Method of operating metal molding system configured to handle mold, system including injection unit having: output port; and machine nozzle defining conduit passageway, nozzle including: egress end, ingress end, conduit passageway for receiving molten metal; and mechanical valve received in passageway, valve positioned between egress end and ingress end, and valve operable in opened and closed positions. Method includes: processing volume of molten metal; placing valve in closed position, so that prior to application of injection pressure by unit, volume of molten metal is located; (i) downstream of valve, and (ii) between egress end and valve; and placing valve in opened position, so that volume of molten metal is injected, in response to application of injection pressure into, at least in part, mold cavity; and actuating valve to closed position, so that another volume of molten metal is located: (i) downstream of valve, and (ii) between egress end and valve.