A continuous flow reactor, a method of performing a continuous flow reaction, and a method of controlling a moveable wall of a reaction chamber of a continuous flow reactor. The reactor comprising: an inlet; an outlet; and a reaction chamber, between the inlet and the outlet and providing a flow path therebetween, the reaction chamber having a moveable wall; the reactor further comprising: a pressure sensor configured to monitor a fluid pressure in the continuous flow reactor; and a controller, operable to adjust the position of the moveable wall, and thereby change a volume of the reaction chamber, based on the monitored fluid pressure.