SERVICE MANUALNOZZLESSection 12FUNCTIONAL DESCRIPTION OF NOZZLEAND NOZZLE HOLDERNOZZLEThe UTDS* ADB-M type nozzles are of the closed,differential, hydraulically-operated type.Fuel, under high pressure, flows Into the fuel duct In thebody and enters the pressure chamber. When the fuelpressure in the pressure chamber exerts sufficient forceon the differential area of the nozzle valve to overcomethe opposing spring pre-load, the nozzle valve is lifted,allowing fuel to enter the nozzle body sac and flowthrough the spray holes. The fuel flowing through thespray holes is atomized as it enters the combustionchamber.When the end of the pumping stroke occurs, there is asudden drop in line pressure. As a result, the pressurein the nozzle pressure chamber drops rapidly. Since thepressure adjusting spring is exerting a downward forceon the nozzle valve and Is no longer being opposed byfuel pressure, the nozzle valve moves downward rapidlyuntil it seats in the nozzle body - the nozzle is nowclosed.Since there is a slight amount of clearance (controlled)between the nozzle valve and body, a small amount ofleakage between the valve and body will occur. Thisleakage is necessary for valve O D. and body l D.lubrication.NOZZLE HOLDERThe UTDS* AKN-M type nozzle holder is a unit whichretains the nozzle in the cylinder head and transfers thefuel from the high pr6ssure tubing to the nozzle duct.The holder assembly consists of a holder body, dowelednozzle spacer, lower spring seat, pressure adjustingspring, shims and a nozzle retaining nut.The holder body contains a high pressure tubingconnection at the upper end, a high, pressure fuel duct, aleak-off duct and drain connection. The lower end iscounterbored to accept the pressure adjusting spring andshims. The lower face is lapped to a fine surface finishand contains two locating dowel pin holes. The lowerspring seat provides a seat for the spring and a contactsurface for the nozzle valve stem. The nozzle spacercontains two locating dowel pins which locate the nozzleradially to the holder body to insure proper spray patternorientation. Both faces of the spacer are lapped to a finesurface finish to provide gasketless, high pressure sealsbetween the holder body face, spacer faces and nozzlebody face. The spacer also acts as the nozzle valvestop. The cap nut clamps the nozzle, and spacer, to theholder body.Fuel flowing through the high pressure tubing enters thenozzle holder and flows down the high pressure duct,through the spacer duct and to the nozzle. The slightfuel leakage between the nozzle valve and body entersthe spring chamber in the holder body and flows througha return duct to a drain connection.*United Technologies Diesel Systems(formerly AMBAC)CGES-185-3PRINTED IN UNITED STATES OF AMERICAPage 2
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