Metal bellows used for bellows valves are mainly hydraulic and welded. The hydraulic bellows increases the pressure resistance by increasing the number of layers, and the pressure resistance is good. Multi-wave one-shot molding or single-wave continuous molding, short production cycle, low price, high rigidity, small allowable displacement (single-wave displacement is 15% to 20% of the wave distance). The raw material is seamless pipe billet or seam pipe billet. The production process of extremely thin-walled seamless pipe is complicated. The welded pipe has high requirements on the welding equipment. The domestic small-diameter pipe production process is immature.
Hydraulic bellows has a high degree of standardization and serialization, and users can select models according to professional manufacturers’ samples. Welded bellows are generally single or double-layered, with limited pressure resistance. The number of welds is proportional to the wave number, the production cycle is long, the price is high, the stiffness is small, and the allowable displacement is large (the compression rate reaches 40% to 60%). The raw materials are plates or strips, which are relatively easy to obtain, and can be selected from materials with poor plasticity and good elastic properties, with poor standardization and serialization.
The operating conditions of bellows valves are becoming more and more severe, and higher requirements are placed on the materials of bellows. In the process of selecting the special material bellows for the valve, the appropriate material and the bellows forming method should be selected according to the specific conditions of the valve. The special material bellows for valves has the characteristics of high pressure resistance, high temperature resistance, corrosion resistance and long life. It will definitely become the development trend of valve bellows.
