4. Lesson 4. Fuel system defects

Notes:

Derangements in the fuel system are most likely to occur at the fuel measuring pumps. These pumps must handle a very small amount of oil at high pressure on each stroke and in order to do this the suction and discharge valves must be kept in perfect condition. A frequent source of trouble with these valves is dirt or grit in the oil. A small particle of sand or a thread qf waste under a valve will cause it to leak. Good strainers should be provided in the fuel oil supply line to the pumps and the strainers should be cleaned frequently. The pump plungers should be very carefully packed to prevent leakage of oil outward and air inward. Accumu­lation of air in the pumps will cause either irregular supply of fuel to the engine or stoppage. Stoppage of fuel supply to any one cylinder throws extra load on the other cylinders when the governor acts to increase the pumps discharge. Repeated regrinding of the pump suction valves will require careful checking of the pump timing.

Combustion defects

Normally the combustion in each power cylinder should be smokeless and complete and occur early in the stroke. Insufficient breaking up of the oil during injection will cause slow and incomplete burning and may be the result of clogged fuel nozzles, oil too cold or incorrect timing. Other causes of incomplete burning are compression too low, injection valves not correctly timed and air inlet pipes clogged.

Cooling water system defects

Complete stoppage of the cooling water supply can hardly occur unless the circulating pump breaks down or the ship grounds in shoal water where mud may plug up the sea injection valve, thus stopping the supply of raw water to the coolers of a closed fresh water system or the jacket supply of a sea water cooling system. In the event of the rare occurrence of pump breakage there is always an auxiliary pump available. Most well designed ships, especially when designed to operate in shoal water, have high and low sea suctions. The high suction is used in shallow water where mud might be drawn in through the low suction. The low suction should always be used at sea as the rolling of the ship is likely to throw the high suction out of the water and admit air into the sys­tem. It not infrequently happens when ships anchor in tropical harbors that the sea suction becomes clogged with jellyfish. When this happens it can be cleared by blowing out, if a steam or air con­nection on the body of the sea valve is available.

Failure of the water supply to any individual cylinder or piston may be caused by an air pocket in the supply line to that point or in the upper part of the cylinder head. Where all of the cooling water is passed through the coolers on the air compressor before reaching the engine jackets a leak in a cooler will allow air to blow into the water and stop the supply to all cylinders.

Lubricating system defects

All Diesel engines today are lubricated by the forced feed method and no hand oiling of any part is required. This requires that the engine housings be closed in, to prevent loss of oil through splashing, and the oil piping, with the oil circulating pump, forms a closed circuit through which the same oil circulates repeatedly. Of course the most serious derangement in such a system is loss of pressure.