The Medela Valves and Membranes pack support all Medela Breastpumps and kits. The Membranes revitalises and regulates suction for pumps, held together by the Medela Valves, without both the Breastpumps lose functionality.The Medela Valves and Membranes pack contains 2 spare valves and 6 membranes for use as a replacement part with Medela breastpumps and kits. With regular use of your Medela Breastpump, replacing the membranes and valves should occur every few months, or when you feel that the suction has reduced in power.