Back pressure serves two important roles… 1) to help ensure proper material mixing. 2) to help ensure a homogeneous melt compression in front of the screw. Your back pressure should be high enough to provide both of these.

The first factor is easily determined by part quality and inspection.

The second factor is determined by the consistency of your recovery time.

Keep in mind, you may not receive a consistent melt recovery until you first optimize your rear temperature zone.

-Andy