Goulds Pumps 3498 - IOM - Manual (Page 30)

One recommended method to minimize error in regulating
flushing water is a “Controlled Pressure System” (Fig. 13).
Most important is the pressure reducing valve adjusted to a
value slightly exceeding the maximum stuffing box
operating pressure (assuming it is reasonably constant). A
flow indicating device will serve to indicate a failing of the
bottom packing rings allowing leakage into the pump.
External sealing liquid should be adjusted to the point
where the packing runs only slightly warm, with a very
slow drip from the stuffing box. Excess pressure from an
external source can be very destructive to packing. More
pressure is required, however, for abrasive slurries than for
clear liquids. Examination of the leakage will indicate
whether to increase or decrease external pressure. If slurry
is present in the leakage, increase the pressure until only
clear liquid drips from the box. If the drippage is corrosive
or harmful to personnel, it should be collected and piped
away.
A common error is to open the external piping valve wide
and then control the drippage by tightening the packing
gland. Actually, a combination of both adjustments is
essential to arrive at the optimum condition. The life of
packing and sleeve depends on this careful control more
than any other factor.
MECHANICAL SEALS
!
The mechanical seal used in an ATEX classified
environment must be properly certified.
Mechanical seals are preferred over packing on some
applications because of better sealing qualities and longer
serviceability. Leakage is eliminated when a seal is
properly installed, and normal life is much greater than that
of 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
ordered from your Goulds Pumps 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 pumpage, an external
source of clean seal water must be supplied. Supply
approximately 0.5 - 1.0 GPM at a pressure approximately
15 to 20 psig above the suction pressure.
Fig. 13 shows the recommended "Controlled Pressure
System" for a mechanical seal. 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.
!
The mechanical seal must have an appropriate seal
flush system. Failure to do so will result in excess
heat generation and seal failure.
CYCLONE SEPARATOR
If the fluid being pumped contains sediment and there is no
external, clean water source available to flush the packing
or mechanical seals, a cyclone 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).
3498 IOM 12/04
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Fig. 13