Buying tips for bellows sealed valves
When the medium is toxic, volatile, radioactive, or extremely expensive and does not allow external leakage caused by reciprocating valve stems, bellows are often used to seal the valve cover. This special bonnet structure can protect the valve stem and valve packing from contact with the process fluid. At the same time, the standard or environmentally-friendly stuffing box structure is used on the bellows sealing element, which can avoid the disaster in the event of a bellows failure Sexual consequences. Therefore, pay attention to whether there is leakage at the packing of the valve stem. If the packing is leaked, the bellows valve may have problems.
First, the bellows structure
There are usually two types of bellows for regulating valves, one is mechanically formed, and the other is a welded sheet type bellows. The overall height of the welded bellows is relatively low, but due to its manufacturing method and inherent structural defects, the service life may be limited; compared with the overall height of the machined bellows, the reliability is higher and the life is longer long.
Second, the problems that should be paid attention to in the application
The pressure rating of the bellows seal decreases with increasing temperature. The bellows seal type should be carefully considered. Special attention should be paid to the correct use and maintenance after installation to achieve the longest cycle life.
Third, Typical bellows products
A straight-stroke valve body structure with a bellows seal on the bonnet and consideration of the corresponding factors can become a bellows seal valve.
(1) Bellows sealed small diameter single seat regulating valve
The valve body parts adopt HV3000 series small-diameter single-seat regulating valve, which is a high-performance upper guide structure regulating valve with a Cv value ranging from 0.01 to 1.4. Except for a slight increase in overall height and weight, other valve body data are basically the same.
2) Single-seat regulating valve with bellows seal
The valve body part adopts HV3000 series single seat regulating valve, which is an upper guide structure regulating valve, DN: 40 ～ 200. Except for the overall height and weight being slightly increased, other valve body data is basically the same.
(3) Bellows sealed cage type double seated regulating valve
The valve body parts adopt HV3000 series double-seat regulating valve, which is a pressure-balanced regulating valve, DN: 40 ～ 200. Except that the overall height and weight are slightly increased, other valve body data are basically the same.
Fourth, economic alternatives
For places where the requirements of wet chlorine (to solve the problem of corrosion resistance) are not particularly high, the method of “rotary valve + multi-stage packing” can be used. For example, a full-featured ultra-light control valve with multi-stage flexible graphite packing.
Post time: Nov-28-2019