The invention relates to a method of fluid exchange using a separation apparatus, in controlled fluid communication with an inlet and an outlet. Opening of the inlet enables fluid communication with the separation apparatus, exchange of fluid (a “first fluid exchange”) of a first volume of fluid, sealing/closing preventing further fluid communication. Opening of the outlet to be in fluid communication with the separation apparatus enables exchange of fluid (a “second fluid exchange”) through the open outlet of a second volume of fluid. In the method, the outgoing volume of fluid and the incoming volume of fluid in each exchange are substantially similar and there is substantially no loss of pressure by virtue of the exchange. The invention also relates to a separation apparatus, including a separation chamber and a control system.