Question What is that valve on that tank?

[LI-er]

weren't they known as suicide bottels or something like that?

They enjoyed a brief period of popularity during a time when a guy who was in the process of divorcing his wife would take her on a scuba diving excursion and tell her that by the end of the dive their ongoing problems would be solved.

 

[BRT]

Pretty sure that is a Spare Air tank with the refill adapter on it that lets you fill it off a normal scuba tank.

Nope

 

[Mobulai]

now how would such a valve be removed? to replace with a normal DIN valve for example?

EDIT: just realized they have a different thread on the neck.. futile