User manual

Poseidon MKVI User Manual
Chapter 1
Page 9
in the CO
2
absorbent cartridge lid. Axial o-rings are laid into an annular groove in the body of
the object to be sealed.
The object is then pressed perpendicularly agains a at, clean sealing surface. The axial o-ring
is then compressed along its top side by the at mating surface and compressed into the
groove. This compression of the o-ring causes it to seal against the sides of the groove and to
the at mating surface. Because a release of the mating pressure would result in a leak in a
face type seal, these require a securing mechanism that not only prevents the part from lifting
off accidentally, but also actively compresses the axial o-ring against the at mating surface. In
the case of the CO
2
cartridge, the cartridge end plate is equipped with four thumb screws to
secure it in place and tighten it down.
A second, and more commonly used seal is the “ radial “ o-ring. Figure 1-11 shows a typical
implementation in the Poseidon MKVI breathing hose and hose connection ports. In contrast
to a axial o-ring seal, a radial seal involves a circular groove that goes around a cylindrical or
semi-cylindrical object (it can be a rectangular object with rounded corners provided the
corners have a sufciently large radius – an example of this is the Electronics Module dual
radial seals). In a radial seal, the groove is designed such that the o-ring snaps into the groove
with a certain pre-tension. Once seated the o-ring cannot leave the groove. To complete the
seal, the side of the connection containing the radial o-ring and groove is inserted into a cylin-
drical receiving surface. As the o-ring is inserted, the cylindrical surface uniformly compresses
the radial o-ring and creates the seal against all contacting surfaces. The important distinction
is that with a radial seal it is possible to rotate the objects relative to one another and still retain
a good waterproof seal. This is the reason the breathing hoses use radial seals, for example
– so that you can adjust their positions and that of the mouthpiece without having to make and
break the connections.
Radial o-ring seals still require a retainer to prevent them from accidental disassembly during
diving. For hose connections we use rotating shells whose threads engage a capture thread
on the mating part (see Figure 1-11 for example).
For face and radial o-rings to properly work, the diver is responsible for ensuring the
following:
• The o-ring is clean and free of debris and scratches (no cuts, gouges, dust, dirt, sand, hair, etc.)
• The o-ring is lubricated with an approved o-ring grease.
• The sealing surfaces are clean and free of debris, scratches and gouges.
• The sealing surfaces are lubricated with an approved o-ring grease.
• The retainer mechanism (e.g. hand screws, hand nuts, or threaded shells) is securely
in place.
”Radial” o-ring seal
Sealing surface for ”radial” o-ring seal
Retainer nut capture thread
Figure 1-10.
Typical “ Face “ type o-ring seal.
Figure 1-11. Typical “ Radial “ type o-ring seal.
“ Face “ o-ring seal