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SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
GENERAL INFORMATION ON STUFFING BOX PACKINGS
Stuffing box packing materials:
Stuffing box packings can be braided, extruded, moulded or die-moulded. A braided
packing consists of a carrier (the base
material) and a lubricant and/or impregnating agent. The base material can be the
following:
Expanded graphite:
Supplied in the form of complete die-moulded stuffing box packing rings with different
densities, depending on the application
(pump or valve) and pressure. The material
is made of 100% natural graphite, which
is treated with acids and high temperature
according to a specially developed process.
The result is expanded graphite, which after
calendering, becomes a soft and flexible
foil that is used for manufacturing gaskets.
Characteristic of expanded graphite is its
broad temperature range from -200°C to
max. +2500°C in non-oxidising atmospheres and its media resistance, which
covers more or less all media with the
exception of strongly oxidising substances.
Another graphite packing variant consists of
braided strands of expanded graphite. This
packing does not include any lubricant or
filler material. A thin thread of cotton, carbon
fibre or Inconel is used as a carrier in every
strand. This type of stuffing box packing is
characterised by very good thermal conductivity and low friction. It is also self-lubricating and contains no abrasive particles. The
material is very elastic and also features
permanent recovery.
Carbon fibre:
Aramid fibre:
Stuffing box packing braid made of spun
carbon fibre with a minimum 96% carbon
content. This material is gentle on shafts
and shaft sleeves thanks to low friction.
Carbon fibre can be used for pumps and
valves for most media with a pH of 0-14,
with the exception of strong acids and alkalis and strongly oxidising substances. Some
variants are suitable for high temperatures
thanks to good thermal conductivity.
Braid spun from polyamide fibre yarn
(aramid or Kevlar®). The aramid fibre is
characterised by extremely high tensile
strength, which makes it suitable for use in
abrasive media or where there is a major
risk of particles entering the box. Can also
be used together with other fibre materials
as reinforcement in the corners of the stuffing box packing braid. Aramid fibres should
be used with care as there is a risk of e.g.
wear to the shaft or the sleeve.
PTFE fibre, filled:
Packing of PTFE fibre or expanded PTFE
fibre with different fillers. The most common
filler for stuffing box packings is graphite.
The fill level is approx. 50%. Graphite filler
gives the fibre very good thermal conductivity compared with pure PTFE fibre. The
low friction values of the PTFE fibre are
retained, as is its ability to withstand most
chemicals. The temperature and pH ranges
are the same as for pure, unfilled PTFE
fibre.
PTFE fibre, pure:
Stuffing box packing made of spun PTFE
yarn or expanded PTFE. These materials
are able to withstand most chemicals with
a pH of 0-14, with the exception of molten
alkali metals and fluorine. Some stuffing box
packings of expanded PTFE can also be
used for sealing off liquid oxygen and oxygen. PTFE fibres are also used for ozone
applications. The PTFE fibre is normally
temperature-resistant up to +200°C and
is capable of withstanding a max. surface
speed of 10 m/s. Suitable applications may
include pumps and valves with aggressive
or poorly lubricating media which do not
require good thermal dissipation.
Polyethylene fibre:
As a more modern alternative to aramid
fibre, there is now a special polyethylene
fibre with ultra-high molecular weight which
is particularly suitable for applications
handling abrasive media. This fibre is very
gentle on shafts and sleeves.
Other synthetic fibres:
Polyimide and acrylic fibres are examples of
other common synthetic fibres which are excellent for braiding for stuffing box packings.
Designed primarily for universal applications
at moderate pH values and temperatures.
Synthetic fibres conduct heat relatively
poorly, which means that the surface speed
should be kept moderate.
Lubricant, filler, special structure:
Special oils, waxes and solid lubricants
such as PTFE, graphite, silicone, molybdenum disulphide and mica may be included
in the packing in order to reduce friction and
improve resistance against various media.
Some packings also include a start-up
lubricant to facilitate the running-in of
pumps, agitators etc.
SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
Recommendations for material
selection:
The quick guide on choosing the right stuffing box packing and the respective product
pages contain information on the resistance
and applications of the packing materials.
However, the following factors should also
be taken into account when selecting stuffing box packings:
The most common braiding methods:
Square braiding:
Temperature limits:
The temperature limits specified in the quick
guide and in the respective product sheets
relate to the max. temperature of the stuffing
box packing during operation. Take into
account frictional heating, cooling, radiation
losses etc. when assessing temperature.
Medium:
Aggressiveness, pH, any solid particle
content, boiling point, solidification point,
viscosity and concentration are examples
of factors which may affect the choice of
packing.
The classic braiding method. Each strand passes over and under strands continuously in
the opposite direction. Packings braided according to this method are very well suited for
rapid rotations and reciprocating movements.
“Cover-on-cover”-braiding
Type of movement:
Rotating:
Braided packings are recommended.
Helical:
Braided packings are recommended.
Reciprocating valve stems:
Die-moulded graphite rings in combination
with a carbon fibre braided packing are
preferable.
Reciprocating piston pumps:
Braided packings are recommended.
The packing is built up to the required dimensions by braiding several covers over a core of
braided, twisted or homogeneous material. It is then calendered to create a square section.
Surface speed:
Observe the limits of the various stuffing
box packings in terms of surface speed.
Diagonal braiding:
Pressure:
The pressure of the medium against the
stuffing box packing affects the choice of
quality. See the relevant product pages.
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Interlock, Super-plait or Lattice-braid braiding are all examples of different methods of
diagonal braiding. This method results in a firm but flexible packing.
The strands run diagonally through the packing, thereby providing very smooth contact
faces and thus eliminating point loads on shafts and sleeves.
33
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SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
Q U I C K G U I D E o n c h o o s i n g t h e s t u f fi n g b o x p a c k i n g
Designation
Base material
Used for
Temperature range
Surface
speed
Max.
pressure
pH
Grafoil® rings
Die-moulded
expanded graphite.
Pumps, valves and agitators.
For most media such as gases, acids,
alkalis, petrochemical products etc.
-200°C to +2500°C in
non-oxidising atmosphere.
25 m/s
700 bar
depending on
application.
0-14
-
700 bar
depending on
application.
0-14
-
700 bar
depending on
application.
0-14
20 m/s
35 bar
in pumps.
0-14
Max. + 550°C in air.
Max. + 200°C in oxygen.
Garlock 9000 EVSP®
and Garlock 9001
QuickSet®
Die-moulded
expanded graphite/
carbon fibre. Profiled
rings.
Valve packing set suitable for most
media such as gases, acids, alkalis,
petrochemical products etc.
Max. +650°C in steam.
Specmaseal
Die-moulded
expanded graphite/
carbon fibre.
Valve packing set suitable for most
media such as gases, acids, alkalis,
petrochemical products etc.
Max. +650°C in steam.
Carbon fibre
impregnated with a
special lubricant.
Pumps, valves and agitators.
For virtually all media with the
exception of liquid oxygen and other
strongly oxidising substances.
Max. +650°C in steam.
Carbon fibre
impregnated with
PTFE. Interlockbraided.
Pumps, valves and agitators. Hot
and cold water, pulp, acids, alkalis,
oils, petroleum products etc. Not
oleum, oxygen, fuming nitric acid or
bichromates.
-100°C to +650°C.
Carbon fibre
impregnated with
graphite and corrosion
inhibitor.
Pumps, valves and agitators. Hot
and cold water, chemicals, alcohol,
solvents etc. Not liquid oxygen or
other strongly oxidising substances.
-240°C to +350°C.
Expanded graphite.
Square braided.
Pumps, valves and agitators. For
practically all media, but not for
strongly oxidising substances such as
conc. sulphuric acid and nitric acid.
-200°C to + 2500°C.
Pumps, valves and agitators. Very
aggressive media such as acids, alkalis
and petroleum products in e.g. the
petrochemical industry.
-200°C to +280°C.
Pumps, valves and agitators. Very
aggressive media such as acids, alkalis
and petroleum products in e.g. the
petrochemical industry.
