Xylem 8100 Series Centrifugal Pumps AC2515 REV.C - Manual (Page 18)

difficult. Consideration should be given to using a
mechanical seal. (See Mechanical Seals.)
Packing
Standard pumps are normally packed before
shipment. If the pump is installed within 60
days after shipment, the packing will be in
good condition with a sufficient supply of
lubrication. If the pump is stored for a longer
period, it may be necessary to repack the
stuffing box. In all cases, however, inspect
the packing before the pump is started.
NOTE: Packing adjustment is covered in the
Maintenance section of this manual.
On some applications, it is possible to use
internal liquid lubrication (pumped liquid) to
lubricate packing. Only when all of the
following conditions prevail, can this be done:
1. Liquid is clean, free from sediment and
chemical precipitation and is compatible
with seal materials.
2. Temperature is above 32°F and below
160°F.
3. Suction pressure is below 75 psig.
4. Lubrication (pumped liquid) has lubricating
qualities.
5. Liquid is non-toxic and non-volatile.
When the liquid being pumped contains
solids or is otherwise not compatible with
packing materials, an outside supply of seal
liquid should be furnished. In general,
external-injection liquid (from an outside
source) is required when any of the above
conditions cannot be met.
The standard stuffing box consists of rings of
packing (see assembly section for number of
rings), a seal cage (optional), and a gland. A
shaft sleeve which extends through the box
and under the gland is normally provided to
protect the shaft.
A tapped hole is supplied in the stuffing box
directly over the seal cage to introduce a
clean, clear sealing medium. The stuffing box
must, at all times, be supplied with sealing
liquid at a high enough pressure to keep the
box free from foreign matter, which would
quickly destroy the packing and score the
shaft sleeve.
Only a sufficient volume of sealing liquid to create
a definite direction of flow from the stuffing box
inward to the pump casing is required, but the
pressure is important. Apply seal water at a rate of
approximately .25 GPM at a pressure
approximately 15 to 20 psig above the suction
pressure. (Approximately one (1) drop per
second.)
One recommended method to minimize error in
regulating flushing water is a “Controlled Pressure
System” (Figure 14). It is important to set 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 detect a
failing of the bottom packing rings allowing
leakage in 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. A combination of
both adjustments is essential to arrive at the
optimum condition. The life of packing and sleeve
depends on careful control more than any other
factor.
FLOWMETER
PRESSURE
GUAGE
PRESSURE
REDUCING
VALAVE
STUFFING BOX
FIGURE 14 – CONTROLLED PRESSURE
SYSTEM
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