When purging extruders that normally run with screen packs in place, be sure to discuss with your purging compound supplier whether the purging material will be able to pass through the screen mesh without hanging up.
And even if it will, don’t forget that part of a purging compound’s job is to break loose contaminants. If, for any reason, your screw and barrel is badly contaminated then even a purging compound that, by itself, would clear the screens with no trouble may break loose enough degraded material to clog the screens and rupture the screen pack.
If there probably is a significant amount of degraded material in the screw and barrel then the screens should come out.