OIL MIST DETECTOR : CONSTRUCTION WORKING AND MAINTENANCE

OIL MIST DETECTOR

AN OVERHEATED DIESEL ENGINE CAN BECOME A SOURCE OF FIRE AS IT CONTAIN ALL THE ELEMENT OF FIRE TRIANGLE. TO ENSURE ITS OPERATIONAL STABILITY PERIODIC MAINTENANCE AND PROPER PRACTICES HAVE TO BE FOLLOWED ON BOARD. OIL MIST IS CREATED IN THE CRANKCASE WHEN THE LUBRICATING OIL IS SPLASHED BY MOVING AND ROTATING POINT. THE MIST INSIDE CRANK CASE HAVE A LOWER FLASH POINT WHICH WHEN COMES IN CONTACT WITH HOTSPOT MAY RESULT IN FIRE. THUS IT IS IMPORTANT TO MONITOR THE CONCENTRATION OF OIL AND INCASE PRESENCE OF OIL MIST IS DETECTED THE ENGINE SHOULD BE STOPPED OR ITS SPEED LOWERED.

                                                                   OIL MIST DETECTOR ARE USED TO MEASURE THE AMOUNT OF MIST PRESENT IN THE CRANK CASE. EACH CYLINDER CRANKCASE IS CONNECTED TO AN OIL MIST DETECTOR WHICH CONTINUOUSLY CHECK THE AMOUNT OF MIST FROM EACH DETECTOR. THIS WILL GIVE ALARM IN CASE THE CONCENTRATION OF MIST IS FOUND TO BE INCREASED.

CONSTRUCTION

• OMD IS CONNECTED TO EACH CYLINDER IT HELPS IN DETECTION OF OIL MIST IF FORMED AND HAS NO ROLE IN REDUCTION OR PREVENTION OF MIST FORMATION.
• THE MOST COMMON ARRANGEMENT OF OIL MIST DETECTOR CONSIST OF TWO PARALLEL TUBES OF EQUAL SIZE. ONE IS REFERENCE TUBE AND THE OTHER IS SAMPLING TUBE.
• AT ONE END OF EACH TUBE A PHOTO ELECTRIC CELL IS PLACED.THIS PHOTO ELECTRIC CELL GENERATES A ELECTRIC CURRENT WHEN LIGHT FALLS ON THE SURFACE.
• THE AMOUNT OF CURRENT GENERATED IS DIRECTLY PROPORTIONAL TO AMOUNT OF LIGHT FALLING ON THE SURFACE.
• THE OTHER END OF EACH TUBE IS FITTED WITH A LENS THAT ALLOW LIGHT TO PASS THROUGH THEM.
• ONE OF THE TUBE HAS INLET AND OUTLET CONNECTION FOR INTRODUCTION OF OIL MIST.
• FAN IS PROVIDED FOR COLLECTION OF SAMPLE.

WORKING

• IF THE MIST IS FOUND IN SAMPLING TUBE THEN REFERENCE TUBE  WILL GENERATE MORE CURRENT ON PHOTO ELECTRIC CELL AS COMPARED TO SAMPLING TUBE THIS WILL RESULT IN TRIGGERING OF ALARM.
• SAMPLING TUBE HAS CONNECTION FOR OIL MIST, WHICH IS EXTRACTED FROM THE CRANK CASE WITH THE HELP OF EXTRACTOR FAN.
• THE REFERENCE TUBE IS FILLED WITH CLEANED AIR AND IS USED AS A REFERENCE FOR MEASURING THE LEVEL OF MIST.
• SAMPLE FOR EACH CYLINDER IS MONITORED BY USING A ROTATING SENSOR VALVE WHICH CONNECTS EACH CYLINDER IN SEQUENCE OF OMD.
• IF THE CONCENTRATION OF OIL MIST IS MEASURED IN TUBE RISES THE INTENSITY OF LIGHT REACHING THE PHOTO ELECTRIC CELL REDUCES.
• AS BOTH TUBE ARE ELECTRICALLY CONNECTED THE IMBALANCE OF GENERATION OF ELECTRIC CURRENT WHICH WILL LEAD TO TRIGGERING OF ALARM.
• WHEN OIL MIST IS DETECTED THE ROTATING SELECTOR VALVE IMMEDIATELY STOPS TO INDICATE THE CYLINDER WITH HIGHER CONCENTRATION.
• ON INDICATION OF ALARM ENGINE SHOULD SLOW DOWN OR STOP TO PREVENT FURTHER DAMAGE.

MAINTENANCE

• IT IS IMPORTANT TO CARRY OUT ROUTINE MAINTENANCE OF OMD TO PREVENT ANY FALSE ALARM.
• THE SENSITIVITY OF OMD MUST BE CHECKED ON REGULAR BASIS.
•  AS ALL SAMPLE CONTAIN A SMALL AMOUNT OF MIST, THE LENS MIRROR TENDS TO GET DIRTY AND THUS SHOULD BE REGULARLY CLEANED.
• THE EXTRACTOR FAN AND ROTATING VALVE SHOULD BE CHECKED TO AVOID CHOCKING OF A PARTICULAR TUBE.
• THE SAMPLING TUBES THAT CONNECT CYLINDER TO THE OMD SHOULD NOT HAVE ANY LOOPS AND ALSO SHOULD NOT BE OF LENGTH MORE THAN 12.5 METERS.