User Manual

Pre-Injection
Cross section of pre-injection cycle
(2) Armature spring
(3) Armature
(4) Seated pin
(5) Spool spring
(6) Spool valve
(8) Intensifier piston
(10) Plunger
(16) Check piston
(19) Nozzle check
The injector is in the phase of pre-
injection when the engine is running and
the injector is between firing cycles.
Plunger (10) and the intensifier piston (8)
are at the top of the piston bore. The
cavity below the plunger is full of fuel.
In the upper end, the armature (3) and the
seated pin (4) are held down by the
armature spring (2) . High pressure
actuation oil flows into the injector. The
oil then flows around the seated pin to the
top of the check piston (16) . This
provides a positive downward force on the
nozzle check (19) at all times when fuel is
not being injected.
The spool valve (6) is held in the top of
the bore for the spool valve by the spool
spring (5) . In this position, the spool
valve blocks actuation oil from reaching
the intensifier piston. Actuation pressure is
felt on both the top and bottom of the
spool, so hydraulic forces on the spool are
balanced. The spool valve is held in the up
position or the closed position by the force
of the spool spring.