A fire suppression system for an aircraft having a plurality of enclosures, the fire suppression system comprising a plurality of directional valves, each provided in an agent discharge line to an enclosure for controlling the discharge of fire suppression agent to that enclosure, and each comprising a valve member for controlling the discharge of fire suppression agent, wherein the valve member comprises: a blocking portion to provide a closed setting for the fire suppression agent; a first orifice to provide a fully open setting for the fire suppression agent; and a second orifice to provide a restricted opening setting in which flow of fire suppression agent is restricted, wherein the valve member is configured so that during opening of the directional valve from a closed setting, the first orifice follows the blocking portion and precedes the second orifice in order to provide a fully open setting followed by a restricted opening setting, wherein the system further comprises a control unit that is configured so that if a first fire in a first enclosure is detected, it regulates the pressure of the fire suppression agent reaching the directional valves so that a high rate discharge of fire suppression agent is provided to the first enclosure initially, followed by a low rate discharge of fire suppression agent once sensors (8b, 11, 18) indicate that the fire is extinguished or sufficiently subdued, wherein the second orifice or each directional valve is sized to produce a level of discharge of fire suppression agent when subjected to a high-rate-discharge pressure that corresponds to a low rate discharge using the first orifice under a low-rate-discharge pressure, in that the control unit is arranged to send a warning signal (32, 34) to the cockpit, wherein a manual control is provided in the cockpit to open the directional valve, and in that the control unit is configured so that if a second fire is detected in a second enclosure and the first enclosure is being subjected to a low rate discharge of fire suppression agent, then the control unit: permits further actuation of the directional valve for the first enclosure to select the second orifice; and regulates the pressure of the fire suppression agent reaching the directional valves of the first and second enclosures to a higher-rate-discharge pressure in order to produce a high rate discharge of fire suppression agent in the second enclosure while the discharge rate in the first enclosure is restricted by the second orifice of the directional valve for the first enclosure. a blocking portion to provide a closed setting for the fire suppression agent; a first orifice to provide a fully open setting for the fire suppression agent; and a second orifice to provide a restricted opening setting in which flow of fire suppression agent is restricted, wherein the valve member is configured so that during opening of the directional valve from a closed setting, the first orifice follows the blocking portion and precedes the second orifice in order to provide a fully open setting followed by a restricted opening setting, wherein the system further comprises a control unit that is configured so that if a first fire in a first enclosure is detected, it regulates the pressure of the fire suppression agent reaching the directional valves so that a high rate discharge of fire suppression agent is provided to the first enclosure initially, followed by a low rate discharge of fire suppression agent once sensors (8b, 11, 18) indicate that the fire is extinguished or sufficiently subdued, wherein the second orifice or each directional valve is sized to produce a level of discharge of fire suppression agent when subjected to a high-rate-discharge pressure that corresponds to a low rate discharge using the first orifice under a low-rate-discharge pressure, in that the control unit is arranged to send a warning signal (32, 34) to the cockpit, wherein a manual control is provided in the cockpit to open the directional valve, and in that the control unit is configured so that if a second fire is detected in a second enclosure and the first enclosure is being subjected to a low rate discharge of fire suppression agent, then the control unit: permits further actuation of the directional valve for the first enclosure to select the second orifice; and regulates the pressure of the fire suppression agent reaching the directional valves of the first and second enclosures to a higher-rate-discharge pressure in order to produce a high rate discharge of fire suppression agent in the second enclosure while the discharge rate in the first enclosure is restricted by the second orifice of the directional valve for the first enclosure. permits further actuation of the directional valve for the first enclosure to select the second orifice; and regulates the pressure of the fire suppression agent reaching the directional valves of the first and second enclosures to a higher-rate-discharge pressure in order to produce a high rate discharge of fire suppression agent in the second enclosure while the discharge rate in the first enclosure is restricted by the second orifice of the directional valve for the first enclosure.