Pump Valves.—The pump valves are of the ball type. In case leaks develop, a hardwood stick can be placed on the ball and struck a light blow with a hammer. This will give the ball a new seat on the housing. In event the ball is scored or rough, the only remedy is replacement with a new ball; even here the ball must be given a new seat in the housing. The ball valve, if it has any great amount of lift, is sluggish in closing. A lift for a pump ball valve ought never to exceed MG inch. If more than this, a light coil spring should be inserted above the ball to quicken its action.
Timing the adjusting the pump plunger for no load and full-load strokes, the reach-rod A should be adjusted to allow the plunger to touch the wedge at the beginning of the wedge slope, when the governor is at its lowest position, which is the full-load condition. For no load, when the governor is blocked open, the wedge should have moved to a position where the plunger has a slight clearance between the slot edge and the wedge, on the inner position of the pump plunger.
Diesel Fuel fuel pump used on the Allis-Chalmers engine is shown in Fig. 142. The pump plunger is actuated, through a rock-shaft D and the con nection rod C, by the fuel cam below the pump. The plunger rock-shaft D is fulcrumed at E on the lever F, which is under control of the governor through the reach-rod G. As the engine speeds up, the reach-rod moves downward; this raises the ful crum pivot E. This motion of the fulcrum raises the pump plunger A until its end is above the by-pass slot H at the end of the suction stroke since the plunger spring holds the rod C in contact with the cam B. As the cam rotates, the plunger receives a constant stroke, but, since part of the stroke occurs before the by-pass slot is covered by the plunger, the first portion of the oil displaced by the plunger flows through the slots H. As soon as the plunger passes the slots, the oil below the plunger is forced through the discharge valve to the atomizer. Since an open-nozzle fuel valve is employed in connection with the pump, the latter has but the pipe resistance to overcome. The governor, then, is called upon to oppose only a slight reaction and consequently can be sensitive without danger of hunting.
The cam connection rod C is provided with a special head having adjusting set-screws. Proper manipulation of these set-screws will alter the. effective stroke of the pump plunger.
In stopping the engine the hand lever is raised, allowing the release band J to grip the lock I on the rod C. This prevents the rod from dropping into contact with the cam. In starting, the handle is used to prime the pump.
The pump is fitted with a plunger and rocker mechanism for each cylinder of engine, with individual cams on the layshaft.
De La Vergne FD Diesel Fuel Pump.—Figure 143 is an external view of the fuel pump used on the FD engine. The governor acts upon a by-pass valve a through a system of levers. The fuel charges are controlled by the movement of this by-pass valve.
Nelseco Marine Diesel Fuel fuel pump fitted to the Nelseco Marine Diesel appears in Fig. 144. The engine speed can be altered by the control lever shown, through a linkage which alters the position of the governor lever fulcrum. The governor then maintains this desired speed by changing the period of suction valve opening. The fuel pump consists of the working plunger driven by an eccentric, and the suction and discharge valves. The suction valve is held open through over until some two plungers are at the inner end of their stroke. Then adjust the adjusting screw on the corresponding suction valves until a piece of paper placed between the adjusting screw point and the fuel suction valve end is just barely held. Adjust all the other suction valves in the same way, still keeping the fuel control handle locked in the same place.
National Transit Diesel Fuel fuel pump on the first National Transit engines has a differential plunger, the upper end being hollow and provided with a cut-off valve, Fig.
145. This differential plunger is driven by an eccentric keyed to the camshaft. The cut-off valve is under control of the governor through a link and bell-crank. The pump functions as follows: On full load the governor sleeve is as shown in the figure; this position is such that the cut-off valve leaves its seat on the plunger as soon as the latter starts on the downward or suction stroke. The oil is then drawn through the suction valve and fills the passage in the plunger and the chamber A above the differential plunger. On the upward or discharge stroke, the cut-off valve being open, the large end of the plunger 'displaces the oil in this chamber and forces it down through the plunger and out the discharge valve. On low loads the governor bell-crank moves downward; this allows the valve to remain seated on the plunger during part of the downward stroke. As soon as the plunger moves below this point, the valve rests on the bell-crank fingers and leaves its seat. The chamber fills with oil, and on the upward stroke the fuel is forced out the discharge valve until the plunger comes in contact with the cut off valve. The cut-off valve then seats, and all the oil displaced by the further movement of the plunger passes out through the overflow valve B at the top of the pump body.