3.5.1 Hoses and flexible connectors
The simplest form of an flexible connection is the plastic hose. Larger nominal diameters are enhanced by inlaid metal spirals, to prevent a constriction. Their ends are clamped to hose adapters and secured with hose clamps. Since plastic outgasses in the vacuum, such hoses should only be used for low and medium vacuum applications. For pressures better than 1 · 10-4 hPa, metal hoses are essential. They are cold-formed from thin-walled tubes in the form of concentric shafts and welded to the flange connections to seal them hermetically. Annealed corrugated hoses are stress relieved by annealing after deformation and thus have a lower restoring moment. However, deformation causes further cold working and depending on the degree of deformation, it omits the stress relief annealing again. Thin-walled corrugated hoses are very flexible and easy to deform.
Corrugated hoses shrink under vacuum. Therefore flexible connectors may act as hydraulic elements. Depending on the axial spring rate and the hydraulic cross-section of their profile, axial forces are created, which are transferred onto the flange connections. Large nominal diameters create enormous tensile forces, which must be considered when designing a system. While corrugated hoses are mainly used to connect two flanges in a space, spring bellows are used for axial compensation or absorption of vibrations. Their profile is very flexible, as it is compressed in the form of an omega-wave.
Membrane bellows are made from individual lamellas welded together. On a short installation length it is possible to achieve long, axial strokes and large bending angles. Due to the rigidity of the lamellas, a lateral offset is only possible through relatively many membrane pairs which form an S-shaped profile.