TRUCK SERVICE MANUAL
2. It cuts off fuel to the injectors above maximum rated
3. Shaft (9) and its bore form, a fuel by-pass valve.
This shaft and bore allows or, restricts fuel flow.
During operation between idle and maximum speeds,
4. The shaft and sleeve are by-passing fuel when arm
fuel flows through the governor to the injectors. This fuel
(10) of lever is resting against adjusting screw (1). The
is controlled by the throttle and limited by the size of the
amount of fuel by-passed is adjusted by this screw,
idle spring plunger counterbore. When the engine
which protrudes from bottom of aneroid.
reaches governed speed, the governor weights move the
5. The lever arm connected to piston (8) by actuating
governor plunger, and fuel passages to the injectors are
shaft (6), rotates shaft; closing valve port. The lever is
shut off. At the same time another passage opens and
rotated by action of air intake manifold pressure against
dumps the fuel back into the main pump body. In this
piston and diaphragm (7), moving actuating shaft
manner, engine speed is controlled and limited by the
downward against resisting spring force.
governor regardless of throttle position.
6. Anytime engine intake manifold air pressure is above
preset "air actuation pressure", the aneroid is ineffective.
7. The aneroid begins dumping when intake manifold
pressure drops below preset value as happens after
The aneroid control, Fig. 5-7, provides a fuel by-pass
deceleration in traffic, deceleration during gear shifts,
system that responds to air intake manifold pressure and
down grade motoring with closed throttle or down grade
is used for close control of exhaust smoke.
operation on light load portion of governor droop curve.
8. The aneroid does not by-pass fuel under full throttle
turbocharger speed (intake manifold pressure) change
lug down conditions until speed is low enough to reduce
inherently lags behind the power or fuel demand
intake manifold air pressure to aneroid operating range
exercised by opening of the throttle. This lag does not
(usually below engine stall-out speed).
exist in the fuel system; therefore, an overrich or high
9. Fuel allowed to pass through by-pass valve is
fuel to air ratio, usually accompanied by smoke, occurs
returned to suction side (inlet fitting) of PT gear pump.
until the turbocharger "catches up".
The by-passed fuel reduces fuel pump out-put to engine
The function of the aneroid is to create a lag in fuel
and reduces fuel manifold pressure in proportion to the
system so response is equivalent to the turbocharger,
thus controlling engine smoke level.
PT (type D) Injectors
Aneroids must not be removed,
The injector provides a means of introducing fuel into
disconnected or otherwise rendered ineffective, nor
should settings be altered to exceed specifications
metering, timing and injection. Principles of operation
as set at the factory, see "Maintenance Schedule".
are the same for inline and V-engines but injector size
and internal design differs slightly. Fig. 5-11 illustrates
injectors used on the NTC-290 Engine.
Fuel supply and drain flow are accomplished through
internal drillings in the cylinder heads Fig's. 5-1. A radial
groove around each injector mates with the drilled
passages in the cylinder head and admits fuel through an
adjustable (adjustable by burnishing to size at test stand)
orifice plug in the injector body. A fine mesh screen at
each inlet groove provides final fuel filtration.
The fuel grooves around the injectors are separated by
"O" rings which seal against the cylinder head injector
bore. This forms a leak-proof passage between the
injectors and the cylinder head injector bore surface.
Fig. 5-7, (F5244). Aneroid cutaway
Fuel flows from a connection atop the fuel pump shut-
down valve through a supply line into the lower drilled
Fuel Flow (Aneroid)
passage in the cylinder head. A second drilling in the
1. Fuel from the fuel pump enters aneroid and is
head is aligned with the upper injector radial groove to
directed to starting check valve area (5, Fig. 5-7).
drain away excess fuel. A fuel drain allows return of the
2. The starting check valve (3) prevents aneroid from
unused fuel to the fuel tank.
by-passing fuel at engine cranking speeds. For speeds
above cranking, fuel pressure forces the check valve
open, allowing fuel to flow to valve port (4) or shaft (9).