六、THE SELECTION OF THE CF-ISO HIGH-VELOCITY RELIEF VALVE
CF-ISO high-velocity relief valve, complete in specifications。
The working pressure and the flow rate of the high-velocity relief valve for pipeline of liquid cargo tank shall meet to requirements of ship design. Tf its flow rate is too low, the tank may over pressure or lost pressure; if the flow rate is too high, the valve may be crashed.
ISO 15364 standards required data of flow rate shall be showed in graph or table, especially when it reaches to 1.1, 1.2 or 1.5 times of opening pressure for pressure valve, and it reaches to 1.1, 1.2, 1.5 or 2.0 times for vacuum valve.
The lowest working pressure and flow rate of pressure valve and vacuum valve is the lowest pressure and flow rate for working of valve.
Usually, the best working pressure for pressure valve and vacuum vavle are opening pressure or between 1.2 times of opening pressure, the best flow rate also in this range.
The opening pressure and flow rate shall meet to the requirements of ship design, if the diameter of outlet for CF-ISO high-velocity relief valve is keep the same.
Formula for diameter of high-velocity relief valve：
Diameter of high-velocity relief valve,
D is the diameter of pipeline or the diameter of high-velocity relief valve（mm）;
Q is the loading and discharging rate of each hour for ship design（m3/h）;
The flow of liquid cargo and the flow of valve are the flow of standard airs.
1、according to requirements, the escaped gas during loading shall more than 1.25 times of loading/discharging, which is maximum gas transmission rate;
2、1.48 times of density of gas from liquid and cargo mixture shall be considered by the suggestion of valve manufacturer; at least 1.05 times of pipeline resistance shall beselected;
3、calculation of diameter for breather pipeline, the velocity of escaped gas for relief valve is 40m/s by the suggestion of valve manufacturer.