For systems equipped with capacity control compressors, or where tandem or multiple compressors are used with one or more compressors cycled off for capacity control, a single suction line riser may result in either unacceptably high or low gas velocities.
A line properly sized for light load conditions may have too high a pressure drop at maximum load, and if the line is sized based on full-load conditions, velocities may not be adequate at light load conditions to move oil through the tubing.