TP50-160/2 Shaft Seals Manual

11
Shaft seals in general
Shaft seals
For unbalanced shaft seals, the following applies:
Key to symbols:
How does a shaft seal work
The functioning of a shaft seal depends on the forma-
tion of a load-carrying lubricating film between the seal
faces during pump operation. The lubricating film is
formed by the pumped liquid or an external liquid.
The load-carrying lubricating film is composed of a
• hydrostatic film
• hydrodynamic film.
The hydrostatic lubricating film is formed in one of the
following ways:
• during operation, the pumped liquid is pressed into
the gap between the seal faces
• during operation, an external liquid is pressed into
the gap between the seal faces.
The hydrodynamic lubricating film is formed by the
pressure generated by the rotation of the shaft.
The thickness of the lubricating film depends on pump
speed, liquid temperature, liquid viscosity and the axial
force of the seal.
As the shaft seal is pressed together axially, the leak-
age to the atmosphere is limited.
The sealing liquid in the sealing gap is constantly
replaced due to
• vaporisation of the liquid to the atmosphere
• the circular movements of the liquid.
Fig. 10
Shaft seal during operation
K Area ratio
A The hydraulically loaded area in mm
2
B Contact face in mm
2
TM02 6895 1903
K
A
B
----1 [-]>=
Hydraulic
force
Spring force
Lubricating film