Employees were unloading material from a barge to a storage tank. A logistics employee was lowering the unloading arm at the barge dock. The employee provided the barge operator the rope used to guide the unloading arm from the dock down to the barge. The logistics employee pulled both pins that secure the counter weight when not in use. The logistics employee then grabbed the back of the counter weight handle and pulled the counter weight toward themself. As the logistics employee was guiding the counter weight past the unloading valve handle, the counter weight pushed back too far and struck the unloading valve handle. The operator's pinky finger was caught between the unloading valve and counterweight, resulting in a partial amputation.