Monday, April 26, 2010

Crankcase explosion relief valve

In the name of Allah who is the most beneficient and merciful

As a practical safe guard against crankcase explosion relief valves or doors are fitted. These valves serve to relieve excessive crankcase pressures and stop flames being emitted from the crankcase. The cause of crankcase explosion is a “hot spot” resulting due to hot running bearing or any other overheated machinery part. In normal condition air in crankcase contains oil droplets and if these oil droplets will come into contact of a hot spot it will be vaporized and will form explosive oil mist. Regulation demands that for engines of over 300 mm bore, one crankcase relief valves is fitted to each crankcase and chain drive casing. Figure shows a crank case relief valve is fitted to diesel engine crank case. 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.

The valve spring is designed to allow the valve open under an internal pressure of approximately 5 KW/M2 and will close automatically when pressure has been relieved.

Crank case doors should be robust(determined) to prevent damages or rupture(break or burst suddenly) before relief valves operate to relieve pressure valves will required little maintenance but should be tested periodically by hand, the spring should be inspected and the guaze cleaned.

DATE: 24/OCT/2009
TIME: 09:55 AM