated at depth? If there's enough "drag" to cause deflection of the stem then what about the static pressure inadvertantly depressing a pusher. So, what is the force on the end of a p...
Radial force on a crown
Lots of simplifications here, so bear with me. I have simplified numbers so I can do them in my head and on the calculator in my mobile, so exact values are incorrect, but magnitude should be OK (and please correct me if I am wrong - I can take the embarr...
I think you're off by an order of magnitude
Hi BDLJ, I don't have time to double check all the math, but it looks like you converted 35 mm to 0.35 cm instead of 3.5 cm, which could account for a significant difference in the outcome. You've ignored the drag coefficient also, but that would presumab...
I think it's correct.
7 x 5mm=35mm^2=0.35cm^2 It's the rest of the maths I'm not confident of!
A question for you, John
Hope I did not come across as a smart-alec with the maths. It's something I have heard and seen before, but never calculated myself. And we know stuff on the internet is not to be trusted ;-). A question for you as a watchmaker who has opened far far far ...
In fact I heard that Nicolas only takes cold showers!!
Hi, 5atm is supposed to mean it can stabnd a water pression at around 50 meters (deep). Some say it is 50 meters from the shore! I would not take any information of this kind for a total security. The watch is indeed waterproof when new and under standard...