3.13.1 One or more liquid-filled pressure/vacuum
breakers should be fitted, unless pressure/vacuum valves having the
capacity to prevent excessive pressure or vacuum in accordance with
requirements of regulation 62.14 are
fitted.
3.13.2 These devices require little maintenance,
but will only operate at the required pressure if they are filled
to the correct level with liquid of the correct density. Either a
suitable oil or a freshwater/glycol mixture should be used to prevent
freezing in cold weather. Evaporation, ingress of seawater, condensation
and corrosion should be taken into consideration and adequately compensated
for. In heavy weather, the pressure surge caused by the motion of
liquid in the cargo tanks may cause the liquid of the pressure/vacuum
breaker to be blown out (see figure 16).
3.13.3 The designer should ensure that the characteristics
of the deck water seal, pressure/vacuum breakers and pressure/vacuum
valves and the pressure settings of the high and low inert gas deck
pressure alarms are compatible. It is also desirable to check that
all pressure/vacuum devices are operating at their designed pressure
settings.