Cryogenic pneumatic valve why easily jammed pull still occur?

why cryogenic pneumatic valves easily jammed pull still occur?
pneumatic valve is installed at room temperature at low temperature, low temperature, the temperature change range is very large. If the improper design, installation, it is easy to produce thermal stress and deformation. At the same time, the operation of the pneumatic valve parts at room temperature, circulation part in low temperature. In order to reduce the cold damage, pneumatic valve stem often do very long, also is easy to produce deformation and stuck. Pneumatic valve is flexible rotation at room temperature at low temperature, low temperature is very tight, even can't open it.

the main reason for the pneumatic valve is stuck in the low temperature?
, when installation, pneumatic valves and piping configuration is not reasonable and prestressed; Or pipe cold compensation ability is poor, low temperature air valve position change; The lack of support or pneumatic valve, in the low temperature deformation; Improper or pneumatic valve fixed, protect cold box under the low temperature deformation and affect the concentricity pneumatic valve stem and valve body.
, in design, as a result of pneumatic valve stem and valve sleeve material is different, different linear expansion coefficient. General pneumatic valve stem with stainless steel, the linear expansion coefficient is. ×- ℃, ； Pneumatic valve set for brass, linear expansion coefficient is. ×- ℃, , that is, the shrinkage of brass is larger than the stainless steel, low temperature could thread is biting. Especially when using non-rising stem structure and fine thread, thread wide temperature range, thread clearance is small, more prone to biting.
, in operation, the pneumatic valves in heating is not complete, or pneumatic valve packing place into the water, under the low temperature caused freezes, or at room temperature to the pneumatic valve closed tight, the thread is chewed, etc.

the pneumatic valve is stuck in the low temperature how to solve?
in order to prevent occurrence of pneumatic valve sticking phenomenon, appropriate USES stem structure on the design and coarse thread trapezoidal thread; On the installation should be had strong support in the pneumatic valve, pneumatic valve with pipe to prevent displacement and the pneumatic valve rod bent. Pneumatic valve and fixed can adopt flexible connection of cold box, prevent deformation of the pneumatic valve rod and differ with pneumatic valve heart; During the naked cooling, be under cold condition check and adjust the pneumatic valve installation, when when he found the phenomenon of the pneumatic valve cooling after stuck, pneumatic valve can be adjusted in the fixed on the shell flange, switch freely.
in the operation, right before the start of the heating should be complete, close the pneumatic valve to the principle of not leak when don't too hard.