17
Figure 14 - Steam barrier flush system for double
mechanical seal
ATTENTION
Silicon carbide on silicon carbide seals are not
recommended for steam flushed applications.
Double mechanical shaft seals are not available
on the HP32 or HP34 size pumps.
3.12 SEAL MATERIALS
SEAL FACES
All primary seals are available with carbon on-
silicon carbide faces for non-abrasive fluids and
silicon carbide on-silicon carbide faces for
abrasive fluids containing crystals, powders or
particles or when no particles of wear can be
allowed to enter the pumped fluid. Silicon
carbide-on-silicon carbide seals are not
recommended for steam flushed applications.
Carbon on stainless steel single seals are
available for nonabrasive and lubricating fluids.
All secondary double mechanical seals are with
carbon on silicon carbide faces.
ELASTOMERS
Product contacting primary elastomers must be
selected to be compatible with the product and
the process operation.
Consideration must be given to chemical
compatibility, temperatures and material
standards. HP & LH pumps are available with a
range of elastomers:
Table 2- Elastomer approvals
Consult the supplier for more information.
3.13 END COVER RELIEF VALVE
HP & LH pumps can be fitted with a cover relief
valve which can be set to protect the PUMP
ONLY from overpressure.
ATTENTION
This valve is not designed to protect the system
or to provide long term by-pass of liquid.
If this is required then an IN-LINE relief valve
should be fitted which can by-pass the liquid back
to the suction vessel during overpressure
situations.
The maximum pressure rating of the pump is
stated on the nameplate.
The relief valve should be set so that it opens
before it reaches this pressure.
Be aware that there may be a piece of equipment
in the system that is limited to a lower pressure
than the pump. (See section 3.11 SEALS AND
FLUSHING)
If this is the case then the pump end cover relief
valve should be set so that the pump cannot
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