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View of the helmet visor sealing system valve.

The valve on this helmet differs from the flight configuration. Other helmets on display (e.g., Slayton's and Grissom's) have flight-type helmet visor sealing system valves.

The helmet visor sealing system consisted of a visor, a pneumatic visor seal, and an on-off visor valve. Closing the visor actuated the valve and caused automatic inflation of the visor seal. The visor seal remained inflated until the deflation button on the valve (presumably the red button on the other helmets' valves but missing from this particular valve) was manually actuated by the astronaut.

Note the provision for the attachment of the visor-seal gas supply bottle hose at the tip of the valve.