McIntosh & Seymour Marine Diesel Fuel The Four stroke-cycle Marine Diesel of this make is equipped with a fuel pump along somewhat similar lines. In this pump, Fig. 139, six plungers, placed horizontally, are operated by eccentrics mounted on eccentrics. This second set of eccentrics is keyed to the pump shaft, which is moved lengthwise by means of the manual control lever. These eccentrics are made with their axes at angles with the eccentric shaft center line. Shifting the shaft lengthwise increases or decreases the travel of the pump plungers; the travel of the plungers can be completely cut out by reducing the eccentric throw to zero. The longitudinal movement of this pump shaft is accomplished by the control lever through the air starting control shaft, as has been discussed in Chapter VIII. As a precaution against overspeeding, a governor is mounted on the pump shaft in the extension case of the pump and operates, through a linkage, a small shaft A, which raises the suction valves. In order to allow a single cylinder to be cut out at will, a hand lifter is provided for each suction valve. Another feature of excellence is the glass cup on the fuel suction line. This shows when the line is empty. To prime the engine when the engine is stopped, a handwheel is placed on the pump shaft, a few turns of which fills the suction line and pump cavities.
Fuel Pump Timing.—For each cylinder, the pump plunger must be at the end of its delivery stroke when the piston for that particular cylinder is at bottom dead-center, just beginning the compression stroke. The linkage to the control lever must be adjusted to give the pump plungers zero travel when the con trol lever is at both the start and stop positions.
McEwen Diesel Fuel Pump.—The McEwen Diesel has an open-nozzle fuel valve; consequently the pump is a departure from the designs already discussed. As will be noted in Fig. 140, the pump, for a single-cylinder engine, consists of a plunger housing, to which is bolted the valve body, and the pump plunger with actuating mechanism. In action the cam, through the rocker D, moves the pump plunger E to the left, which action forces the fuel charge out through the discharge line to the fuel injection valve. As the cam in turning releases the thrust on the rocker, the plunger spring forces the plunger to the right; this draws in a charge of oil through the suction valve. The pump plunger on this stroke moves to the right until it strikes the governor wedge C. The length of the plunger stroke deter mines the amount of oil entering the cylinder. The governor is linked to the wedge C and, as the engine speeds up, shoves the wedge farther in, decreasing the distance from the wedge to the face of the plunger slot. This reduces the plunger stroke.
This pump is one of the simplest in use and has the advantage, as have all wedge-governored pumps, of offering but slight re sistance to any governor movement. The reaction on the wedge
is merely that due to the plunger spring tension when the wedge is in contact with the plunger. This is slight and occurs only at the point of extreme suction travel of the plunger. As a consequence, the governor can be light and extremely sensitive. This is of distinct advantage in alternating-current work, or in any other work necessitating close regulation.
Pump Valves.—Both suction and discharge valves are of the poppet wing type with seats having a 60-degree slope. In regrinding these valves, the discharge valve must not be lowered enough to prevent a proper lift of the suction valve; this should be at least .03 inch, while the discharge lift works best with a lift of around inch.
Pump Plunger.:—The plunger has no stuffing-box, being pro vided with sealing grooves. Since the pumping head is very low, but little leakage will occur even though the pump sleeve is considerably worn.
Pump Timing.—The pump cam is keyed to the engine lay shaft and requires no alteration in timing. However, the pump plunger should be at the end of its discharge stroke when the engine piston is on out dead-center, just starting the compression stroke.
In setting the governor wedge for no-load conditions, after the weights are thrown out to their greatest travel, the wedge should be moved in until the slot is in contact with the thickest part of the wedge. Then after throwing the pump plunger to the end of its discharge by turning the engine over, there should be not more than .01-inch play between the wedge and the inner edge of the slot. This is the position of the wedge when no fuel is pumped. For full-load condition, at event the weight arms are at their maximum position, the wedge should have moved in the slot so that the slot edge just strikes the wedge at the point where the wedge slope begins. This point should be 2h inches from this first or no-load position.
Snow Diesel Fuel Pump.—The Snow Diesel engine has a fuel pump designed with wedge control. This pump, which appears in Fig. 141, has the plunger in two sections. The driving end of this plunger is hollow and carries the slot for the wedge. It is also provided with a pin which bears against the cam lever roller at all times, being held by a, compressed spring. With this design, on short plunger strokes, as on low load, the roller does not strike the plunger end when traveling at maximum speed. Instead the plunger pin moves in, being resisted by the spring, until the spring compression overcomes the pump plunger resist ance. At this point the pump plunger starts on the delivery stroke. The result is a quiet pump with a minimum of wear and shocks on the mechanism. The plunger wedge is fastened to the reach-rod A, which is under control of the governor.