Bellows for safety and control valves

Safety, long service life, and pressures up to 600 bar ....
The cross-section of a valve spindle bellows shows the multi-walled structure of the bellows. (PresseBox) (Pforzheim, ) Safety, long service life, and pressures up to 600 bar – these are the essential requirements that valve bellows must fulfil. They are mainly used in machine building and plant construction, but also in aerospace or atomic power technology. As an integrated functional elements, they reliably guarantee the seal tightness of valves in these areas.

Multiple walls as functional principle
The principle of multiple walls is based on the idea that the complete pressure-bearing wall is to be divided into many, thinner individual layers, thus considerably increasing flexibility. The compression resistance of a multi-walled bellows is identical with that of a singled-walled bellows of the same total wall thickness. The difference is in the flexibility. While flexibility progressively decreases towards immobility in the case of the single-walled bellows, the flexibility of a multi-layer bellows is retained, mainly depending on the existing number of layers. The single wall thickness and number of layers of the bellows are geared towards the respective application conditions. For high-pressure applications, for example, bellows with up to 12 layers are used. The single wall thicknesses used in the process range from 0.1 mm through 0.5 mm.

Small adjustment rates for precise safety
Especially in the area of safety valves, the precise response behaviour of the valve is decisive. In some areas of application, even the smallest changes in internal pressure necessitate a fast closing of the valve. In regard to speed and reactivity, valves whose bellows have low adjusting forces are used here. Particularly in highly sensitive areas, the use of multi-walled bellows enables the precise control and monitoring of processes.

ANSI or DIN – international markets
In addition to the European markets, shaped by DIN standards, the Asian and American regions are now increasingly demanding "Quality by Witzenmann." Instead of DIN, bar, and mm, products are designed and certified according to ASME Code in these areas. In order to serve these markets with suitable flexible elements, Witzenmann has developed an own ANSI valve series, from ANSI Class 150 to ANSI Class 2500.

Technical compendium - the Manual of Metal Bellows
This book contains everything important that there is to know about metal bellows. Here, the 252-page manual has been divided into two sections to provide a better overview: the first part introduces products and areas of applications. This part also contains information regarding the fundamentals of bellows calculation. The second part consists of tables. Here, the user finds all dimensions and performance data for corrugated bellows, diaphragm bellows, expansion cells, or thin-walled precision tubes of the widest product program of the industry.

Advantages at a glance:
Due to the construction of the bellows from many individual layers, the following particularly favourable technical properties result:
- Control of high pressures with excellent flexibility
- Large movement compensation in the case of small construction lengths and guaranteed
number of load cycles (usually 10,000 load cycles)
- Low adjusting forces
- Small external bellows diameter and, as a result, small
effective cross-sections for a low fixed-point load

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D-75175 Pforzheim
Ulrike Brandauer
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