A pressurised fluid supply system (10; 10') for an agricultural vehicle, comprising: a. a main supply pump providing a first source of pressurised fluid to a steering system of the vehicle through a steering circuit and to other consumers through a main circuit; b. a cooling fan pump (14; 14') providing a source of pressurised fluid to a cooling fan motor (42; 42') driving a cooling fan through a cooling fan circuit; c. a prioritisation valve (480 for regulating the flow of fluid from the cooling fan pump (14; 14') to the cooling fan motor (42; 42'), the prioritisation valve having at least two operative configurations (48a, 48b) and movable between the two operative configurations in dependence on the fluid pressure in the steering circuit; wherein the cooling fan pump (14, 14') is fluidly connectable with the steering circuit so as to be able to provide a second a source of pressurised fluid to the steering system, the prioritisation valve being configured to adopt a first operative configuration in which fluid flow from the cooling fan pump (14; 14') to the cooling fan motor (42; 42') through the prioritisation valve is substantially unrestricted when the pressure in the steering circuit is at or above a first threshold value and to adopt a second operative configuration in which fluid flow from the cooling fan pump (14; 14') to the cooling fan motor (42; 42') through the prioritisation valve is partially restricted when the pressure in the steering circuit is below the first threshold value; characterized in that one of the cooling fan pump (14; 14') and the cooling fan motor (42; 42') is a variable displacement machine, the fluid supply system having a control system operative to adjust displacement of the variable displacement machine to maintain the input drive power provided by the cooling fan motor (42; 42') to the cooling fan substantially constant or at a demanded value and/or to vary the speed of the fan in accordance with cooling demand. a. a main supply pump providing a first source of pressurised fluid to a steering system of the vehicle through a steering circuit and to other consumers through a main circuit; b. a cooling fan pump (14; 14') providing a source of pressurised fluid to a cooling fan motor (42; 42') driving a cooling fan through a cooling fan circuit; c. a prioritisation valve (480 for regulating the flow of fluid from the cooling fan pump (14; 14') to the cooling fan motor (42; 42'), the prioritisation valve having at least two operative configurations (48a, 48b) and movable between the two operative configurations in dependence on the fluid pressure in the steering circuit; wherein the cooling fan pump (14, 14') is fluidly connectable with the steering circuit so as to be able to provide a second a source of pressurised fluid to the steering system, the prioritisation valve being configured to adopt a first operative configuration in which fluid flow from the cooling fan pump (14; 14') to the cooling fan motor (42; 42') through the prioritisation valve is substantially unrestricted when the pressure in the steering circuit is at or above a first threshold value and to adopt a second operative configuration in which fluid flow from the cooling fan pump (14; 14') to the cooling fan motor (42; 42') through the prioritisation valve is partially restricted when the pressure in the steering circuit is below the first threshold value; characterized in that one of the cooling fan pump (14; 14') and the cooling fan motor (42; 42') is a variable displacement machine, the fluid supply system having a control system operative to adjust displacement of the variable displacement machine to maintain the input drive power provided by the cooling fan motor (42; 42') to the cooling fan substantially constant or at a demanded value and/or to vary the speed of the fan in accordance with cooling demand.