TYPES. ADJUSTMENTS Fuel adjustments of a Diesel fuel pump are not of frequent occurrence, nevertheless, this particular part of the engine is of vital importance. The successful operation of a Diesel depends, in a great measure, upon the accuracy and reliability of the pumping mechanism. When it is considered that on a 100 h.p. cylinder, operating at 200 r.p.m. or 100 power strokes per minute, the volume of a single full-load fuel charge is less than .3 cubic inch, the necessity , of accurate pumping is apparent. Since the usual speed regulation require ment is 2 per cent. on each side of normal, the extreme variation that is permissible in the volume of a single injection at a given speed is .006 cubic inch. The pump, then, must be not only correct in design but also absolutely high-grade in the workman ship involved in its actual manufacture.
As has been previously outlined, two types of fuel injection are in use: the open- and the enclosed-nozzle type. The fuel pumps follow the same classification. First, the pumps on engines employing the closed-nozzle fuel valve must be constructed to resist a pumping head equivalent of more than 1000 lbs. per sq. inch. This demands rugged construction and absolutely leak-proof pump valves. The governor control, where the control is through the pump plunger, is called upon to withstand severe stresses. The open-nozzle fuel valve offers no pressure resistance to the pump discharge; consequently the pumping head consists of merely the pipe and check valve resistances, which are negligible. This fact enables the fuel pump to be designed with direct control of the pump plunger, with but slight reactions on the governor.
American Diesel.—The numerous American engines that are still in service are equipped with the Bagtrup governor and fuel pump, appearing in Fig. 135. The mechanism consists of a pump body in which reciprocates the plunger, one plunger for each engine cylinder, the plunger being driven by an eccentric mounted on the pump shaft. This shaft carries a gear which is actuated by a train of gears from the engine crankshaft. The suction valve is mechanically oper ated, by means of a bell-crank B and reach-rod A, from the plunger eccentric strap. The bell-crank
fulcrums on an eccentric shaft C controlled by the governor sleeve. The suction valve is opened during the suction stroke and part of the discharge stroke. If the load is heavy the fulcrum pivot is raised, allowing the suction valve to close early; the fuel then is forced out through the discharge valve into the fuel injection valve. On light loads the governor lowers the fulcrum, causing the suction valve to remain open for a greater part of the plunger stroke; the oil then passes back through the suction valve.
The reaction of the governor sleeve is heavy, and the speed regulation is not as close as is de manded in electric plants. In starting the engine a hand crank is provided, which allows the fuel line and injection valve to be charged before the engine is turned over.
Adjustments. Setting Suction Valve.—In setting the suction valve the governor should be blocked to the mid-position and the particular pump plunger placed on the upper dead-center. The suction valve lever should then clear the suction valve stem by 3z inch. This clearance can be secured by altering the length of the lever reach-rod A, which has turnbuckle ends.
Leaky Valves.—The suction valve, being of the poppet type, frequently leaks. The proper method of regrinding is to remove the valve and cage. Disassembling, the spring is removed and the valve coated with emery flour and vaseline and again placed in the cage. A nail thrust through the cotter opening makes a convenient handle with which to turn the valve.
Discharge Valves.—The discharge line has two ball valves. When the oil is clean and free from dirt, little trouble is ex perienced. The chief attention is given to the valve seats. These seats tend to wear rounded, making a poor seal. When the seat is in this condition, it should be reamed to the correct 45-degree angle; in this work the reamer must not chatter, or the seat will not be oil-tight. The lift of the valve should not exceed ;16 inch. If it is greater, the ball valve will be slow in seating and will allow part of the oil to flow back through the valve opening. With heavy oils the seating is so slow that a small helical spring becomes necessary.