I never remove my pump through security, I believe (and I travel quite a bit but don't necessarily quote me) you are fine to wear it through metal detectors but not through body scanners, so on the times when I have been asked to go in the scanner I have just said I have a pump and they have done a pat down and swabbed my hands instead. I used to carry a letter but I admit I haven't for years now but probably better to be safe than sorry, but I always carry insulin with the prescription label on.