Closing force (sealing force) is the aggregate of the hydraulic force and the spring force, less the force in the sealing gap and the frictional force of the secondary seal of the seal face. It is a major factor determining the sliding pressure and hence the power consumption. Calculation formula:

F_SchI = F_H + F_F ± F_R - F_Sp

F_H (hydraulic force) = p₁ · A_H = p₁ · k · A

p₁ = pressure to be sealed

A_H = hydraulically loaded area

k = load factor

A = sliding face

F_F (spring force) = z · F_F

z = number of springs

F_F = spring force in installation length

F_R = frictional force of the secondary seal F_R is usually disregarded when designing a mechanical seal. F_R can become so great, however, e. g. through deposits upstream or downstream from the secondary seal, that F_Schl becomes negative and the seal opens.

F_Sp (force in the sealing gap)

= 2 p

d, D = inner, outer diameter of sliding face

p (r) = pressure characteristic in sealing gap