The metallic flexible elements built up from multiple layers. This technically well considered construction has many advantages. For example much smaller spring forces occur than with single walled expansion joints. Very good flexibility at high pressures is guaranteed (the bursting pressure is at least three times higher than the nominal pressure). And also large movements are compensated despite the extremely compact design. But the elements are not able to sustain twisting, for such purposes it is necessary to choose a different design solution.


The metallic flexible elements with sizes from DN 6 to DN 300 are available in four basic versions, namely:

Type KBN 1 - standard hoses with central crimp and the average thickness of the rid;

Sizes from DN 6 to DN 150 are always in stock , DN 200 , 250 and 300 – on request .

Type KBN 2 – heavy duty hoses; mainly used for high pressure conditions, with one or two braids , out of stock , available on request.

Type KBN 3 - hoses with narrow crimp; applied in cases of small bending radius is required, out of stock, available on request.

Type ZW 22 - a hose with a double sidewall, is used in special cases of high dynamic stress, vibration etc., out of stock, available on request.


Because of the high movement absorption capability of the metallic flexible elements compared with single-walled bellows to take up movements resulting from heat expansion or vibration. In plant with restricted space often one is dependent on the use of multiply expansion joints. Costs are saved because of smaller face-to-face und outer dimensions of the bellows. The low displacement forces of the multiply expansion joints reduce the loading on the pipe fixation points, thus allowing cost savings with minimum space requirements. For example, articulated joint systems with minimum limb lengths.


For corrosion protection

Various materials can be used for the bellow to avoid the risk of corrosion. The anticorrosive barrier against aggressive media can be a single, relatively thin, and thus inexpensive, layer.


For overpressure

The Metallic flexible elements can be used for vacuum and for pressures up to for example 720 bar test pressure, depending on the diameter. With careful dimensioning and design the expansion joint can also be used for applications with external pressure.


For extreme temperature conditions

With appropriate material selection the flexible elements can be used for temperatures ranging between 220°C and 1100 °C. With suitable refractory lining - even higher temperatures are possible.


For vibration damping

Any kind of oscillation should be avoided because it generates noise and vibration. Oscillation is eliminated by two methods. In the first place, the source of oscillation has to be designed in such a manner that as little as possible oscillation is transferred to installations, connections, pipe lines etc.

The second place vibrating machines such as blowers and fans, compressors, combustion engines etc. can be isolated from other parts of the installation and buildings. Thus, vibration is not transferred to the whole plant and buildings. The multiple springs reduce structure-bom noise similar to rubber elements by up to 20 dBA.

Angular and pressure compensated flexible elements are technically the best oscillation dampers. Braces are placed in such a manner that any vibration must be eliminated over the bellows and cannot propagate via the pipe line.


In high and ultra-high vacuum applications

Special demands are set on purity of the used materials, the surfaces and welding methods. For this reason a thorough compliance with every single process steps and the used materials of the end connections determined by the customer have significant importance.


Specific requirements for surface quality are as follows:

  • gas tightness;
  • clean and smooth surface;
  • minimum foreign gas content;
  • low vapor pressure under all operating conditions;
  • Chemical resistance, temperature stability and mechanical stability may be additional requirements.


For the production of metal expansion joints used three basic types of material, namely:

  • For most of the bellows used materials DIN 1.4541; 1.4404 and 1.4571 (AISI 321, 316L and 316Ti).
  • Braid Material is DIN 1.4301 (AISI 304).
  • The material AISI 316Ti used for special applications.