Deck seals are a safety device fitted on oil tankers to prevent explosive hydrocarbon vapours to travel from the Cargo area to the Engine area (where the sources of Ignition are present.)
In other words, the back draft of gas picks up the water in the deck seal up the return line and it is the weight of the water column that prevents the gas from going to the flammable area. As a result, the deck seal needs to be big enough to accommodate the quantity of water required.
Purpose of deck seal:
The purpose of the deck water seal is to prevent feedback of hydrocarbon gases from the cargo tanks via the inert gas deck main to the engine room and boiler uptake. A small leakage of hydrocarbon gas can built up to a dangerous concentration over a period of time. Since a mechanical non return valve will permit a very slIGht leakage, it is necessary to provide a liquid seal. The deck water seal is manufactured in mild steel and is internally coated with glass flake.
what is the deck seal pressure?