Desco 61000, Manual

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DESCO AIR HAT DIVING HELMET
Section 1. Instructions for use of the Air Hat.
How the neck seal works:
To achieve a watertight seal at the neck, the Air Hat makes use of a brass neck ring insert, a large O-ring, rubber
shims (if necessary), and either a neoprene/foam neck dam, or the stretchable neck yoke of a dry suit. When
these components are properly assembled and the insert is pressed and locked into the neck ring of the Air Hat,
two separate sealing points are provided against entry of water. The seals are interdependent and both must be
properly installed to provide maximum watertight integrity.
A cross-sectional view of the neck ring of the Air Hat with the neck ring insert assembly inserted may be
visualized thus:
Seal No. 1 is provided by the neck dam (or dry suit yoke) pressed between the neck ring insert and the flat neck
ring gasket. The neck ring gasket is attached to the helmet neck ring with adhesive.
Seal No. 2 is provided by the large O-ring, which is pressed at its top against the shoulder of the neck ring, and
at its bottom against the lower surface of the channel in the brass neck ring insert. As the neck dam or dry suit
yoke age the material may compress necessitating the use of a shim to take up the additional space.
These two seals are different both in operation and effect. The flat neck ring gasket used in Seal No.1 is an
open-cell or sponge like material, which resists, but will not wholly prevent the passage of water. An open cell
material is used since it maintains its shape under pressure, at depth. So long as a positive air pressure is
maintained in the Air Hat no water will enter. Should the pressure in the Air Hat become negative, as when the
air is turned off and the diver inhales, a little water may enter. This can, however, readily be blown out through
the neck dam simply by closing the exhaust valve so that air is forced out through the neck dam. Seal No.2,
when adjusted properly, provides a completely watertight seal.
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