TP32-80/2 Shaft Seals Manual

7
Shaft seals
Shaft seals in general
What is a shaft seal
A shaft seal serves as a barrier in pumps to separate
liquids or confine pressure.
How are shaft seals used
Shaft seals are used where the pumped liquid can dam-
age the motor.
Canned rotor type pumps have no shaft seals which
means that the pumped liquid is allowed to enter the
motor.
The photos below are examples of pumps incorporating
rotating shaft seals.
A rotating shaft seal is fitted in the gap between a rotat-
ing pump shaft and a stationary pump/motor housing.
Fig. 1
Shaft seal in a CR pump (in-line pump)
Fig. 2 Shaft seal in an NB pump (end-suction pump)
Rotating shaft seals
Rotating shaft seals are used where two pump compo-
nents move relative to one another. Rotating shaft
seals include mechanical seals and soft seals (stuffing
boxes, lip seals) among others.
Rotating shaft seals
• are exposed to a rotating movement
• form during operation a load-carrying lubricating film
between the seal faces of the rotating and station-
ary part of the shaft seal. For further information,
see "How does a shaft seal work" on page 11.
Fig. 3
Rotating shaft seal
In practice, no seal is completely tight. Leakage is influ-
enced by factors such as the ability of the pumped liq-
uid to penetrate the shaft seal, the fluctuating
hydrodynamic gap pressure between the seal faces,
the topo-graphy of the surface and the hydraulic closing
force.
It is essential that both static and rotating seals are not
only resistant to the liquid they are to seal against but
also capable of withstanding the impacts resulting from
the operation of the pump.
The choice of shaft seal depends on
• the liquid the seal is to seal against
• the liquid properties
• the mechanical, chemical and thermal impacts on
the seal.
GR5357 - GR3395GR2796 - TM02 7400 3503
Motor
Pump head
Base
Shaft seal
(cartridge type
Impellers
Motor
Pump housing
Shaft seal
TM02 6895 1903
Hydraulic
force
Spring force
Lubricating film