A spring and seal assembly in metal bellows mechanical seals. Metal bellows are classified in rolled bellows and laminated bellows. In both types of bellows the functional principle is the same: The desired spring force is produced by pretensioning the metal bellows to a specific installation length. This is conditional on the wall thickness (and – for multiple wall bellows – on the number of layers), the number of corrugations, the length of the pretensioning displacement and the height of the corrugation profile. A generally valid, simplified model can serve to explain the hydraulic function of a metal bellows in a mechanical seal, without going into details of the bellows' inherent rigidity and shaping. The model is based on metal bellows seals of standard design.

d = inside dia. sliding face

D = outside dia. sliding face

d₁ = inside dia. bellows

d₂ = outside dia. bellows

d_H = hydr. dia. =

wall thickness (and - for multiple wall bellows - on the number of layers), the number of corrugations, the length of the pretensioning displacement and the height of the corrugation profile. A generally valid, simplified model can serve to explain the hydraulic function of a metall bellows in a mechanical seal, without going into details of the bellows' inherent rigidity and shaping.

The model is based on metal bellows seals of standard design.

Forces and area model with external pressurization of the corrugation pair with p₁

p₁ = pressure

A = area

F = force

A₁, A₂, A₃, A₄

= projected areas of the disc

because d_H = then:

A₁ = A₂ = A₃ = A₄

because p · A = F then:

F₁ = F₂ = F₃ = F₄

F₂ and F₃ are equal, face in opposite directions, and produce tension in the sheet metal and in the weld.

F₄ is conveyed through the outer weld into the bellows holder and from there into the corrugation. F₁ and F₅ face in opposite directions, F₅ < F₁. Hence F₁ - F₅ = F_H, the hydraulically closing force. It is this working principle that also allows hydraulically balanced mechanical seals to be mounted on completely smooth shafts, because the ratio of the hydraulically loaded (residual) face and the sliding face (load factor k) can be varied within wide limits.