It appears that you are properly using that .FRC to build your time history.
I wonder about your assigning a single .FRC file to two directions (elbow in and elbow out). I believe these .FRC files develop the leg imbalance as {[(P-upstream) - (P-downstream)] * (Inside Area)}. The leg is the straight run between two elbows, often termed the elbow-elbow pair on this Forum. It appears that you are assuming that the time history contains the pressure load on each elbow and that you must properly enter and orient these so that the imbalances are generated during the analysis.