Blastgates are designed to close off the airflow from one duct at a time, allowing the remaining duct system to get the benefit of the increased suction available.
Manual Blastgates are closed by hand, but rely on staff remembering to re-open the closed gate when the machines on that line are turned back on.
Pneumatic Blastgates are connected to the machine ON/OFF switch avoiding the error of leaving a Blastgate closed and a machine with no suction.