-240°C to +260°C.
Garlock 98®
Carboflon 350
Specma 101
Grafex® 100
Chempac 2003
Specma 99
Gore® GFO fibre.
Interlock-braided.
Graphite-filled
expanded PTFE.
Interlock-braided.
Max. +450°C in oxidising
atmosphere.
Max. +450°C in oxidising
atmosphere.
Max. +450°C in oxidising
atmosphere.
170 bar
in valves.
25 m/s
60 bar
in pumps.
0-14
200 bar
in valves.
20 m/s
25 bar
in pumps.
0-14
300 bar
in valves.
Max. +650°C in steam.
30 m/s
30 bar
in pumps.
Max. +450°C in oxidising
atmosphere.
300 bar
in valves.
25 m/s
50 bar
in pumps.
0-14
0-14
250 bar
in valves.
20 m/s
35 bar
in pumps.
200 bar
in valves.
0-14
SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
Designation
Base material
Used for
Temperature range
Surface
speed
Max.
pressure
pH
Chempac 2006
Hard
PTFE fibre without
lubricant. Interlockbraided.
Pumps, valves and agitators. Very
aggressive media such as acids, alkalis,
petroleum products, foods, oxygen,
liquid oxygen, ozone etc. BAMapproved.
-200°C to +280°C.
5 m/s
50 bar
in pumps.
0-14
PTFE fibre with
lubricant. Interlockbraided.
Pumps, valves and agitators. Very
aggressive media such as acids, alkalis,
petroleum products and foods. FDAapproved.
-200°C to +280°C.
PTFE-impregnated
polyimide fibre.
Diagonal-braided.
Pumps, valves and agitators
for acids, petroleum products,
solvents, water etc. Very suitable for
abrasive media such as
thick pulp pumps etc.
-100°C to +260°C.
Graphite-filled
expanded PTFE with
twisted aramid fibre in
the corners. Interlockbraided.
Pumps, valves and agitators.
For most media such as acids, alkalis,
petroleum products. Excellent for
worn boxes.
-100°C to +280°C.
Specially impregnated
interlock-braided
packing of polyethylene fibre with
ultra-high molecular
weight.
Pumps, valves and agitators handling
abrasive media. Broad range of
media. Universal packing in industries
requiring white stuffing box packings.
-100°C to +260°C.
PTFE-impregnated
acrylic fibre. Interlockbraided.
Pumps, valves and agitators. Hot and
cold water, paper, sugar etc. Designed
for the paper, food and brewing
industries.
-100°C to +250°C.
Graphited glass fibre.
Square braided.
Primarily a static seal
or flue gases, hot air and
superheated air.
For use in covers, doors and flanges.
The packing can also be used in
valves.
Max. +550°C.
Chempac 2006
Soft FDA
Bluepack
Chempac 2002
WearPac
Chempac 1404
White
Specma 2027
400 bar
in valves.
8 m/s
50 bar
in pumps.
0-14
100 bar
in valves.
20 m/s
25 bar
in pumps.
0-12
200 bar
in valves.
20 m/s
70 bar
in pumps.
3-12
360 bar
in valves.
15 m/s
25 bar
in pumps.
1-13
100 bar
in valves.
15 m/s
50 bar
in pumps.
2-12
100 bar
in valves.
Max. +200°C in steam.
-
150 bar
4-11
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SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
G E N E R A L I N F O R M A T I O N O N S T U F F I N G B O X E S – different function principles
Function principle for various
stuffing box types:
A stuffing box normally consists of two to
six stuffing box packing rings (we normally
recommend 4-6 rings) which are compressed between an axially displaceable
gland and a bottom ring, Figure 1. Hence
the packing rings attempt to expand radially
and will exert a radial pressure (contact
pressure) on the shaft. Friction from the
surrounding housing and the plasticity of
the material mean that the contact pressure
is greatest at the gland and decreases
towards the bottom ring.
Contact pressure
on shaft
Gland
Bottom ring
Packing rings
Figure 1. Stuffing box with pressure distribution, not
taking into account fluid pressure.
