Xylem 8100 Series Centrifugal Pumps AC2515 REV.C - Manual (Page 19)

Mechanical Seals
Mechanical seals are preferred over packing on
some applications because of better sealing
qualities and longer serviceability. When a seal is
properly installed, it will last longer than packing
on similar applications. A mechanical shaft seal is
supplied in place of a packed stuffing box when
specifically requested. The change from packing
to an alternate arrangement may be made in the
field by competent service personnel. Conversion
parts may be order from your AC Fire Pump Sales
Representative.
Just as with packing, the mechanical seal
chamber must be supplied, at all times, with a
source of clean, clear liquid to flush and lubricate
the seal. The most important consideration is to
establish the optimum flushing pressure that will
keep contaminants from the seal cavity. If this
pressure is too low, fluid being pumped may enter
the stuffing box. If the pressure is too high,
excessive seal wear may result.
When contaminants are present in the system
fluid, an external source of clean seal water must
be supplied. Supply approximately .25 GPM at a
pressure approximately 15 to 20 psig above the
suction pressure.
Figure 14 shows the recommended flush system
for mechanical seal. Water enters the seal
chamber, lubricates the seal face, and exits into
the pump itself. Positive flow in the seal water line
indicates adequate seal water pressure.
Cartridge Seals
Follow the appropriate lubrication directions for
mechanical seals given in this section. Most
cartridge seals provide flushing connections on
their glands. Use the cartridge seal gland flushing
taps (if provided) for your seal water connections
instead of the stuffing box tap. The quench taps on
the glands (if present) are normally only used in
chemical applications. Consult seal manufacturer’s
literature for more detailed information.
Cyclone Sediment Separators
If the fluid being pumped contains sediment and
there is no external, clean water source available
to flush the mechanical seals, a cyclone sediment
separator can be used to remove most of the
sediment from the liquid being pumped so it can
be used to flush the seals. The separator is placed
in the seal water piping line and removes the
sediment to an external drain (normally back to the
pump suction line).
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