- Deck Main high Pressure Shutdown
- Differential Pressure Alarm Shut Down
- Atmospheric Vent Valve,
- Power Operated Deck Main Isolating Valve.
- Deck Main Non-Return Valve With Disc Position Indicator.
- Deck Seal Water Supply Low Pressure (or Flow) Alarm
- Ultrasonic Type Level Sensors
Proposed measures to reduce risk of backflow
The risk of hydrocarbon gas backflow can be reduced by modifying operating procedures to reduce or eliminate the need to operate the system in the manual tank pressure control mode. Provision of additional controls will enhance the safety of the dry type deck water seals. However, the cost of the additional hardware should be compared to the cost of changing the deck water seal to a different type (wet or semi-dry). The preferred solution would be to replace the dry deck water seal with another type.
Several proposed modifications, primarily relating to system sensors and controls, are listed below for consideration by operators if they desire to retain the dry type deck water seal. Some of the devices proposed may be utilised with other types of seals, as required by SOLAS for systems installed after 1981 (i.e. provision of a bleed to atmosphere valve), or as dictated by individual operator’s practices.
It is recognised that the additional instrumentation will increase the system complexity and overall maintenance. This, indeed, should be considered when deciding whether to modify the existing controls or to replace the deck seal with a new type. In either case, additional instrumentation will be required, for example, to replace or augment the deck seal level sensors.
