What is a bellows valve?

Bellows structure
The bellows tube is welded to the valve cover and valve stem. The bellows tube has many crimps, which are compressed or expanded according to the movement of the valve stem. (Scientifically speaking, when the valve is in the open position, the bellows will be compressed, when the valve is in the closed state, the bellows will expand). It is important to install the valve body correctly. The bellows can be sealed to the valve in two different ways. First, the bellows can be welded to the valve stem at the top and the valve body at the bottom. In this case, the process fluid is contained in the bellows, or in the second method, the bellows is welded to the valve stem at the bottom and the valve body at the top. In this case, the process fluid is contained in the annular area (from the outside) between the valve cover and the bellows.

The bellows is the key component of the bellows sealing valve and the heart of the bellows sealing valve. In order to avoid distortion of the bellows, the valve must have a stem with only linear movement. This can be achieved by using a so-called turnbuckle in the bonnet yoke. The hand wheel is installed on the turnbuckle, which effectively converts the rotary motion of the hand wheel into linear motion in the valve stem.

Bellows type
There are two main types of bellows: forged bellows and welded bellows. Formed corrugated pipe is made by rolling a flat plate (thin-walled foil) into a pipe, and then longitudinally welding it. The tube is then mechanically or hydrostatically formed into a corrugated tube with circular and widely spaced corrugations. The welded blade type bellows is formed by welding a thin metal washer-like plate on the inner and outer circumferences of the washer-like plate. Compared with forged bellows, welded blade bellows have more folds per unit length. Therefore, under the same stroke length, the length of the forged bellows is two to three times that of the welded blade bellows.

According to reports, mechanically forged bellows fail at random points, while welded blades usually fail at or near the weld. To ensure complete penetration of the bellows end and end chuck welding, micro-plasma welding is recommended.

Bellows design
The multi-layer corrugated pipe is designed to handle high-pressure fluids (usually two or three metal walls). Compared with the single-layer corrugated pipe of the same thickness, the rated pressure of the double-layer corrugated pipe can be increased by 80% to 100%. Or, if a single-layer bellows with a thickness equal to the rated pressure of the two-layer bellows is used, the stroke length is reduced. Therefore, the multi-layer corrugated pipe design has obvious advantages over the single-layer corrugated pipe. Obviously, bellows are affected by metal fatigue, which can lead to welding failures. In addition to the influence of common parameters such as fluid temperature and pressure, the fatigue life of bellows is also affected by structural materials, manufacturing processes, stroke length and stroke frequency. Bellows material
The stainless steel bellows material is AISI316Ti, which contains titanium and can withstand high temperatures. Or, compared with stainless steel bellows, Inconel 600 or Inconel 625 has improved fatigue strength and corrosion resistance. Similarly, Hastalloy C-276 has higher corrosion resistance and fatigue strength than Inconel 625. The use of multiple bellows systems and reduced stroke length can improve the fatigue resistance of the bellows, thereby increasing the service life of the bellows.
www.hengjiafirefighting.com