Diving helmet, "spit cock" what is this piece?

[Rod_Espinosa]

First of all, Hello to all divers here.
I have never dive with a old diving helmet like Mark V or something, but we all know this helmet represent divers in general.

But today watching some pictures, I realise there is something that I don't know what it's.
US navy named "spit cock" is a valve.
Does any one know for what is this valve?

Thanks

 

[tbone1004]

deleted

 

[iain/hsm]

It's exactly what it says, in clear water you open it, suck in a mouthful of salt water and spit it over the window to
clear the inside of the glass from steaming up. In black water there is no requirement to use it.
I was trained in my diving days on the Royal Navy Siebe 12 bolt rig, Cant say for the Yanks Mk 5 but I doubt they would use it for suit venting pressure release either. For one thing the hole is tiny about 3/16 diameter, you would be there all day venting the thing.

Inside the helmet there is a small brass spout a bit like the modern plastic sports drink flip tops spouts. You also had to be careful with your teeth it was hard as heck to suck on.

 

[tbone1004]

It's exactly what it says, in clear water you open it, suck in a mouthful of salt water and spit it over the window to
clear the inside of the glass from steaming up. In black water there is no requirement to use it.
I was trained in my diving days on the Royal Navy Siebe 12 bolt rig, Cant say for the Yanks Mk 5 but I doubt they would use it for suit venting pressure release either. For one thing the hole is tiny about 3/16 diameter, you would be there all day venting the thing.

Inside the helmet there is a small brass spout a bit like the modern plastic sports drink flip tops spouts. You also had to be careful with your teeth it was hard as heck to suck on.

USN manual has it as an aux over pressure valve as well as the "spit" valve and some were apparently modified as an off board inlet

 

[Akimbo]

Spit-cocks are for sucking water into your mouth and spitting it on fogged ports... usually side ports since most hats direct air flow across the front and sometimes the the upper port also. Divers in freshwater have also been known to drink from them. A lot of hats don't have them. This thread talks a lot about heavy gear: A Brief History of Diving (before 1943)

This is the spit-cock on a US Navy Mark V Hat​

The exhaust valve serves as a relief valve to maintain the desired suit inflation. It functions very much like the adjustable back-pressure exhaust valves on modern drysuits. But unlike a drysuit valve, it has a chin button. You can bump it to dump air out for more negative buoyancy or pull it in with your mouth (seriously), which is really handy for lifting heavy stuff. I have wrapped my arms under a 200 Lb pipe, inflated the suit, and jumped across the bottom. You have to be really careful not to accidentally let go or you will head for the surface like a Trident Missile. We were told in school that the the exhaust valve was too small to handle the volume on such a rapid ascent so the suit would explode (unless you were very shallow) and you would fall back into the mud.

This is the exhaust valve on the same hat​

 

[Akimbo]

USN manual has it as an aux over pressure valve as well as the "spit" valve and some were apparently modified as an off board inlet

There is no relief function in the spit-cock valve. The hole is really small... like about 1/4" as I recall.