The IMO requirement on Tanker Safety and Pollution Prevention, Annex I - Regulation 13B (requirement for C.O.W.) and its Resolution A.446 (XI), 6.6(b) (use and control of Inert Gas) states "during Crude Oil Washing, the pressure of the atmosphere at the tank is no longer positive, the washing must be stopped until satisfactory conditions are restored."

The C.O.W. Operation / Control for this requirement can be judged by fitting portable gas pressure meter on MMC Tank Gauging Station (Vapor Locks) and watch condition of inert gas pressure level on each tank.

MMC Inert Gas Pressure Meter Model. "GVP-75" series consists of a pressure meter (Low measuring meter) on a gas seal attachment, it can be fitted on MMC Tank Gauging Station (Vapor Locks) in order to prevent leakage of inert gas from tank.

The pressure meter contains a screw type orifice which controls sudden change of pressure.
Also a Mesh Filter is fitted at the inlet of gas pressure to prevent dust coming in.
Indication of the meter applies within the range -10kPa (vacuum) ~ +30kPa (pressure).

This portable gas pressure meter is developed to measure pressure of Inert-Gas filled in tank simply on deck of each tank locally. However, as the meter is very low indication mechanical and delicate pressure type, So, careful handling is required. Also the meter is not constructed for water-tightness and durability to fit on deck permanently. It is recommended to remove it from tank gauging station and store to ship's cabin after use.