WHAT IS CRANKCASE RELIEF VALVE, HOW TO PRESSURE TEST IT, REGULATION REGARDING RELIEF DOOR

CRANKCASE RELIEF VALVE

• AS A SAFE GUARD AGAINST CRANKCASE EXPLOSION CRANKCASE RELIEF VALVE AND DOORS ARE FITTED. THESE VALVE SERVE THREE FUNCTIONS

1. TO RELIEVE THE EXCESS PRESSURE FROM THE CRANKCASE AND THUS NORMALISING THE PRESSURE INSIDE THE CRANKCASE.
2. TO PREVENT FLAME INSIDE THE CRANKCASE FROM COMING OUT AND THUS PREVENTING ANY FURTHER DAMAGE.
3. IT ALSO WONT ALLOW FLAME FROM OUTSIDE TO COME IN BECAUSE OF FLAME ARRESTER.

IN SULZER ENGINE OPENING PRESSURE IS 0.2 BAR ABOVE ATMOSPHERE PRESSURE AND IN MAN B&W OPENING PRESSURE IS 0.05 BAR ABOVE THE ATMOSPHERE PRESSURE.

OPENING PRESSURE OF CRANKCASE RELIEF DOOR

• TO MEASURE THE OPENING PRESSURE WE HAVE A SPRING SCALE AND ROD WHICH ARE FITTED ON THE CRANKCASE DOOR PULLING THE ROD WE WILL GET A READING ON SPRING SCALE THAT INDICATE AT WHAT FORCE IT WILL OPEN.
• AS WE GET READING FROM SPRING SCALE IN KGS TO OBTAIN THE PRESSURE 

PRESSURE= FORCE/ AREA                

                                                  FORCE= VALUE OF FORCE FROM SPRING SCALE

                                                  AREA= AREA OF DOOR GIVEN IN MANUAL.

A DEFLECTOR IS FITTED OUTSIDE THE ENGINE TO SAFEGUARD PERSONNEL FROM THE OUT FLOWING GASES AND INSIDE ENGINE OVER THE VALVE OPENING AN OIL WETTED GUAZE OR FLAME ARRESTER ACTS AS A FLAME TRAP TO STOP ANY FLAMES LEAVING THE CRANKCASE. AFTER OPERATION THE VALVE WILL CLOSE AUTOMATICALLY UNDER ACTION OF SPRING.

REGULATION REGARDING RELIEF DOOR

• THE INTERNAL COMBUSTION ENGINE OF A CYLINDER DIAMETER OF 200 MM OR A CRANKCASE VOLUME OF 0.6 METER CUBE AND ABOVE SHALL BE PROVIDED WITH CRANKCASE RELIEF VALVE OF SUITABLE TYPE AND WITH SUFFICIENT RELIEF AREA.
• IN SMALL ENGINE WHERE DIAMETER DOES NOT EXCEED 300 MM THE CRANKCASE DOOR ARE USUALLY STRONG AND THUS IT HAVE RELIVE VALVE AT ITS END.
• IN LARGE ENGINE WHERE CYLINDER DIAMETER IS OVER 30 CM, IT IS REQUIRED TO HAVE ONE RELIEVE  VALVE  PLACED ON EACH CRANKCASE DOOR.
• ITS FREE AREA SHOULD NOT BE SMALLER THAN 45 CM SQUARE AND SHOULD BE MINIMUM 115 CM SQUARE PER METER CUBE OF GROSS CRANKCASE VOLUME.
• SPRING SETTING FOR OPENING PRESSURE IS 0.07 BAR AT AN INTERNAL PRESSURE AND WILL CLOSE WHEN THE PRESSURE HAS BEEN RELIEVED.