The Multiple Unit Injection Pump.

that is tailored to provide the best overall performance for their

particular application.

(2) The Multiple Unit Injection Pump.

(a) The multiple unit injection pump contains an individual

plungertype injector pump for each cylinder. These pumps are arranged in a

line so that they may be driven by a common camshaft. The lobes of the

camshaft are arranged so that they operate the injection pumps in a sequence

that coincides with the firing order of the engine. This camshaft is driven

by the engine, through gears, at a speed of exactly onehalf that of the

crankshaft. This exact speed is maintained so that the injectors will each

deliver their fuel charge at the beginning of their respective cylinder's

power stroke. Power strokes occur during every other crankshaft revolution

in a fourstroke cycle diesel engine.

(b) Excess fuel flows from the injection pump through the relief

valve and back to the fuel tank. The relief valve usually is adjusted to

open at approximately 15 psi.

(c) The pumps consist of a finely fitted plunger that is actuated

by the camshaft against the force of the plunger spring. The bore that the

plunger rides in has two passages machined into it. One of these passages

is the delivery port, through which the pump is filled. The other passage

is the spill port, through which excess fuel is discharged. When the

plunger is fully in its return position, fuel flows into the pump cavity

through the uncovered delivery port and out of the pump cavity through the

uncovered spill port. The

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