One of our suppliers is having problems seal welding a valve body joint where the parts have been manganese phosphate coated. Base material is cast steel (WCB). Welds are not always so good, and don't seal.
I've read where welding over Mn-Phos is no big deal, and just the opposite. I'm...
If you have gate valves that have been working fine for 30 years, then you have the answer to your own question; buy more of those valves!
Otherwise stick with the names you know, the "players" in the industry. Check Thomas Register, for starters.
Depending on your location, you might want to contact a company in Aurora, Illinois named Ballco Manufacturing. I've had very good results using them as a valve ball supplier for many years.
ASME publishes a document called "BPE" (bioprocessing equipment) which may help you some, but it covers a lot of stuff besides valves. On the food processing side you may need to narrow your search a bit, since there are lots of groups and councils out there to deal with. In addition...
Joisy:
You might take a look at API STD 608, which covers ball valves and defines the dimensions required for full, regular, and reduced port valves.
The bad news is that not all ball valve manufacturers comply with API 608, so you may be left with checking catalog data anyway.