when it reaches a level determined by the force exerted by the spring 30 the valve member is lifted from its seating to allow a restricted flow of fuel through the outlet or outlets 22 as the fuel pressure in the pump chamber increases the force exerted on the valve member by the fluid pressure eventually overcomes the action of both springs and the valve member moves to its fully open position as with the arrangement shown in fig1 the piston 27 will be urged by the pressure of the spilled fuel when the spill valve 11 is opened to exert a closing force upon the valve member to effect rapid movement of the valve member into engagement with the seating fig3 shows a modification to the arrangement shown in fig2 in as much as piston 27 is of a larger diameter and is engaged by both springs 30 and 31 this arrangement will operate in a similar fashion to the scheme shown in fig2 however in this case when the spill valve is opened the fuel under pressure entering the blind end of the spring chamber is now acts over a larger area of piston this will result in a greater force to assist in the closure of the valve member 21 the effective area over which the spilled fuel acts on the pistons in all arrangements can be chosen to adjust the closing forces acting on the valve member 21 to give closing characteristics optimised for performance and the life of the nozzle seating the arrangement shown in fig4 is substantially the same as that which is shown in fig2 except that the piston is not provided with the orifice 34 and the outlet.