Case 1: 4" dia. x 100 US gpm x 155 F x 15 psig x oily water
Case 2: 18” dia. x 11,666 US gpm x 155 F x 259 psig x raw water
The straight pipe run upstream (ex. 5D) and downstream (ex. 2D) of check valves is required to make sure that there are no sudden cross-sectional changes (by tees, elbows, reducers, control valves, etc.) within these zones. However, I could not find any piping literature that prohibits the installation of branch connections such as vent, drain and instrument connections in the mentioned straight run. I suppose these branch connections are not significant contributing factors to turbulent flow due to their “no flow” conditions but I want to be sure.