Page 278 - The Tribology Handbook

Mechanical seals B24

Table 24.2 Special seals and additional design features
Feature Reason for inclusion Remarks

CERBMIC/PTFE SEAL Excellent corrosion resistance of Particularly suitable for chemical
components in contact with the applica tiom
fluid to be sealed
PTFE
1- BELLOWS~,PTFE COVERED SPRING

PRODUCT 5G

SPLIT SEAL Ease of replacement of wearing The splitting of both sealing
components components reduces allowable
performance and gives some
leakage

PRODUCT

SPLIT SEAL RING
______
To flush sediments and other debris On pumps with the seal on suction
FLOW CONTROLLER from the sealing zone and to pressure, a small flow of product
remove frictional heat. To keep from pump discharge is piped to
seals handling hot products cool. the seal, and returns to pump
To keep seals handling cold products suction through the balance holes
warm in the impeller. If the differential
head exceeds 15 m a flow controller
is needed to limit the flow rate.
This is only suitable if the product
is free of particles above 50 pm.
With dirty products a cyclone
separator should be used instead,
to provide clean product to the seal
and return dirty product to the
~FLUS~Y FLOW INLET suction

QUENCH QUENCH FLOW To remove or prevent the build up of Water flushing will generally remove
crystals or decomposition products crystal deposits and low pressure
on the atmospheric side of the seal steam will remove ‘coke’ from
hydrocarbons

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SAFETY BUSH (illustrated on diagram of To give extra protection in the event The bush is usually made of
balanced seal) of seal failure by reducing the non-ferrous material to reduce risk
pressure of the escaping product of sparking or seizure
AUXILIARY PACKING/back up seal Used instead of a safety bush when Usually consists of two turns of soft
conditions are so hazardous that a packing in an auxiliary stuffing
second or emergency safeguard box, or a lip seal of PTFE based
must be provided material
B24.2