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The operation of Timing Valve In Common Rail Systems

Posted on 2/16/2016 2:39:26 PM

The fuel pump,called "jerk type" pumps,  can pump the fuel to the injectors, the start and termination of fuel injection as well as meter the correct amount of fuel to the fuel injectors, with respect to the engine load. The start and stop of fuel injection is decided by "timing valves",instead of the fuel pump which fuel oil at a very high pressure into the common rail,with emphasis on the "Doxford" engines.
Meanwhile it is also usually a reciprocating pump driven by the main engine.The "timing valves" could be found in the front of each unit.

Referring to the figure beside, the timing valve and its cam are seen with the "common rail" high pressure line, on the discharge side of the reciprocating fuel pump. 

There is a separate accumulator bottle provided on the high pressure common rail line in order to avoid the pressure fluctuations or shock due to the change in load on the main engine. Then the high pressure fuel oil awaits for the opening of the timing valve (arrangement includes cam, lever, and valve block). When the cam peak lifts the lever up, the lever in turn opens the valve on the valve block, thus allowing the high pressure oil to reach the fuel injectors mounted on the cylinders of each unit. As the engine crankshaft rotates, thus making the cam to rotate causing the peak to move, the lever returns back from its lifted position, thus allowing the valve on the valve block to close,stopping further fuel oil flow to the fuel injectors.

The fuel injection period is decided by the duration of the opening of the valve in the valve block which can be altered by adjusting the fulcrum point on the valve lifting lever "L." At no delivery, the fulcrum remains at its lowest position. During this stage, the cam peak just oscillates the lever, but the valve is not opened in the valve block, thus no fuel is being injected.

Correct amount of fuel could be metered to each unit by the fuel pumps.Based on the engine load, the governor controls the fuel rack of the fuel pump as seen in the adjacent figure.Then the fuel pump deliver the regulated quantity of fuel to the timing valve.These fuel pumps have a helical slot in the plunger, the same as in conventional pumps. This ensures that the correct quantity of fuel is always injected with respective variation in engine load.

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