After cleaning out melamine resin lines that were blocked, an employee wanted to verify that a control valve was operating properly. While standing on a 4-foot ladder, the employee reached over to the far side of the valve and manually actuated the solenoid, causing the valve to open. The employee's right middle finger was in the valve to verify it was open when the employee lost their footing and released the solenoid. The valve then closed and amputated the right middle fingertip.