Powdered product was being dispensed into a bag when the powder stopped coming out of the fill spout. An employee reached up into the fill tube with his left hand/arm until his fingers reached the sliding gate valve, which opens/closes to start and stop the product flow. He pressed a button on a nearby solenoid valve with his right hand, opening the sliding gate valve in the fill tube. He then reached farther up in the fill tube and into the sliding gate valve. He released the button on the solenoid valve, which caused the sliding gate valve inside the fill tube to close and amputate his left-hand middle fingertip.