Fuel pumps

Claim 1

A fuel pumping apparatus for supplying fuel to a compression ignition engine comprising a pumping plunger slidable within a bore, a cam for imparting inward movement to the plunger in timed relationship with the associated engine, means for distributing fuel displaced from the bore during successive inward movements of the plunger to a plurality of outlets in turn, said outlets in use being connected to the injection nozzles respectively of the associated engine, a spill valve operable to spill fuel from the bore during inward movement of the plunger, an actuating piston slidable within a cylinder, the actuating piston being biased by first resilient means towards an end wall of the cylinder, said spill valve comprising a valve member which is carried by the actuating piston and a seating which is formed in said end wall of the cylinder about a passage communicating with said bore, control valve means for admitting fluid under pressure into the cylinder to effect an initial movement of the actuating piston away from said end wall thereby lifting the valve member from the seating to allow fuel to spill from the bore into the cylinder and effect further movement of the actuating piston, a drilling formed in the actuating piston, the diameter of said drilling being slightly greater than the effective seat diameter of the valve member and seating, a balance piston slidable in said drilling, second resilient means biasing the balance piston in the direction towards said one end wall of the cylinder, a stop to limit the movement of the balance piston in the direction away from said end wall of the cylinder, and a passage in the valve member and actuating piston whereby the balance piston is subjected to the fuel pressure in the bore, said actuating piston and balance piston defining further valve means for connecting said bore to a source of fuel under pressure thereby to replenish the fuel lost through leakage and the fuel displaced through the outlet, said balance piston when the bore is full of fuel moving against the action of its spring loading relative to the actuator piston to interrupt communication between the bore and said source of fuel, the balance piston being moved into engagement with the stop during the initial inward movement of the plunger.