Questions regarding diver pieces

[steinmann]

1. Why are they equipped with a rotating bezel?
2. Sometimes I can see a 2^nd knob on the other side (at about 10 o'clock) on some auto divers; why is it there for? I don't mean the date or is it the day pusher as on Orient.
Thank you.

[Citizen V]

1. Can be used to time things, like diving.

2. Helium escape valves are usually located there.

[Dan Pierce]

1- To help calculate the amount of air left in the tank or how long a diver has been at a certain depth while decompressing.
2- Could be a crown to lock [and/ or adjust] an internal or external bezel.
dP

[steinmann]

2. Helium escape valves are usually located there.

Thanks. Can you pls explain? What is helium doing inside a diver watch? And why must it be exhausted?

[Citizen V]

This is how I understand it, and probably simplified. Since helium is the smallest atom, it can enter the watch around the o-rings and gaskets. It's useful for divers who are in dry helium atmospheres like diving bells. The decompression time on the way back up isn't long enough to let all the helium escape, so a pressure difference can build up. If the helium is not released, it can cause damage like popping the crystal off. The helium escape valve (manual or automatic) is one way to combat this. Another way is by making the case impenetrable to helium, like Seiko's 600M Spring Drive Marine Master. Believe it's rated 600M helium safe because of its gaskets.

[steinmann]

Thanks for your time.
You bring me back to a question I once asked here and could not get an answer: I come from the automotive field. I know that manufacturing a gasket that can withstand oil, grease, petroleum, extreme high pressures and temperatures is a fact. They are produced daily and are cheap and common. It is not rocket science any more. So why do we have to buy expensive (and dear) watches, and be bothered with replacing gaskets/o-rings every few years? Why not make the gaskets from materials that will be able to hold 10 – 20 years and even more?
I will be glad to hear your opinion.

[G-Junkie]

they probably are the same materials. They don't last as long probably because they're so much smaller (less material). Think snowflake vs ice cube. they're both frozen water, but the snowflake will certainly be the first to be liquidized once the ambient temperature reaches 1 degree above freezing point

[FunkySteve]

they probably are the same materials. They don't last as long probably because they're so much smaller (less material). Think snowflake vs ice cube. they're both frozen water, but the snowflake will certainly be the first to be liquidized once the ambient temperature reaches 1 degree above freezing point

To add to this, and maybe help further develop this idea, the amount an automotive gasket (or o-ring, bushing, whatever), wears over a given period of time (10 years for example), is proportionally a very very small amount of material.

That same amount of material worn from a tiny gasket in a divers watch is an extremely big deal.

You bring up a good point OP--automotive gaskets last much longer despite facing ridiculously harsh conditions. Watches, however, are more limited because a miniscule amount of wear is more detrimental to the design.