Figure 5-17. Pressure-Times Gear Pump.
operator to manually control engine speed above idle as
shutdown valve through a supply line into the lower
required by varying operating conditions of speed and
drilled passage in the cylinder head at the front of the
load. In the PTG pump, fuel flows through the governor
engine. A second drilling in the head is aliened with the
to the throttle shaft. At idle speed, fuel flows through the
upper injector radial groove to drain away excess fuel.
idle port in the governor barrel, past the throttle shaft.
A fuel drain at the flywheel end of the engine allows
To operate above idle speed, fuel flows through the main
return of the unused fuel to the fuel tank. There are four
governor barrel port to the throttling hole in the shaft.
phases of injector operation:
Metering (A, Fig.
(4) The fuel shutdown valve is located on top of
the fuel pump. It shuts off fuel to the injectors. With
begins with the plunger just beginning to move
the master switch on, the solenoid opens the valve.
downward and the engine is on the beginning of the
With the switch off, the spring loaded valve returns to the
compression stroke. The fuel is trapped in the cup, the
OFF position. In case of an electrical failure, rotation of
check ball stops the fuel from flowing backwards, and
the manual knob clockwise will permit fuel to flow
the fuel begins to be pressurized. The excess fuel flows
through the valve. The knob is located on the front of
around the lower annular ring, up the barrel, and is
c. PTD Injectors. A PTD injector is provided at
(2) Prelnjection (B, Fig. 5-18). The plunger is
each engine cylinder to spray the fuel into the
almost all the way down, the engine is
combustion chambers. PTD injectors are of the unit
type, operated by an engine-based camshaft.
flows from a connection at the top of the fuel pump