Fluid under pressure will penetrate between
the packings and the shaft and form small
pockets of fluid. There are then two different
pressures to take into account, namely the
fluid pressure in the pockets themselves
and the contact pressure between the
pockets. For a stuffing box loaded with fluid
pressure, the contact pressure changes as
shown in Figure 2. The fluid pressure falls
through the stuffing box down to atmospheric pressure at the gland.
Without load from
fluid pressure
With load from
fluid pressure
Contact pressure
on shaft
Fluid
side
B
A
A direct consequence of the distribution
of the contact pressure over the length of
the stuffing box is that wear on the shaft is
greatest at the gland (at A in Figure 2). If
wear occurs at B, this is because abrasive
particles from the fluid penetrate into the
stuffing box.
The size of the leak is dependent on the
contact pressure, which in turn is regulated
with the axial gland load. There must always
be leakage so as to dissipate frictional heat
and prevent vaporisation of the fluid. The
magnitude of the leak for correctly functioning and adjusted stuffing boxes is 1-10 cm3
per minute, i.e. from a few drops per minute
to approx. 1 drop per second.
For a stuffing box with a lantern ring, the
pressure distribution is slightly different, see
Figure 3. The lantern should be added in
the middle of the box. When there are five
rings and a lantern ring, the ring should be
positioned with two rings inside and three
rings outside so as to prevent the lantern
ring moving too far axially when tightening
the gland and so running the risk of blocking
the supply of fluid.
Different stuffing box
arrangements:
Stuffing box without barrier fluid:
The pump medium forms a fluid film and
must be clean in order to keep wear to a
reasonable level. This version, Figure 4, is
able to withstand only moderate temperatures as heat transfer takes place only
through the leakage flow. This can be compensated to an extent by using a stuffing
box packing with good thermal conductivity.
There is a risk of air suction at low intake
pressures and negative pressure.
Figure 4. Stuffing box without barrier fluid.
Stuffing box with the pump medium
as barrier fluid:
The pump medium must be clean here,
too. The barrier fluid line is taken out from
a point where the pressure is higher than in
the box, thereby eliminating the risk of air
suction through the stuffing box.
Contact
pressure
on shaft
Atmosphere
side
Fluid
side
Lantern ring with barrier fluid
Figure 3. Pressure drop curve for a stuffing box with a
lantern ring.
Depending on the position and function of
the lantern ring, there are sometimes different designations for this ring, e.g. fluid seal
ring or barrier water ring.
Stuffing box with separate barrier fluid:
This version, Figure 5, is required for contaminated, hot and hazardous media. The
sealing fluid must be selected with regard to
the pumped medium and should maintain a
pressure which exceeds the pressure in the
sealing location by 1-1.5 bar. The amount of
sealing fluid leaking into the pump medium
is dependent on factors such as the shaft's
rigidity and roundness and is normally of the
order of just a fraction of a litre per minute.
Atmosphere
side
Figure 5. Stuffing box for barrier fluid with normal
position of the lantern ring.
Figure 2. Pressure distribution in a stuffing box.
SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
The best function is achieved with a flushed
stuffing box with barrier fluid intake and discharge, Figure 6. In this case, the barrier fluid
acts as both a barrier fluid and a coolant.
Stuffing box with cooling:
At fluid temperatures above 80-120°C, depending on packing material, type of media
etc., cooling of the stuffing box should be
implemented. Cooling outside the stuffing
box packing rings conducts heat poorly and
has a modest effect. Therefore, at higher
temperatures the cooling chamber should
extend inside the stuffing box packing rings,
Figure 8. At fluid temperatures above 130140°C, cooling of the gland should also be
implemented. An arrangement of this type
reduces steam leakage and prevents the
transfer of heat through the shaft to the front
bearing.
A flow control unit as shown in Figure 9 allows
you to control:
• leakage into the process
• fluid volume
• fluid pressure
• check the function of
mechanical shaft seals
• fluid loss (alarm)
A modular system allows
the unit to be adapted
readily to a type of box
or seal.
