Valve Operating Torque
When the valve opening in the 10% when the axial force of the valve, valve operating torque was little changed. When the valve opening is less than 10%, due to the fluid stream, gate valves before and after the differential pressure increases. The differential pressure on the gate, the stems need to be axial force to drive the gate of great, so in that context, gate valves operating torque is great. Flexible gate valve, close off the required operating torque greater than rigid gate.
When the gate is closed, due to the sealing surface of the seals in different ways, will have a different situation. Self-sealing gate valves (including flat gate valve), when the valve is closed, the gate sealing surface of valve seat sealing surface, which is a gate valve to full open position. Valve operating conditions at this location cannot be monitored, in practical use, is the position of the valve close to check point as the gate fully closed position. Thus, automatically sealed gate valve closed position is according to the gate position (stroke) to determine. Mandatory seal gate valve, closed gate must be exerting pressure on the seat. This pressure to ensure the gate seal and valve seat sealing surface strictly, is the forced seal gate valve sealing force. The sealing force due to the stem nut, self-locking, will continue to do. Obviously, in order to provide gate sealing force, passing moment than the valve stem nut torque during its operation. Thus, mandatory sealing valve, full off position according to the torque on the valve stem nut to determine the size.
When the gate is closed, due to the change in medium or ambient temperature, thermal expansion valve parts brake plate between the seat and the pressure becomes larger, reflecting on the stem nut, then open valve more difficult. So, opened gate by needed of torque than close gate by needed of torque big, also, for pair each other contact of sealed surface for, they Zhijian of static friction coefficient also than moving friction coefficient big, to makes they from still State produced relative movement, needed imposed larger of force to overcome static friction; due to temperature changes, makes sealed surface between of pressure variable big, need overcome of static friction also with of variable big, to makes opened gate Shi, on valve Rod nut Shang imposed of torque sometimes will increases many.