Load factor k, load ratio (sealing force). The hydraulic load factor k is defined as the ratio of the hydraulically loaded area A_H to the sliding face A.

For externally pressurized mechanical seals the following applies:

A_H = (D² - d_H²) · p/4

D = external sliding face diameter

d_H = hydraulic diameter

A = (D² - d²) · p/4

d = internal sliding face diameter

For internally pressurized mechanical seals:

A_H = (d_H² - d²) · p/4

The hydraulic diameter d_H is calculated for metal bellows mechanical seals as follows:

da = external bellows diameter

di = internal bellows diameter

It must be noted, however, that the hydraulic diameter changes due to elastic deformation of the discs when subjected to pressure.

With k>1 the mechanical seal is said to be loaded, with k<1 it is said to be balanced. Load factors usually lie in the range k="0.6..." 2. As the value of k goes up, so the sealing face load rises, the sealing gap becomes narrower, the leakage decreases and the wear increases. As the value of k falls, the sealing face load decreases. This is why balanced mechanical seals are used for applications in the high pressure and high speed range. The falling value of k improves the formation of a lubrication film, but it also produces greater leakage. Too low a value of k due either to mis-setting or sealing gap distortions can cause separation of the sliding faces.

 

Mechanical seal with integrated balance step

Balanced mechanical seals require a balance step on account of the necessary difference in diameter between d_H and d. This balance step can be worked directly into the shaft (sleeve) contour or be integrated in the mechanical seal in the form of a shaft sleeve.