Figure 4. Fuel System Flow

Figure 3. Four Principle Plunger Positions of Injection Cycle

Figure 5. Helix and Charging Port Metering Positions

TM-5-3820-256-24-5 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
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SERVICE MANUAL GENERAL Section 1 Figure 4. Fuel System Flow FUEL SYSTEM FLOW As fuel travels through the fuel system, it will be under suction (negative pressure), intermediate pressure, high pressure (injection pressure) and low pressure (Figure 4). Negative Pressure The piston type supply pump creates a suction at its inlet and pulls fuel from the fuel tank, through the fuel supply lines and through the primary fuel filter. No filter is used on the fuel suction line extending into the fuel tank because wax particles could plug the filter in cold weather. Fuel lines and fittings between the supply pump inlet and the fuel tank must be a minimum of three-eighths inches inside diameter. Small diameter fuel supply lines or fittings will reduce fuel flow and can reduce engine power output. Intermediate Pressure The supply pump produces an intermediate pressure, called supply pump pressure, at its outlet and forces fuel through the final fuel filter and into the injection pump housing. Fuel under intermediate pressure surrounds each barrel assembly. Fuel pressure in the housing is controlled by the orificed fitting in the fuel return hose located "downstream" of the fuel return check valve and the supply pump piston spring calibration. A special rubber hose between the final filter outlet and the injection pump housing dampens pressure waves from the supply pump. Substitute hoses can cause lower engine power even though supply pump pressure can be within specifications. High Pressure The injection pump meters and delivers fuel at high pressure, up to an instantaneous 9000 psi pressure after nozzle valve opening, through the injection pipes or lines to the injection nozzle assemblies. This high pressure fuel causes the nozzle valve to open and fuel flows through the nozzle orifices into the combustion chamber. The amount of fuel delivered is controlled by the injection pump governor. A small amount of low pressure fuel returns from the nozzle assemblies to the fuel tank through the leakoff lines. Low Pressure An orifice fitting in the end of fuel hose from the fuel return check valve limits the amount of fuel returned to the fuel tanks. After fuel passes through the orifice, it is at low pressure. CGES-375 Printed in United States of America Page 3

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