4. DOOR AND CLOSURE HINGES.
a.
Heavy doors and closures should be supported on compound action
hinges with antifriction bearings and precision adjustments.
(1) Compound hinges, Figure 3-26, allow the door or closure to
close with more uniform gasket compression than simple hinges.
(2) Antifriction bearings permit easy door or closure movement by
hand.
(3) Precision adjustments permit obtaining and maintaining proper
door position and alignment of sealing surfaces.
(4) Vertically opening doors or closures should have their mass
counterbalanced by counterweights or springs to prevent slamming when the
door or closure is lowered.
5. SEALS FOR CLOSURES AND DOORS. The seals for hyperbaric chamber doors and
closures fall into two main classes: mechanically energized and pressure
energized. Mechanical seals are clamped and compressed by the locking
mechanism. Their sealing preload is independent of the pressure, so they
must always be compressed sufficiently to seal the maximum rated pressure of
the system. Mechanical seals generally employ Neoprene rings or rectangular-
section gaskets.
Pressure energized seals derive their sealing compression from the
pressurized gas in the chamber. They are usually installed with a very light
preload and the sealing force increases as the retained pressure increases.
The seals take a variety of proprietary forms, most commonly involving a thin
lip which is forced against a flat surface as pressure builds up in the
chamber. Pressure energized seals are sometimes initially compressed by
pressure from an outside source, after which they become self-sustaining.
a. Closure Seals.
(1) Mechanically energized seals are usually flat or rectangular
section and must be clamped with considerable force to maintain their seal
when pressurized. The plain gasketed flange shown at Figure 3-27 must have
sufficient tension developed in the bolts so that when the internal pressure
mechanically deforms the system, the remaining clamping force on the gasket
is still great enough to maintain the seal.
(2) The flat gasket seal can be improved by retaining the gasket
in a slight recess, then if the pressure moves the gasket radially it stops
at the rim and becomes pressurized. See Figure 3-28.
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