We bought our new (used) pasteurizer last fall, never thinking that it didn’t come with a manual. After weeks of internet searches, emails, and phone calls, we finally found someone who knows how it works.
It turns out the hot water (yes, thankfully it’s designed for hot water, not steam) is delivered under pressure, sprays against the inner liner to heat the milk, and collects at atmospheric pressure in a reservoir at the bottom. That means we need a second pump to cycle the used water back into the heater, else it exits through the overflow. Who knew?