Reply With QuoteNo. The crystal already designed and selected will work fine. The time for suggestions was before it went to manufacture.
Eddie
Hi. I'm glad to be back to the forum after quite a while away (I've missed it). One thing I've always been curious about as regards Eddie's new Speedbird 3 design is why no apparent consideration has been given to utilizing the original "stepped" crystal design. If you want this watch to meet or exeed the original 1948 JLC/IWC MK XI specifications for resistance to negative pressure, the original "stepped" crystal is the only crystal design that can do that, and is at the same time compatible with an interchangeability between scratch-resistant saffire glass crystals and the tougher shatter-resistant acrylic crystals (i.e. creating the possibility of making us all happy as regards each our own preferences in crystals). However, the apparently current pre-production prototype design of the Speedbird 3 calls for a simple cost cutting press-fit crystal design that is very limited in the perimeters of it's ability to resist negative pressure, especially under extreme temperature changes, which, of course, is why the original MoD MK XI design required that the "stepped" crystal design be utilized for these all-out, uncompromised military pilot's watches that apexed 60 years ago. For my two cents, I'd rather pay extra for the slightly more complicated "stepped" crystal design for the otherwise near perfect Speedbird 3 as proposed. Maybe you could weigh in on this Eddie (and thank you if you do). Thanks again, Rollon :study: :idea:
No. The crystal already designed and selected will work fine. The time for suggestions was before it went to manufacture.
Eddie
Whole chunks of my life come under the heading "it seemed like a good idea at the time".
Thanks for your response Eddie(you were fast at it). I did not know the Speedbird 3 design was locked in yet and actual production was underway. Oh well, I would appreciate it, though, if you would consider the "stepped" crystal design for a possible future "Speedbird 4" (I'm patient--I think). Besides, for me, there's always the PRS-14. Thanks Eddie, take care, Rollon
Actually I believe the issue had been discussed. Modern glue-in crystals can easily be tested to a pressure differential of 1 bar, so I don't see how they would fail under normal circumstances.
However, I would appreciate if you could say a bit more about the influence of rapid temperature change on the crystal seating.
Cheers,
Martin ("Crusader")
Not knowing what the original 1948 spec called for, I cannot say if a press-in crystal, sapphire or mineral with gasket, will meet or exceed it. But, for practical purposes, sudden exposure to ambient pressure at 36,000 feet (11,000 meters) is about all the unprotected human body can withstand, so more would be silly for a watch, and a simple press-in crystal can easily neet that requirement.
Pressed in glass (sapphire or mineral) can take quite a bit of internal pressure before popping out. In excess of 1 atm, depending on the diameter of the crystal, is quite possible.
I am curious: will a large crystal pop out at a higher, or at a lower pressure differential than a crystal with a smaller diameter?Originally Posted by lysanderxiii
Cheers,
Martin ("Crusader")
Internal pressure in pound per square inch, the more square inches, the more pounds.
The average pressed in crystal can withstand about 10 to 15 pounds of force before unseating, with a pressure differential of 11 psi (approx 36,000 feet) a 28.5 mm diameter crystal will see about 11 pounds of force, and might stay inplace, a 34 mm crystal will see about 15.5 pounds of force, and may not.
Thanks, Lysander ... one learns something new every day. :-)
Cheers,
Martin ("Crusader")
Out of interest, how many people on here have ever had a crystal pop at high altitude? Just trying to get a feel for how widespread the problem is.
Eddie
Whole chunks of my life come under the heading "it seemed like a good idea at the time".
A friend reported someone else's watch crystal pop out during a tinnitus-treatment session in a low-pressure chamber. But that wasn't an aviation watch, presumably.
Oh, and out of interest, how many dive-watch ownhave taken their watch to the depth stated on their watches? :P
Cheers,
Martin ("Crusader")
Eddie...I have flown in unpressurised jets many times (I think the max was probably around FL240) and never had a crystal pop even on cheap watches. I don't think this is an issue at all.
Crusader...I am surprised he was allowed in the chamber with any jewellery/watches etc on him.
Chris.
The 6B/159 watches of the RAF were replaced by the Mark 11s not only because of the latters' antimagnetic protection (some terrain-following radar necessitated that), but also because the 6B/159 crystals were prone to popping during rapid depressurization of the then newly introduced pressurized cockpits.
Cheers,
Martin ("Crusader")
Personally, Im sick of it happening every time I go upstairs :twisted:
After having read a few reports from B-29 crews during WW2 and training in the late 40's and 50's (the B-29 and the later B-50 were prone to have the gunner's blisters blow out at altitude) a crystal in the watch is a minor problem.
In one reported incident, the upper blister in the gunner's compartment blew out, two of the gunners were strapped in, they lost their headsets, all the loose gear in the compartment, and even the seat cushions they were sitting on at the time of the blow-out, in addition to having a serious case of ear-ache. The third gunner, whose blister was the one that blew out, was fortunately, not in his seat but on the flight deck with the pilots, forward of the bombay, it was estimated that the air rushing through the tunnel between the two compartments reached 120 mph.
I wonder how the number of altitude popped crystals, compares to the number of helium blown seals.
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