Fuel injection nozzles

A fuel injection nozzle comprising a fuel pressure operable valve member slidable within a bore, a seating at one end of the bore, the valve member being shaped for co-operaton with said seating to prevent fuel flow from an inlet to an outlet, resilient means for biassing the valve member into contact with the seating, a chamber, a valve through which fuel under pressure can flow to said chamber, a surface in said chamber, the fuel pressure acting on said surface creating a force which assists the action of said resilient means characterized in that the valve is located in a first passage connecting said inlet with said chamber, said valve including a valve element and a valve seating, the valve element being lifted from the valve seating by the fuel pressure at the inlet to allow fuel flow into said chamber, a first piston subject at one end to the pressure in said chamber, a second piston of larger diameter than the first piston, one end of said second piston being engaged with the other end of said first piston, a second passage through which the other end of said second piston is subject to the pressure in said chamber, resilient means opposing movement of the pistons under the action of the pressure in the chamber acting on the differential area of the pistons, said pistons being positioned so that when they move against the action of the resilient means, the valve element of said valve will be held upon the valve seating to prevent a further increase in the pressure of fuel in the chamber.