If you do a set and your pump is getting more and more intense, then you should keep going and milk that for all it’s worth. If you think you’ve basically maxed out your pump, or you start to get a bit flatter, then go ahead and call it and move on to the next exercise.
The pump is NOT magic. It’s just a decent indicator of the intangibles that influence muscle growth.
Sets and reps really don’t matter all that much for your supplemental work!