Why is it easy for a cryogenic valve to fail to move? How to solve it?
A: The cryogenic valve is installed at a normal temperature and operates at a low temperature, and the temperature varies widely. Thermal stress or deformation can easily occur if improperly designed or installed. At the same time, the operating part of the valve is at normal temperature and the circulating part is at low temperature. In order to reduce the cold loss, the stem is often made very long, it is easy to deform and get stuck.
Cryogenic valves tend to rotate flexibly at room temperature. They are tight at low temperatures and cannot even be opened. The main reasons for stuck valves at low temperatures are:
1. During installation, the valve and piping configuration is unreasonable and generates prestress; or the pipeline cold compensation capability is poor, and the valve position changes at low temperatures; or the valve lacks a bracket and deforms at a low temperature; or the valve is improperly fixed, and the cold box is deformed at a low temperature. It affects the concentricity of the valve stem and the valve body.
2. In terms of design, the linear expansion coefficient is different due to the different materials of the valve stem and the valve sleeve. General stem stainless steel, linear expansion coefficient of 1.73 × 10-6 °C -1; valve sleeve is brass, linear expansion coefficient of 19.9 × 10-6 °C - 1, that is, brass shrinkage is greater than stainless steel, may be low temperature Bite the thread. Especially when the dark rod structure and the fine thread are used, the temperature range of the thread buckle is large, the thread clearance is small, and biting phenomenon is more likely to occur.
3, in operation, due to the valve is not completely heated, or valve filling at the water, causing freezing at low temperatures, or close the valve at room temperature too tight, so that the screw bite bad.
In order to prevent the occurrence of valve jamming, it is advisable to adopt the structure of the bright rod and the trapezoidal thread of coarse teeth in the design; in the installation, there should be a firm bracket at the valve to prevent the valve stem from being bent when the valve generates displacement. The valve and the cold box can be fixedly connected by elasticity to prevent the valve stem from deforming and not concentric with the valve body. During the bare cold period, it is necessary to check and adjust the valve installation condition in the cold state, when it is found that the valve is stuck after cooling. The adjustable flange of the valve can be adjusted so that it can be opened and closed freely.
In operation, the warming before start-up should be complete, and the principle of airtightness should not be used when closing the valve. Do not use excessive force.
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