The Medela Breastshield Valve and Membrane set comes with spare parts to keep your pump running smoothly. It's compatible with the Medela Pump in Style Advanced models and you can get two sets to have one on hand for each side. The breastshield with valve and membrane kit is easy to put together and to disassemble for cleaning. The set can be used with all Medela breast milk bottles. It's not compatible with Freestyle, Swing or Harmony breast pumps or PersonalFit breast shields. The Medela breast pump breast shield is an ideal replacement for a worn or damaged kit.