The choke valve is the ball valve in the pusher line below the machine. In normal blasting it stays fully open — the handle aligned with the piping. Closing it while blasting drops the pusher-line pressure below vessel pressure, which forces abrasive down through the metering valve. That makes it useful for exactly two things:
Clearing minor blockages, such as damp abrasive: rapidly open and close the choke valve several times while blasting.
Rapidly emptying the machine of abrasive at the end of the day.
Don't blast choked. Never blast with the choke valve closed or partially closed — prolonged blasting that way accelerates wear on the abrasive metering valve.
