Large diameter valve
Classification:
Release Time：2018-09-11
1. Analysis of the reasons for the difficulty in opening and closing large-diameter valves: Generally, the flow direction of the stop valve is designed to be low and high. When people close the valve, the human body pushes the handwheel horizontally to rotate to make the valve flap move downward to realize closing. At this time, it is necessary to overcome the combination of three forces: 1) axial thrust; 2) Friction between packing and valve stem; 3) The larger the diameter of contact friction between the valve stem and valve disc core, the axial thrust is also larger, and when it is close to the closed state, the axial thrust is almost close to the actual pressure of the pipe network. 2. Analysis of the causes of internal leakage of large-diameter stop valves. Large-diameter stop valves are generally used in boiler outlets, main sub-cylinders, steam main pipe and other positions.
1, large diameter valve switch difficult reason analysis:
The flow direction of the general stop valve is designed to be low and high. When people close the valve, the human body pushes the hand wheel to rotate horizontally to make the valve flap move downward to achieve closure. At this time, the combination of three forces needs to be overcome:
1) Axial jacking force;
2) friction force between packing and valve stem;
3) contact friction between valve stem and valve disc core
The larger the diameter, the greater the axial thrust, when close to the closed state, the axial thrust is almost close to the actual pressure of the pipe network.
2. Cause analysis of internal leakage of large diameter stop valve
Large diameter cut-off valve is generally used in the boiler outlet, the main cylinder, steam pipe and other positions, these positions have the following problems:
1) the boiler outlet pressure difference is relatively large, so the steam flow rate is also greater, the sealing surface erosion damage effect is also greater. In addition, the boiler combustion efficiency cannot be100%This will cause the steam at the boiler outlet to have a large water content, which is easy to cause cavitation and cavitation damage to the valve sealing surface.
2) For the stop valve near the boiler outlet and the sub-cylinder, because the steam just coming out of the boiler has intermittent overheating, in the process of saturation, if the boiler water softening treatment is not very good, some acid and alkali substances will often precipitate, which will cause corrosion and erosion to the sealing surface. There are also some crystallizable substances that may adhere to the valve sealing surface and crystallize, resulting in the valve not being sealed tightly.
3) Sub-cylinder inlet and outlet valves, due to the amount of steam behind the valve, production requirements and other reasons, the amount of steam used is large and sometimes small, in the case of large changes in flow rate, it is easy to produce flash, cavitation and other phenomena, thus causing erosion, cavitation and other destructive effects on the valve sealing surface.
4) Generally, when a large-diameter pipeline is opened, the pipeline needs to be preheated, and the preheating process generally requires a small flow of steam to pass through, so that the pipeline can be heated slowly and evenly to a certain extent before the stop valve can be fully opened to avoid excessive expansion caused by rapid heating of the pipeline and damage to some connecting parts. But in this process, the valve opening is often very small, resulting in erosion rate is far greater than the normal use effect, seriously reduce the service life of the valve sealing surface.
3, large diameter stop valve switch difficult solution
1) First of all, it is recommended to choose the bellows seal stop valve to avoid the friction resistance of the plunger valve and the packing valve, and the switch is easier.
2) the valve seat must choose erosion resistance, good wear performance of the material;
3) It is recommended to adopt a double disc structure, which will not cause excessive erosion due to small opening, which will affect the service life and sealing effect.
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2026/02/28
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