I'm glad to know they have malfunctioned for others. Had thought it was just me. : ). Thanks for the tip. Mine didn't stay stuck though. I had to take pics while exhaling on old and new to figure out that the new one was opening during exhale, preventing new flutter valve from working, then it quickly closed again. It didn't happen on all of them-just part at that time. I tried an Accapella and it worked great until just after Amazon return period ended : ), then the small plastic piece holding flutter valve broke. I rarely bring up sputum and mostly gave up then. I use exercise or Autogenic drainage app now. Note-I do have a working and clean Aerobika to use if I start producing mucus. So many here like it, it must help with that.