What are the selection and application of metal bellows for valves? - 1

Release time:

2024-03-15

Answer: introduce the application, design and selection of metal bellows in stop valve, gate valve, regulating valve, safety valve and ball valve. The solution to the problems in the use of metal bellows for valves is given.

(1) with the enhancement of environmental protection awareness in the world, people have higher and higher requirements for valve sealing, especially in the special occasions such as this device and petroleum and chemical industry, which requires that the valve must achieve "zero leakage". Therefore, the Soviet Union, Germany, the United States, Japan and other countries took the lead in the application of metal bellows in the field of valves. As a new product, bellows valve was first applied in the fields of aviation, aerospace, shipbuilding, nuclear industry and other military industries, and rapidly promoted in the fields of petroleum and chemical industry.

The function of metal bellows is to measure, connect, transform, compensate, isolate, seal and reduce vibration. In the bellows stop valve and gate valve, the main functions are isolation, sealing and compensation. In the self operated regulating valve, it also plays the role of output force and opening and closing the valve in combination with the spring.

There are two main types of metal bellows used for bellows valve: hydraulic forming and welding forming. According to the actual valve body height, displacement, pressure resistance capacity and rigidity requirements, which type of metal bellows should be selected should be considered comprehensively. The materials of metal bellows are mainly austenitic stainless steel and high-temperature alloy steel, etc. the selection of materials is mainly determined by the corrosiveness of the actual service medium and the service temperature of the valve.

Due to the rapid development of domestic valve industry in recent years, how to select the appropriate metal bellows in the design of bellows valve has become an urgent problem to be solved in the industry.

(2) in terms of the design and selection of metal bellows, the industry terms of metal bellows shall be defined first.

1) bellows: an elastic, thin-walled tube shell part with multiple transverse corrugations.

2) bellows assembly: it is composed of two or more parts, one of which is bellows, the bellows is one or more in series, the other is flange and other accessories.

3) wall thickness: the wall thickness of the original metal pipe forming the bellows, and for the multi-layer bellows, the total wall thickness of each layer.

4) stroke: Based on the original length, the sum of compression displacement and tensile displacement of bellows.

5) distortion; column instability caused by axial compression of long corrugated tube.

6) nominal pressure: design pressure related to mechanical strength of bellows.

7) nominal load: the maximum load or full range value allowed under normal working conditions. Generally, the expected design value overload load is generally limited to 125% ~ 150% of the rated load.

8) rated displacement: the displacement under rated load is the allowable working displacement under normal use conditions. The allowable displacement without plastic deformation is generally 40% ~ 50% of the allowable displacement.