The valve stem is used to open and close the closing parts and transmit the sealing force. The opening and closing actions of the valve are realized by the power device, the valve stem and the valve stem nut.In addition to bearing the axial force, the valve stem also bears the torque of the transmission mechanism, and its force is more complicated.
  The valve stem is a shaft-like part whose length is greater than its diameter.It is generally composed of an outer cylindrical surface, an outer thread, an outer conical surface and the outer four sides.According to the different end structure, the valve stem can be divided into two types with sealing cone and without sealing cone.Although the structure of the valve stem is different, it also has its common characteristics.
1. High degree requirements
  The valve stem has an outer cylindrical surface with high roughness requirements.The outer cylindrical surface of the valve stem is in close contact with the packing. In order to prevent the valve stem from scratching the packing during rotation or axial movement, and to ensure the seal between it and the packing, the roughness of the outer cylindrical surface is required to be high, generally Ra3.2. 0.8~XNUMXum.
2. With external thread
  Except for the stems of individual valves such as ball valves, most stems have external threads.The external thread is used to convert the rotational movement of the power device or transmission device into the axial movement of the valve stem to realize the opening and closing of the valve.In order to be able to withstand larger axial loads, the valve stem usually uses a single-head standard trapezoidal thread.
The main technical parameters of the valve stem
The main technical requirements of the valve stem include surface accuracy and tolerance.
1. Surface accuracy
  阀杆外圆的直径精度一般为11级，表面粗糙度为Ra3.2~0.8um。螺纹精度为7~9级，表面精糙度为Ra6.3~3.2um.。密封锥面的表面粗糙度为Ra3.2~0.4um。
2. Tolerance
  阀杆的轴心线直线在全长上不应超过外圆直径公差的1/2。外圆柱的锥度在每100mm长度上不得大于0.015mm。螺纹、密封锥面对外圆柱的同轴度一般不超过外圆柱直径公差的1/2。