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1. The pump is basically a jerk type with a plunger moving in a matched barrel
2. Helical grooves machined in the plunger to control the end of injection by uncovering spill ports and causing the discharge pressure to drop rapidly, thus causing the needle valve in the injector to close.
3. Oil is supplied to the barrel via the spill ports and a suction valve.
4. The suction valve, situated at the top of the barrel opens during downward stroke of plunger, while spill ports are covered by plunger.
5. Replaceable erosion plugs are fitted in the pump housing opposite the spill ports.
6. The high pressure oil, spilling back, as the edge of the helix uncovers the spill ports at the end of injection, hit the plugs, which prevent damage to the pump casing
7. A puncture valve is fitted in the top cover of the pump. It is opened when compressed air from the control air system acts on top of a piston fitted in the top cover. Fuel oil from the discharge side is then returned to the suction side of the pump and no injection takes place.

 

How to check timing

Optical method

1. 1. 1. 1. 1. Set fuel rack to maximum
            2. Open spill plug of pump and clean thoroughly
            3. Turn engine 20 degree before TDC
            4. Ensure no oil, put light on suction 
            5. Wear goggle, look through spill port 
            6. Turn until TDC
            7. When light disappear, indicate start of injection

Oil overflow method 

1. 1. 1.  Stop fuel pump, 
      2. Fuel rack to max
      3. Take out delivery pipe, puncture suction valve,
      4. Turn to bdc, put DO, oil will flow out, 
      5. Turn towards tdc, flow will stop, record start of injection
      6. Continue until overflow again, indicate end of injection  

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