I am agree with you diaphragm pumps are really useful to use..You can use it how ever you are want to do with it.You can use them how ever you are want to use them by the opening and closing the valves...diaphragm pumps are much quieter than piston pumps, but do not last as long nor deliver the same PSI consistently when there is significant back pressure
but they are quiet and you can replace the diaphragm when they wear out.