A cargo tank on any vessel has various safety settings/ features which enhance the overall safety of the operation. These are mandatory by the SOLAS convention and can be found in the original editions of SOLAS.
The various safety features of a cargo tank in a chemical or oil tanker are as follows:
PV Valves
These are used to release excess pressure from cargo tanks. Also, these come into play when the tank pressure falls below a set limit into the vacuum side. After its set limit is reached, these valves operate automatically and release the excess pressure into the atmosphere and while on the vacuum side, these take in some air from the atmosphere to keep the tank from getting into further vaccum state and crumbling under that pressure.
PV breaker
If for some reason, the PV Valve does not operate, the PV breaker lifts up automatically after its set value is reached either on the pressure side or on the vaccum side. It’s set values are a little higher than that of PV valve as guided by SOLAS.
Tank sensors
Every cargo tank has individual sensors which take various data like pressure, temperature, ullages from the cargo tank and show these on a screen in the CCR. Various high/low level alarms can be set up for these sensors to notify the duty officer when and if the value goes above or below the set values.
Mast Riser
This is connected to all the tanks and can be operated hydraulically from the CCR as well as from locally by a valve. This comes into play when the PV Valve fails and does not operate automatically.
