Yanmar 4LHA-HTP Operation Manual page 371

Chapter 3 Fuel Injection Equipment
5. Injection Pump Construction and Operation
Delivery Valve and Damping Valve
When the increased fuel oil pressure resulting
from the plunger's compression stroke has
overcome the delivery valve spring's set force
and the injection pipe's in-line residual pres-
sure, the delivery valve opens and fuel oil is
delivered to the nozzle holder and the nozzle.
(Fig. 16-A)
Then, when nozzle opening
reached, initial injection into the engine cylinder
occurs.
Fig. 16 Delivery valve operation
In the centre of the delivery valve is a piston.
After injection has ended and the piston edge
is contacting the top of the valve seat (Fig. 16-
B). the amount by which the injection pipe's in-
line pressure is reduced is proportional to the
volume of fuel retracted up to the time that the
delivery valve is completely closed.
pressure is
Delivery valve spring
.ri—IR,
Delivery valve
Delivery valve seat
This effective stroke is the plunger stroke from
the plunger's
sleeve's end-face during the delivery stroke, af-
ter the plunger barrel's inlet port and the plung-
er's inlet slit are closed.
It is proportional to the fuel injection quantity.
As can be seen in Fig. 15, control sleeve travel
to the left decreases the effective stroke, and
conversely control sleeve travel to the right in-
creases the effective stroke and the fuel injec-
tion quantity.
Although the beginning-of-injection position is
constant, end-of-injection varies according to
the control sleeve position. The control sleeve
position is determined by the governor.
When the plunger has lifted and injection has
ended, the pressure in the pressure chamber
suddenly decreases and the delivery valve
spring closes the delivery valve. In order to pre-
vent delayed injection it is necessary to main-
tain the residual pressure of the fuel oil in the
injection pipe for the next injection. The deliv-
ery valve functions to prevent reverse fuel oil
flow during the plunger's suction stroke.
Seating portion
Piston
J
jt:(piston diameter)
Because of this, cut-off of injection occurs im-
mediately after the end-of-injection and subse-
quent dripping is prevented. (Fig. 16-C)
3-1-14
i 4LHA Series i
cut-off port to the
- Retraction
. stroke
2
x retraction stroke
control