TP80-80/4 Shaft Seals Manual

Shaft seals
44
Selection of shaft
seals
Selection of the most suitable shaft
seal
The list of pumped liquids in a data booklet often indi-
cates several suitable shaft seals for the pumping of the
same liquid.
As the properties of the suitable shaft seals often differ,
the purpose of this section is to give an example of how
to select the most suitable shaft seal.
Example
The following data is assumed:
Application: Shaft seal fitted in boiler
feed pump, type CR
Operating pressure: 26 bar
Operating temperature: +115 °C
In the CR, CRI, CRN, CRE, CRIE, CRNE data booklet
only one shaft seal, HQQE, is recommended for
pumping boiler water. On the other hand the HQQE
shaft seal is not the only shaft seal available for this
pump and application. As will appear from the descrip-
tion of the various shaft seal types in this data booklet,
the following seal types are suitable:
• HQQE (recommended shaft seal)
•HQQV
•HUBE
•BUBE
•AUUE.
Comparing maximum operating pressures
Comparing the maximum operating pressure range of
the above shaft seal types, it appears that
• the HQQE shaft seal is suitable because the operat-
ing pressure of the boiler feed pump does not ex-
ceed the 30 bar maximum operating pressure of the
shaft seal, see "Grundfos type H" on page 33.
• the HQQV shaft seal is suitable because the operat-
ing pressure of the boiler feed pump does not ex-
ceed the 30 bar maximum operating pressure of the
shaft seal, see "Grundfos type H" on page 33.
• the HUBE shaft seal is suitable because the operat-
ing pressure of the boiler feed pump does not ex-
ceed the 30 bar maximum operating pressure of the
shaft seal, see "Grundfos type H" on page 33.
• the BUBE shaft seal is not suitable because the
maximum operating pressure of the shaft seal is
16 bar, see "Grundfos type B" on page 25.
• The AUUE shaft seal is not suitable because the
maximum operating pressure of the shaft seal is
25 bar, see "Grundfos type A" on page 24.
This leads to the conclusion that among the shaft seals
indicated, only the type H shaft seals, HUBE, HQQE
and HQQV, are suitable.
Comparing maximum operating temperatures
As the HUBE, HQQE and HQQV seals have different
secondary seal materials, the maximum operating
temperature of the seals may differ.
Position 4 of the shaft seal configuration, for instance
HUBE, shows the secondary seal material. For further
information see page 6.
Shaft seals with an EPDM secondary seal resist water
temperatures up to +140°C, see "EPDM" on page 23.
Shaft seals with an FKM secondary seal resist water
temperatures up to +90°C, see "FKM" on page 23.
This leaves only two suitable shaft seals, HUBE and
HQQE.
Resistance to abrasive particles
The high pumped liquid temperature above +60°C may
cause lime to precipitate in the pumped liquid resulting
in scale formation. Deposits on the seal faces may
result in wear and reduced seal life.
According to the Grundfos type designation, the HUBE
seal face material combination is tungsten carbide/
carbon, see page 5. This tungsten carbide/carbon
material combination offers low-noise operation.
However, the deposits between the seal faces will lead
to reduced seal life.
The HQQE seal face material combination is silicon
carbide/silicon carbide (SiC/SiC), see page 5. Under
the operating conditions in this example, the SiC/SiC
material combination offers long life as compared to the
HUBE seal. However, the shaft seal will emit more
noise on account of the materials used.
Finally, the shaft seal that best matches the require-
ments of the particular application is to be selected:
As a boiler feed pump is usually not located in noise-
critical environments, an HQQE shaft seal is preferred
on account of its long life. If an HQQE shaft seal is
selected, a higher noise level must be accepted.