Construction. The Stanadyne pump, shown in …

1 Construction. The Stanadyne pump, shown in Figure 5-62 incorporates four pumping plungers. The driveshaft engages the distributor rotor in the hydraulic head. The rotor holds the four pumping plungers. The plungers are actuated simultaneously toward each other by an internal cam ring through rollers and shoes located in slots at the end of the rotor. The number of lobes normally equals the number of engine cylinders. Figure 5-62 - The Stanadyne DB4 injection pump uses four opposed plungers. The transfer pump is also a positive displacement vane type. It is enclosed in the end cap, which also houses the fuel inlet strainer and transfer pump pressure regulator. The distributor rotor incorporates two charging ports and a single axial bore. One discharge port serves all the outlet ports to the injection lines. The hydraulic head contains the bore in which the rotor revolves, the metering valve bore, the charging ports, and the head discharge fittings. The high pressure injection lines to the nozzles are fastened to these discharge fittings.

2 Stanadyne pumps have their own mechanical governor. The centrifugal force of the weights in their retainer is transmitted through a sleeve to the governor arm and to the metering valve. The metering valve can be closed to shut off fuel by an independently operated shut-off lever. The automatic speed advance is a hydraulic mechanism that advances or retards the beginning of fuel delivery. This can respond to speed alone or to a combination of speed and load changes. Components. The aluminum alloy pump housing of an opposed plunger distributor injection pump contains the driveshaft, distributor rotor, transfer pump blades, pumping NAVEDTRA 14050A 5-65 plungers, internal cam ring, hydraulic head, end plate, adjusting plates, transfer pump, pressure regulator assembly , governor, automatic advance, and metering valve. Driveshaft. The driveshaft connects to the engine drive gear and is supported by a bushing or ball bearing. It supports the governor assembly and drives the distributor rotor and transfer pump.

3 The transfer pump consists of four linear blades. It delivers fuel to the metering valve located in the hydraulic head at low pressure. It also provides a fuel inlet to the pump and contains a pressure regulating valve that controls the transfer pump pressure throughout the speed range. Hydraulic Head. The hydraulic head is machined with bores Figure 5-63 - Exploded view of a rotor assembly showing the cam rollers and shoes. and passages that allow fuel to flow from the transfer pump to the metering valve, from the metering valve to the charging ports, and from the discharging ports to the discharging fittings. On the latest designs, hydraulic heads have been fitted with individual delivery valves to maintain residual line pressure and eliminate secondary injection. Distributor Rotor. The distributor rotor is lapped fitted to the hydraulic head and the governor weight retainer assembly is fastened to its drive end. The plungers are fitted to the rotor and are pushed inward by the rollers and shoes to pump the diesel fuel.

4 The rollers fit into the shoes and contact the cam in a way similar to a cam follower, as shown in Figure 5-63. Adjusting plates are mounted on the rotor and limit the outward travel of the rollers and shoes to control the fuel delivery. Cam Ring and Metering Valve. A circular cam ring surrounds the rotor base and is located over the shoes and rollers. The number of internal cam lobes equals the number of cylinders. The cam ring forces the plungers toward each other, which causes the fuel to be pumped. It can also be rotated back and forth about the rotor to vary the start of injection. The metering valve contained in the hydraulic head regulates the volume of fuel entering the rotor. A piston valve is used with hydraulic governors. This valve is spring- loaded and controls the fuel according to the valve's axial position. When a mechanical governor is used, the valve is a rotary type, with a slot cut in the periphery. The valve is rotated by the governor arm to regulate fuel injection.

5 Automatic Advance and Governor. An automatic advance device is located I the bottom of the pump. A hydraulic piston rotates the cam ring against the direction of pump rotation via the cam advance stud. The cam advance stud threads into the cam and connects it to the cam advance mechanism. NAVEDTRA 14050A 5-66 The governor weight retainer may be permanently fixed, splined, or bolted to the rotor drive end. Because the fuel metering mechanism can be affected by vibrations and shocks, the retainer often uses a cushioning device to isolate engine vibration and pulsation from the driveshaft. One end of the governor control arm rests against the thrust sleeve, and the other end connects to the governor spring and to the metering valve via a linkage hook. The control lever is connected to the shut-off lever and the fulcrum lever is connected to the governor spring. Pump Operation and Fuel Flow. The operating principles of an opposed plunger pump can be understood more readily by following the fuel circuit during a complete pump cycle.

