TP100-80/4 Shaft Seals Manual

15
Shaft seals
Shaft seals in viscous
liquids
Shaft seals in viscous liquids
With the basic principles of the mechanical shaft seal in
mind, it seems logical that a high-viscous liquid creates
a thicker liquid film with better lubricating properties.
However, the following shaft seal problems may occur
when pumping viscous liquids:
• If it has a vapour pressure lower than that of water
at room temperature, the viscous liquid will not
evaporate. Consequently, it accumulates around the
shaft seal. This problem can be solved by using a
double shaft seal. For further information see
page 39.
• If the liquid contains solvents, these will evaporate
and leave an even more viscous liquid in the shaft
seal. This high-viscous liquid may precipitate a
coating on the seal faces causing leakage or abra-
sive wear. This problem can be solved by using car-
bide/carbide seal faces or a double shaft seal. For
further information see page 4 and page 39.
• Coolants such as glycols often contain additives
(corrosion inhibitors) that may precipitate and crys-
tallize on the seal faces causing abrasive wear.
Therefore it is recommended to use carbide/carbide
seal faces for all coolants. For further information
see page 4.
Recommended shaft seals for viscous
liquids
Seal face materials
It is recommended to use carbide/carbide seal faces for
viscous liquids. Grundfos carbide seal faces are made
of either silicon carbide (code Q) or tungsten carbide
(code U).
Seal faces made of impregnated carbon (code A or B)
are not recommended due to their lack of abrasion
resistance.
Surface pressure
To minimize precipitation, it is important to ensure a
high surface pressure between the seal faces. This can
be achieved by reducing the seal face area (R or G
seals) or by providing the seal with a tight spring. In
shaft seals with a high surface pressure the seal faces
have considerably smoother surface than ordinary
shaft seals.
Recommended shaft seal codes for viscous liquids
Description Shaft seal code
Type A seals
O-ring seal with fixed seal driver
AUUE
AUUV
AQQE
AQQV
Type B seals
Bellows seal with fixed seal driver
BQQE
BQQV
BUUE
BUUV
Type D seals
O-ring seal, balanced
DQQE
DQQV
Type E seals
O-ring seal, type A, cartridge
EUUE
EUUV
EQQE
EQQV
Type G seals
Bellows seal, type B, with reduced seal faces
GUUE
GUUV
GQQE
GQQV
Type H seals
O-ring seal, type D, cartridge
HUUE
HUUV
HQQE
HQQV
Type R seals
O-ring seal, type A, with redced seal faces
RUUE
RUUV