Bellows are often used to seal valve covers when the medium is toxic, volatile, radioactive or extremely expensive to prevent leakage from the reciprocating motion of the stem. This special bonnet structure protects the stem and valve packing from contact with the process fluid, and uses standard or environmentally friendly packing box structure on the bellows sealing elements to avoid catastrophic consequences in case the bellows break down and fail. Therefore, attention should be paid to observe whether there is leakage at the filler of the valve stem. If the filler leaks, the bellows valve may have problems.

I. Structure of Bellows

There are usually two kinds of bellows for regulating valves, one is machined and formed, the other is welded sheet bellows. The overall height of welded sheet bellows is relatively low, but their service life may be limited due to their manufacturing methods and inherent structural defects. The machined bellows have higher overall height, but higher reliability and longer service life.

II. Problems needing attention in application

The pressure rating of bellows seal decreases with the increase of temperature. The bellows seal form should be carefully considered. After installation, special attention should be paid to correct use and maintenance so as to achieve the longest cycle operation life.

3. Typical Bellows

The bellows sealing valve can be made by using the straight-stroke valve body structure with bellows sealing top cover and considering the corresponding factors.

Pneumatic small caliber corrugated seal single seat valve

(1) Bellows Sealed Small Caliber Single Seat Regulating Valve

The valve body parts adopt HV3000 series small caliber single seat regulating valve, which is a high performance upper guiding structure regulating valve. The Cv value ranges from 0.01 to 1.4. Except for the slight increase of the overall height and weight, the data of other valves are basically the same.

(2) Bellows Sealed Single Seat Regulating Valve

The valve body parts adopt HV3000 series single seat regulating valve, which is a kind of upper guiding structure regulating valve. DN:40-200. Except for the overall height and weight slightly increased, other valve body data are basically the same.

(3) bellows sealed cage type two-seat regulating valve

The valve body parts adopt HV3000 series cage double seat regulating valve, which is a pressure balancing regulating valve. DN:40-200. Except for the overall height and weight slightly increased, other valve body data are basically the same.

IV. Economic Alternatives

For wet chlorine gas (to solve corrosion resistance) and other requirements are not particularly high occasions, can be used "rotary valve + multi-stage packing" to solve. For example, the use of multi-stage flexible graphite filler full-function ultra-light regulating valve.