6 Figure 5-64 illustrates the fuel flow for a Stanadyne DB2 two-plunger distributor pump. The fuel flow for the DB4 four-plunger pump is the same with the exception of the charging of two additional plungers. As shown in the diagram, the transfer pump pulls fuel from the fuel tank. The fuel passes through a water separator and secondary fuel filter before reaching the transfer pump. Once through the transfer pump, some of the fuel is bypassed to the transfer pump's suction side through the pressure regulator assembly . Figure 5-64 - Fuel flow during the pumping cycle in a Stanadyne DB2 distributor injection pump. Fuel under pressure flows past the rotor retainers and into an annulus on the distributor pump rotor. Some fuel flows through a connecting passage in the head to the automatic advance mechanism. The remaining fuel moves into the charging passage. This fuel flows around the annulus, through a connecting passage, and to the metering valve. NAVEDTRA 14050A 5-67 The radial position of the metering valve regulates the fuel flow into the charging annulus, which holds the charging ports.

7 Pressure Regulating Valve Operation. The pressure regulating valve is located in the end plate and performs two important functions. When the injection pump is being primed, fuel is forced into the inlet connection through the mesh filter. Fuel enters the regulating sleeve located at the upper port, forcing the regulating piston downward and compressing the priming spring. When the piston has moved down far enough to uncover the lower port in the sleeve, the fuel flows directly into the hydraulic head. The pump is now primed and ready for start-up. When the engine is running, the pump rotates and fuel is pulled into the end plate by the transfer pump. It passes through the mesh filter and is forced into the hydraulic head and end plate. When the transfer pump builds pressure, it forces the piston upward against the regulating spring (Figure 5-65, View A). When the correct pressure is reached, the piston uncovers the regulating port. This bypasses a small amount of fuel back to the inlet side of the transfer pump to maintain fuel pressure at the desired level, (Figure 5-65, View B).

8 Transfer pump pressure can be adjusted in one of two ways. On some pumps, the spring guide is replaced with one of a different size. This changes the fuel pressure by altering the amount the regulating spring can be compressed. Other models are equipped with an adjustment device that can be set using a special tool when the pump is running on a test bench. Charging Cycle. As the rotor revolves, the two inlet passages align with the charging ports in the annulus. Fuel under pressure from the transfer pump and controlled by the metering valve flows into the pumping chamber, forcing the plungers apart. The plungers move outward a distance proportional to the amount of fuel required for injection on the following stroke. If a small quantity of fuel is admitted into the pumping chamber, the plungers move out a short distance. Maximum fuel delivery is limited by a leaf spring or springs that contact the edge of the roller shoes. During the charging phase of injection, the angled inlet passages in the rotor are in alignment with the ports in the charging annulus.

9 The rotor discharge port is not in alignment with a head outlet, as shown in Figure 5-66. The rollers are also off of the cam ring lobes. Figure 5-65 - Pressure regulating valve operation. NAVEDTRA 14050A 5-68 Discharging Cycle. As the rotor continues to revolve, as shown in Figure 5-67, the inlet passages move out of alignment with the charging ports. The rotor discharge port opens to one of the head outlets. The rollers then contact the cam lobes, and injection begins. Further rotation of the motor moves the rollers up the ramps, pushing the plungers inward. During this stroke, the fuel trapped between the plungers flows through the rotor's axial passage and discharge port to the injection line. Delivery to the injection line continues until the rollers move past the innermost point on the cam lobe and begin to move outward. The pressure in the axial passage is then reduced, allowing the nozzle to close and ending injection. Delivery Valve Operation. On some distributor pumps, individual delivery valves (sometimes called pressure valves) are installed in the hydraulic head outlets for each cylinder.

10 In other pump models, such as Stanadyne 's, a single delivery valve mounted in a bore in the center of the distributor rotor serves all injection lines. The delivery valve or valves keep the lines full of fuel so that a full charge of fuel can be injected at the next cycle for that cylinder. In addition, the delivery valve rapidly decreases injection line pressure to lower than nozzle closing pressure. This allows the nozzle to snap shut quickly without nozzle dripping or dribble that could cause excessive exhaust smoke. Figure 5-66 -Fuel flow during the opposed plunger pump's charging cycle. Figure 5-67 -Cutaway showing the opposed plunger pump's discharge cycle. Lubrication Circuit. The pump is located with diesel fuel supplied by the transfer pump. A lubrication groove runs from the annular ring to the front of the rotor. From this NAVEDTRA 14050A 5-69 point, the lubricating fuel flows to the main pump housing. At the top front of this housing, a return fitting allows fuel to return to the fuel tank, as shown in Figure 5-68.