O.K.,
I've been researching this. I called March Pump. The March Pump Tech. said that he could not recommend a suitable material to use as a transition between the polysulphone (polysulphide) pump head and the stainless piping. He did say that the Guy that would know, wasn't in and asked that I call back later.
I worked in the chemical industry for many years. We routinely connected dissimilar materials. Even stainless and carbon steel to various plastics. We rarely needed anything to be food grade, so it normally wasn't an issue.
As most of us are aware, when dealing with high temperature, there is less danger of a "plastic" coupling failing than the chemical properties becoming unstable and "off gassing" into the product.
I spent quite abit of time with a Mcmaster-Carr Technical Rep. (Dave) trying to find a material that would handle 212F and still maintain its FDA rating. We looked at Polypropylene, Polyethylene, HDPE, LDPE, PTFE, Kinar, Nylon and sevaral others "blends" of Fluoroplastic fittings. The only thing that was close was schedule 80 CPVC. It is only good to 200F. The rest of the materials that started out FDA approved to begin with were only rated at 180F max. Kudos to Mcmaster-Carr's Tech. help section for all of their effort.
Then, I called March Pump back. I talked with Hans (apparently the Guy that knows), and he said that there was no problem hooking the pump directly up to the stainless piping. Just be sure that I didn't cross-thread, over tighten etc.. He said it would not void the warranty or otherwise violate the rules of international trade.
Sooo, I'm off to the shop to hook up my pump! Sorry for the long post, but I felt this was a very important piece of our hobby and wanted to get the straight info.
Now you know, and knowing is half the battle - G.I. Joe
Luck - Dwain