... the rotation of open and close the valve stem, but use and driver withcircular disc (valve ... type gate valvesracteristics: the gate valves are handwheels, stem and packing in central, threaded, small culvert ... , especially the part to corrosion, threads from stem revealed the bonnet highly judge, in order to ... resistance to flow, open effort and closed stem and packing culvert of contact with the media ...