Diesel Engine Troubleshooting

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Bosch Injection Pump Delivery Valves

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The main function of any delivery valve in the injection pump is twofold:

1. At the end of the plunger’s upward fuel delivery stroke, the delivery valve prevents a reverse flow of fuel from the injection line.

2. Figure 19-24 illustrates the sucking action that occurs at the delivery valve piston portion which controls the residual pressure in the injection line so as to effectively improve the injected spray pattern of the fuel without fuel dribble and possible secondary injection. The sucking action that does occur at the delivery valve therefore effectively reduces the fuel pressure in the injection tube at the end of injection.

Bosch Injection Pump Delivery Valves Bosch Injection Pump Delivery Valves

The delivery valve, or what is sometimes referred to as a discharge valve, is specially designed to assist in providing
a clean, positive end to injection. Below the valve face is a collar that is a precision fit in the valve bore. When pressure is created in the pump above the plunger by the closing of the ports, the valve must be raised far enough off its seat for the collar to clear the bore.

At the end of injection when pressure in the pump chamber is relieved by the opening of the control port, the valve drops down on its seat assisted by spring pressure. A volume of fuel equal to the displacement volume of the valve is added to the line and nozzle, reducing this pressure and allowing the nozzle valve to snap shut without the cushioning effect of pressure retained in the line and nozzle, such as with the closing of an ordinary valve. This is commonly called line retraction, which lessens the possibility of secondary injection or after-dribble at the spray nozzle. It is accomplished by an antidribble collar (accurately fitted relief or displacement piston) located at the upper end of the valve stem just below the seat.

Written by Ed

September 3rd, 2011 at 6:18 am

Posted in Bosch Fuel Systems

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Diesel Engine Delivery Valves Service

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Delivery-valve problems are cylinder specific. If the valve sticks open, no fuel passes to the associated injector. Leakage is harder to diagnose. White smoke that persists after all bases have been touched—pump pressure and timing, new injectors, and engine compression—suggests that one or more delivery valves may be at fault. Disassemble one valve at a time, clean the parts thoroughly, and test for leaks by blowing through the outlet port. Older, simpler valves can sometimes be resurfaced. Check piston fit by depressing the valve and placing your finger over the inlet port (Fig. 5-20). You should feel the vacuum as the piston falls.

fuel delivery valve test Diesel Engine Delivery Valves Service

Written by Ed

February 11th, 2011 at 1:53 am

Posted in Fuel Systems

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Diesel Engine Delivery Valves

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Injectors feed through delivery valves mounted on the distributor head or above each barrel on inline pumps. These check valves open under pressure to supply fuel to the injectors and close automatically during the suction stroke. Most delivery valves consist of a conical sealing element shaped like an inverted top hat (Fig. 5-19). The extension below the element, known as the piston, has two functions. It centers the valve over its seat and acts as a ram to force fuel back into the pump as the valve closes. This action assures a rapid drop in pressure so that the injector snaps shut without after-dribble.

Delivery valves come in various shapes and sizes. Some replace the conical element with a disc, others hold a certain percentage of pressure in the downstream plumbing after closing. But all work on the same general principle.

fuel delivery valve Diesel Engine Delivery Valves

Written by Ed

February 11th, 2011 at 1:51 am

Posted in Fuel Systems

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