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Pippeta diaphragm that works to create the right suction for maximum comfort when expressing.. How often should the valve + diaphragms be changed?. Just like the valve, the diaphragms in the back-flow protectors can stretch and degrade over time, impacting suction. We recommend replacing these every 2 to 3 months if you pump once a day, and replace every 6 to 8 weeks if you pump more frequently.. Once opened this product may not be returned.