Below you will find some common terms and definitions that will help you better understand your fuel system.

Acceleration Smoke Limiter
A device which limits the smoke of a diesel engine during acceleration by temporarily limiting the amount of fuel injected into the engine cylinders during speed and load transients below a steady-state limit.

Calibration
Fixing fuel delivery and speed adjustments to specified engine requirements. The setting of the delivery of an injection system.

Control Rack (rod)
The rack or rod by means of which the fuel delivery is regulated.

Delivery Valve
A valve installed in a pump, interposed between the pumping chamber and outlet, to control residual line pressures and which may or may not have an unloading or retraction function.

Delivery Valve Holder
A device which retains the delivery valve within the pump.

Distributor Pump (rotary pump)
An injection pump where each metered delivery is directed to the appropriate engine cylinder by a distributing device.

Excess Fuel Device
Any device provided for giving an increased fuel setting for starting only, generally designed to restore automatically action of the normal full load stop after starting.

Full Load Stop
A device which limits the maximum amout of fuel injected into the engine cylinders at the rated load and speed specified by the engine manufacturer.

Hydraulic Governor
A mechanical governor having a hydraulic servo-booster to increase output force.

Injection Lag
The time interval (usually expressed in degrees of crank angle) between the nominal start of injection pump delivery and the actual start of injection at the nozzle.

Injection Timing
The matching of the pump timing mark, or the injector timing mechanism, to some index mark on an engine component, such that injection will occur at the proper time with reference to the engine cycle.

Injection advance or retard
is respectively an earlier, or later, injection pump delivery cycle in reference to the injection cycle.

Inlet Metering
A system of metering fuel delivery by controlling the amount of fuel entering the pumping chamber during the filling or charging portion of the pump's cycle.

In-line Pump
An injection pump with two or more pumping elements arranged in line, each pumping element serving one engine cylinder only.

Mechanical Governor
A speed sensitive device of the centrifugal type, which controls the injection pump delivery soley by mechanical means.

Nozzle
The assembly of parts employed to atomize and deliver fuel to the engine.

Nozzle Opening Pressure
The pressure needed to unseat the nozzle valve.

Peak Injection Pressure
The maximum fuel pressure attained during the injection period (not to be confused with opening pressure).

Pilot Injection
A small initial charge of fuel delivered to the engine cylinder in advance of the main delivery of fuel.

Plunger & Barrel Assembly (P&B)
The combination of a pump plunger and its barrel constituting a pumping element. The P&B assembly may also perform the addtional functions of timing and metering.

Pneumatic Governor
A governor operated by a change in pressure created by the air actually consumed by the engine. A governor operated by air displaced by a device provided for this particular purpose and driven by the engine.

Port and Helix Metering
A system of metering fuel delivery by means of one or more helical cuts in the plunger and one or more ports in the barrel. Axial rotation of the plunger alters the effective portion of the stroke by changing the points at which the helices close and/or open the port(s).

Sac Hole
The recess immediately within the nozzle tip and acting as a feeder to the spray hole(s) of a hole-type nozzle.

Secondary Injection
The fuel discharged from the nozzle as a result of a reopening of the nozzle valve after the main discharge. (This is bad.)

Sleeve Metering
A system of metering fuel delivery by incorporating a movable sleeve with which port opening and/or port closing is controlled.

Spray Angle
The included angle of the cone embracing the axis of the several spray holes of a multihole nozzle. More than one spray angle on a single nozzle may be used.

Supply Pump (lift pump)
A pump for transferring the fuel from the tank and delivering it to the injection pump.

Torque Control
A device which modifies the maximum amount of fuel injected into the engine cylinders at speeds below rated speed to obtain the desired torque output.