21.Crankcase relief door

IMO SOLAS Chapter II-1 and IACS Unified Requirements

1.Crankcases for engines having a cylinder bore greater than 200 mm and above or having a crankcase gross volume exceeding 0.6m3 are to be provided with explosion relief valves.
2.Crankcases for engines having a cylinder bore exceeding 300 mm are required to have at least one crankcase explosion relief valve at each crankthrow.
3.An additional explosion relief valve is required on separate crankcase spaces such as gear or chain cases for camshaft drives where the gross volume exceeds 0.6m3
4.The free area of each crankcase relief valve is to be not vi. less than 45cm2.
5.The combined free area of all crankcase relief valves is to be not less than 115cm2 per m3 of crankcase gross volume.
6.Crankcase explosion relief valves are required to open quickly at an overpressure not exceeding 0.2bar in the crankcase and close quickly to avoid inrush of air into the crankcase following an explosion.
7.Crankcase explosion relief valves are required to be of an approved type.
8.The discharges from crankcase explosion relief valves are to be shielded to reduce the possible danger from emission of flame during an explosion.


Because the valve must be fully open at 0.2 bar, it will start to open at pressures well below this ( as the spring is compressed, the force required to open the valve increases). Typical opening pressure is about 0.05 bar

Function

• To relieve excess pressure inside the crankcase thereby normalizing the pressure
• To prevent the flames inside the crankcase from coming out and causing further damage

Testing of crankcase relief valve

When engine is stopping, after removing the flame trap and press up the valve disc and check the action of opening and closing. The valve must be opened smartly and closed positively and rapidly. The valve must be oil and gas tight. When the engine is running we must only check the oil leakage that the v/v is seal or not.

It consists of a light spring loaded non return disc valve of simple construction. The valve disc is of  aluminum alloy which reduces its mass and the inertia to be overcome when opening or closing valve rapidly. The large “diameter” light spring holds the valve closed against its seat. The valve landing must make a gas and oil tight seal when closed and a nonstick oil and heat resisting rubber ring is fitted to the disc face. A deflector is fitted on the outside of  the engine to safeguard personnel from the out flowing gases, an inside the engine, other valve opening, and oil wetted gauze acts as a flame trap to stop any flames leaving the crank case after operation the valve will close automatically under the action of the spring. When wet with oil the gauze dissipated heat at greater rate and become more effective as a flame trap.