These replacement valves and membranes are designed for compatibility with Medela breast pumps that use Medela-style valves and membranes such as the Medela Symphony and Harmony. The membranes are engineered by MayMom to be more flexible than Medela original part, allowing them to respond more quickly to pressure changes during pumping for reliable performance. The specially angled valves help reduce milk retention, minimizing the amount of precious breast milk trapped inside the valve. Each set includes a convenient storage case that protects components and makes organization and travel easier. This value pack includes 4 valves and 6 membranes, providing dependable replacements to keep your pump operating at its best.