Figure 9.
Flow control unit
General information on valve stem
seals:
Figure 6. Stuffing box for barrier fluid with normal
position of the lantern ring.
In the case of extremely abrasive media,
the lantern ring can be positioned innermost
inside the box, Figure 7, in order to prevent
abrasive particles entering the box. In this
case, a considerable amount of barrier fluid
leaks into the pump medium.
Figure 8. Stuffing box with a cooling jacket and cooled
gland.
Controlling barrier fluid:
Selecting a cooling and barrier fluid system
correctly can reduce costs. This is achieved
by means of reduced fluid consumption,
because the seal and packing last longer,
reduced labour and spare part costs, lower
energy costs (as it is possible to make
sure that cold flushing fluid is not leaking
unnecessarily into the hot process media)
and less load on drains.
Stuffing box packings for sealing valve
stuffing boxes differ significantly from pump
and agitator boxes insofar as there is not
normally any major dynamic influence on
stems. Valve stems can have a rotating,
helical or reciprocating movement. One
thing these three movements have in
common is the fact that they are all relatively slow, which means that no fluid film
is required between the packings and the
stem. Valve stuffing boxes must always
be tightened to prevent drips leaking. See
also product information on Grafoil®-rings,
Garlock 9000 EVSP® and Specmaseal.
Tip for designers:
When designing stuffing boxes, we recommend dimensions,
tolerances and surface finish as shown in the drawing below:
Figure 7. Stuffing box for barrier fluid with the lantern
ring positioned innermost inside the box.
Number of packing rings: 4-6 pcs
Packing dimension:
Pumps:
Valves:
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SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
I N S T A L L A T I O N I N S T R U C T I O N S – s t u f fi n g b o x p a c k i n g s f o r p u m p s a n d v a l v e s
General:
The service life of your stuffing box packings can be extended considerably and the
total cost of new packings reduced significantly if you install and maintain your packings correctly. To achieve optimum operating results and the best possible economy
when working with stuffing box packings,
the following points therefore have to be
observed carefully.
General instructions for the installation of
stuffing box packings in pumps and agitators.
1. Removal, cleaning and checking:
Remove all old packing from the stuffing
box, including inside the lantern ring.
We recommend that you use a flexible packing extractor or a forged packing hook (Figure
1). Take great care not to damage the box
walls, shaft or shaft sleeves. Also check that
the sealing water ducts are not blocked.
2. Choosing the right packing dimension and
cutting to the correct length:
Use the right packing dimension in packing
sold by the metre or die-moulded rings. If
the measured width of the radial box area is
between two dimensions, choose the next
biggest packing dimension (Figure 2).
L = ( x 1.6 + Ø) x π
L = packing length
= packing dimension
Ø= Shaft diameter
D–d
= packing dimension
2
For large shafts and certain qualities, the value
1.6 can be replaced with a higher value.
Figure 3. Flattening a braided packing
3. Installation of stuffing box packings:
Install one ring at a time and push in each
ring using the gland and possibly also a split
sleeve until it bottoms out before installing
the next ring. Stagger the joints 1/3 of a turn
from one another (Figure 4).
Figure 4. The joints
are staggered by 1/3
of a turn.
Figure 2. Packing dimension.
Figure 1. Cleaning the stuffing box.
Check the runout of the shaft, and make
sure it is not worn or cracked in such a
manner as to jeopardise the function of the
packing. A pump shaft should not normally
have a runout in excess of 0.07 mm. Use a
dial indicator! Also check that the clearance
between the shaft and the bottom of the
box and between the shaft and the gland
does not exceed 0.5 mm radially (Figure 2).
Otherwise, and if the box is too deep (more
than 6 rings), we recommend a filler bushing
with the right clearance. The gland and box
bottom should be flat. Any conicity in the box
bottom is evened out using a washer made
of a suitable material, and any gland neck
conicity is machined to remove it.
At the same time, check the bearings by
lifting the shaft up and down. Replace worn
or bent machine parts. Lubricate gland bolts
with e.g. