I can't add much, but my Dad catered to the self service car washes in northern CA. The ones you drop your quarters in and grab the wand. The pumps he favored were CAT, and Giant. Probably because they were easy to get parts for. I know that he would occasionally rebuild one, but it wasn't a big part of his business. I wished I had worked with him more knew how to put one together. I know there was a regulator to add soap, but I don't remember if there was any overload protection.
Larry
