Abstract: A variable load valve for a vehicle braking system has a variable area ratio assembly the effective area ratio of which changes to tend to counteract unbalance of pressures between an input port and an output port and a double valve assembly which is moveable by a load dependent mechanism relative to the variable area ratio assembly, the double valve being arranged in the manner of a relay valve between the output port and a supply port or a vent port to relay pressure from the supply port to the output port in accordance with the magnitude pressure at the input port and the position setting of the double valve relative to the variable area ratio assembly. By provision of a further pressure responsive device a check valve and a further port the valve is adapted also to perform the function of a relay emergency valve.