Since North America is The Land of Baseball Caps - Well in my opinion anyway..

I thought Id ask a question concerning the cleaning of them..
I have a nice collection of Baseball Caps here at home and Ive got them hanging on the wall... Most of them are from the U.S.A. and Canada.
They are all very special to me and from use they have become dirty, salt stains from sweating and the list goes on..
Do you folks recommend washing them and what is the correct way if any?
Id like to do a major cleanup of them so they would look like new again.
But Im afraid to just whip them into the washer..


Can you assist?
Best wishes
Classic Finn