Pv valve and pv breaker have different functions.Let us Understand Difference between pv valve and over breaker from different points.
What is pressure vacuum (PV Valve ) and pressure vacuum (PV ) Breaker ?
PV Valve can be simply defined as a device used to maintain the pressure and vacuum in the cargo tank during loading and discharging, or it can also be described as a device for preventing the cargo tank from over and under pressure.
Pressure Vacuum Breaker which is also known as PV Breaker.
It is a safety devices which is used in IG Line on Deck.
Function of pv valve and Pv breaker
Functions of PV Valve
It is used to maintain the
- pressure and vacuum in the cargo tank during loading and unloading, or
- it can also be described as a means of preventing the cargo tank from over and under pressure.
The Functions of Pv Breaker are following:-
- Abnormal increase in pressure in cargo tanks when the required gas outlet rate is loaded
- Abnormal increase in pressure in cargo tanks when the cargo is discharged beyond the specified rate of inert gas blower
- Abnormal rise or drop in pressure in cargo tanks when the breather valve does not operate properly due to fluctuations in pressure in cargo tanks due to variations in atmospheric and temperatures of seawater.
On basis of operating pressure
Pressure vacuum valve operates at Water Column 1400 mm and at vacuum of -250 mm of water column.
PV Breaker operate at water column of 1600 mm to 1800 mm and at a vaccum of 400 mm of water column.
Note :- 0..0980665 bar = 1000 mm of water column.
Or we can take 1000 mm of water column =0.1bar
When and where Pv breaker and pv valve is used
Pressure vacuum valve
An individual PV Valve is fitted on each and every cargo tank.
The drop in pressure in the cargo tank causes the small valve to open downwards to equal internal pressure with external pressure and vice versa for overpressure.
Only one in line is fitted as we see in the figure above mentioned
High pressure increase due to constant fast rate of loading causes a rapid increase due to the explosion,the pv valve is not designed for this purpose.
Thus pv breaker is used where there is an abnormal increase in pressure in the cargo tank when loaded beyond the specified rate.
What pressure it maintains
Pv valve maintain pressure between 0.07 to 0.20 bar for large oil tankers.
Pv breaker maintain pressure even the pressure rise to 0.24 bar (maximum )