Looks like you probably have enough info already but since I'm back in the office today and have it handy I'll send you this anyway. Here's a link to the one that we use. It's made by Deltec just for air compressor filters and we've had very good luck with them.
http://www.deltech-flair.com/support_files/pdf_files/SalesLit/ADVsalesLit.PDF#search='deltech%20automatic%20drain%20valve'
