PV breakers on ships are safety devices to protect the tanks from excessive pressure and vacuum. When pressure or vacuum is not maintained inside the tanks, this will activate the PV breakers, thus making the air and gas flow uncontrollable. Hydrocarbon vapors may escape to the deck and air may be drawn inside the tanks.

2.Operations of PV Breakers

There are three ways the PV breakers operate:

Normal operation– during normal operation, the relatively low inert gas pressure in the inert gas main line that has around 100 -200 mmAq will cause a slight displacement of water inside the PV breakers. In this manner, the water lock ensures that the normal pressure will not spread on the deck.

Over-pressure operation– the tanks will be over-pressurized due to some accidental closure of valves, the cargo filling rate is higher than the venting of the gas rate, and/or any failure of the control system. Once the over pressure setting is reached, the vapors inside the tank will push through the water in the PV breakers until it opens and releases the excess vapors along with the water. In addition, the PV breakers open up before the deck seal reaches it sealing limit.

Vacuum operation– due to some circumstances like the cargo discharge rate being higher than the gas supply rate and/or any reduction in ambient temperature, a vacuum condition will develop inside the tanks. Through this, PV breakers will open up, drawing air inside along with the sealing water.