ReplyIf you google Tour and Andersson STA series balancing valves you should find CV/KV diagrams for your circuit setter (Sorry, I'm unable to post links yet). Then, measure the differential pressure across the valve and associate that and the number of turns with a flow in liters per second. The DN40 simply indicates the size (1-1/2"), and 150 is the pressure class. The PN20 I'm a bit confused by, unless the valve has flanged rather than soldered connections.
Post your results if you need any help converting between units. Also, remember to account for density when changing between l/s and gpm if you're using a glycol mixture in your loop.