Xylem 9100 Series Base Mounted Centrifugal Fire Pumps AC User Manual download pdf (Page 18)

is operating in conformance with the

performance curve. If cavitation, vapor

binding, or other unstable operation should

occur, widely fluctuating discharge pressure

will be noted.

Pump Insulation

On chilled water applications most pumps are

insulated. As part of this practice, the pump

bearing housings should not be insulated

since this would tend to “trap” heat inside the

housing. This could lead to increased bearing

temperatures and premature bearing failures.

16. STUFFING BOX LUBRICATION

Contaminants in the pumped liquid must not

enter the stuffing box. These contaminants

may cause severe abrasion or corrosion of

the shaft, or shaft sleeve, and rapid packing

or mechanical seal deterioration; they can

even plug the stuffing box flushing and

lubrication system. The stuffing box must be

supplied at all times with a source of clean,

clear liquid to flush and lubricate the packing

or seal. It is important to establish the

optimum flushing pressure that will keep

contaminants from the stuffing box cavity. If

this pressure is too low, fluid being pumped

may enter the stuffing box. If the pressure is

too high, excessive packing or seal wear may

result; and extreme heat may develop in the

shaft causing higher bearing temperatures.

The most desirable condition, therefore, is to

use a seal water pressure 15-20 psig above

the maximum stuffing box pressure.

17. 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 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

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Xylem 9100 Series Base Mounted Centrifugal Fire Pumps AC User Manual Page 18

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