is shown the positioning device 38 comprising in part a first sealed cylinder 46 having an elongate member 48 passing therethrough and by way of an intermediate flange 50 provided thereabout dividing the cylinder 46 into a first compartment 52 and a second compartment 54 the member 48 is fixedly attached at a lower end 56 thereof to a point 57 on the suspension system of a rail vehicle 58 shown in fig3 and the cylinder 46 is attached thereto at another point 59 whereby when the vehicle is loaded and unloaded the member 48 moves relative to the cylinder 46 thereby altering the volume of the compartments 52 and 54 the positioning device 38 further comprises a second sealed cylinder 60 having an elongate hollow member 62 having an elongate hollow member 62 extending therethrough and by way of an intermediate flange 64 dividing the cylinder 60 into a first compartment 66 and a second compartment 68 a lower end 70 of the member 62 is fixedly and adjustably attached to the valve 12 an upper end 72 of the member 62 has provided thereabout a collar 74 to limit the travel of the member 62 through the cylinder 60 is supported on a bogey 76 of the rail vehicle 58 as is seen in fig3 and 4 a fluid line 78 is provided connecting compartments 52 and 68 whereas a fluid line 80 is provided connecting compartments 54 and 66 each line 78 and 80 has provided therein one or more bleed valves 82 in fig6 and 11 there is shown a valve 12 comprising an outer housing 84 and an inner cylinder bore 86 the bore 86 defines an area 88 of wide.