Thanks for the responses
Wrong symbols were used on the drawings! They are not stopples. I found out they are check valves not stopples but called out that way.
There are many types of check valves- wafer checks, swing checks, plate checks, lift checks, piston checks, nozzle checks, etc. Which one are you after?
If you are working with the classic K value method, then K = 2.0, while L/D = 135 for a swing check. Pls note that the Fanning friction factor to be used for this classic approach for fittings pressure drop must always range between 0.016 to 0.02, regardless of what the computed flow regime friction factor is.
If are using the 3-K method, then K = (2025/Nre) + 0.621 [1 + 4.0 (25.4/ID)^0.3], where ID = pipe id in mm, Nre = piping Reynolds number. I've had to extrapolate this myself from other known info, since there is no literature for swing checks in the 3-K docs.
Pls also note there is a minimum velocity which must be exceeded for swing / dual plate checks to enable stable flow - you may glean this off the internet - but be careful to cross check this against other guidance.