Xylem 8200 Series Base Mounted Centrifugal Fire Pumps AC2675 REV.C - Manual (Page 17)

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.
17
The standard stuffing box consists of rings of
packing (see assembly section for number of
rings), a seal cage, a bushing and a gland. A
shaft sleeve which extends through the box
and under the gland is 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 9). 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
GAUGE
PRESSURE
REDUCING
VALVE
STUFFING BOX
FIGURE 9 – CONTROLLED PRESSURE
SYSTEM