In a hydraulic system (10) for a tractor, a main pump (12) supplies fluid to a steering system (22) through a steering circuit (24) and a second pump (14) supplies fluid to a cooling fan motor (42). The second pump is connected with the steering circuit to provide a second a source of fluid to the steering system when the main pump is unable to meet demand. A prioritisation valve (48) regulates the flow of fluid from the second pump to the motor. The valve has a first operative configuration (48a) in which fluid flow from the second pump to the motor is unrestricted and a second operative configuration (48b) in which fluid flow from the second pump to the motor is blocked or restricted. The valve adopts the second operative configuration when the pressure in the steering circuit is below a first threshold value. The second pump acts as a secondary pump for the steering system and drives a cooling fan.