3.7.1 The material used in the construction of
the nonreturn devices should be resistant to fire and to the corrosive
attack from acids formed by the gas. Alternatively low carbon steel
protected by a rubber lining or coated with glass fibre epoxy resin
or equivalent material may be used. Particular attention should be
paid to the gas inlet pipe to the water seal.
3.7.2 The deck water seal should present a resistance
to backflow of not less than the pressure setting of the pressure/vacuum
breaking device on the inert gas distribution system and should be
so designed as to prevent the backflow of gases under any foreseeable
operating conditions.
3.7.3 The water in the deck seal should be maintained
by a regulating flow of clean water through the deck seal reservoir.
3.7.4 Sight glasses and inspection openings should
be provided on the deck seal to permit satisfactory observation of
the water level during its operation and to facilitate a thorough
survey. The sight glasses should be reinforced to withstand impact.
3.7.5 Any drains from the nonreturn devices should
incorporate a water seal in accordance with 3.15.4 and
should comply generally with 3.16.