Multi-port flow control valves are provided wherein the outlet ports may be opened in cascade fashion to allow fluid to flow through the outlet ports into at least two conduits in which the opening of the outlet ports is controlled by a signal indicating the need for fluid in the conduits. The valves are particularly useful for controller the supply of heating/cooling fluid to multiple heating/cooling coils employed to control reactions. In a preferred embodiment the opening of the ports is controlled according to the heat measured in the reaction.