SERVICE MANUAL
NOZZLES
Section 12
FUNCTIONAL DESCRIPTION OF NOZZLE
AND NOZZLE HOLDER
NOZZLE
The UTDS* ADB-M type nozzles are of the closed,
differential, hydraulically-operated type.
Fuel, under high pressure, flows Into the fuel duct In the
body and enters the pressure chamber. When the fuel
pressure in the pressure chamber exerts sufficient force
on the differential area of the nozzle valve to overcome
the opposing spring pre-load, the nozzle valve is lifted,
allowing fuel to enter the nozzle body sac and flow
through the spray holes. The fuel flowing through the
spray holes is atomized as it enters the combustion
chamber.
When the end of the pumping stroke occurs, there is a
sudden drop in line pressure. As a result, the pressure
in the nozzle pressure chamber drops rapidly. Since the
pressure adjusting spring is exerting a downward force
on the nozzle valve and Is no longer being opposed by
fuel pressure, the nozzle valve moves downward rapidly
until it seats in the nozzle body - the nozzle is now
closed.
Since there is a slight amount of clearance (controlled)
between the nozzle valve and body, a small amount of
leakage between the valve and body will occur. This
leakage is necessary for valve O D. and body l D.
lubrication.
NOZZLE HOLDER
The UTDS* AKN-M type nozzle holder is a unit which
retains the nozzle in the cylinder head and transfers the
fuel from the high pr6ssure tubing to the nozzle duct.
The holder assembly consists of a holder body, doweled
nozzle spacer, lower spring seat, pressure adjusting
spring, shims and a nozzle retaining nut.
The holder body contains a high pressure tubing
connection at the upper end, a high, pressure fuel duct, a
leak-off duct and drain connection. The lower end is
counterbored to accept the pressure adjusting spring and
shims. The lower face is lapped to a fine surface finish
and contains two locating dowel pin holes. The lower
spring seat provides a seat for the spring and a contact
surface for the nozzle valve stem. The nozzle spacer
contains two locating dowel pins which locate the nozzle
radially to the holder body to insure proper spray pattern
orientation. Both faces of the spacer are lapped to a fine
surface finish to provide gasketless, high pressure seals
between the holder body face, spacer faces and nozzle
body face. The spacer also acts as the nozzle valve
stop. The cap nut clamps the nozzle, and spacer, to the
holder body.
Fuel flowing through the high pressure tubing enters the
nozzle holder and flows down the high pressure duct,
through the spacer duct and to the nozzle. The slight
fuel leakage between the nozzle valve and body enters
the spring chamber in the holder body and flows through
a return duct to a drain connection.
*United Technologies Diesel Systems
(formerly AMBAC)
CGES-185-3
PRINTED IN UNITED STATES OF AMERICA
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