That is correct, I have removed many competitive rubber bladders where someone put an external blue Brady check valve at the in water station base for some reason. I suspect because they saw them on airstones and soaker hose type membranes where the external is needed. The problem is when they aren't needed they are just another restriction. When they are needed they are not maintained as there is an o ring that only lasts 12-24 month (as a rule)I monitor my discs with the system pressure gauge and flex often never going over the max suggested cfm rate, My main pond has one display that has a large system in it with 5 stations, I have changed 3 station discs just to show and have the newest generation but still have 2 originals going from the 2002 installation.