Nozzles should be sized according to pipe sizing criteria, such as those provided in API RP 14E. The outlet nozzle is generally the same size as the inlet nozzle. To prevent baffle destruction due to impingement, the entering fluid velocity is to be limited as:
If an interior centrifugal (cyclone) separator is used, the inlet nozzle size should be the same size as the pipe. If the internal design requires the smallest inlet and exit pressure losses possible, the nozzle size should be increased.