The purpose of the pumparound is to cool and partially condense the upflowing vapors.

By flash, it is assumed you mean the amount flashed in the flash zone after entering a column. If the amount flashed is more than you desire, lower the feed temperature. If the feed is some amount of saturated liquid and vapor, you will want to increase the percentage of liquid fed to the column. This applies to a general distillation column with more flash than desired.

If this is a crude oil atmospheric distillation column, and you are getting too much kerosene in a side draw, your cut point probably does not meet the required specification. In this case you will need to adjust your pumparound rates and/or increase the amount of reflux.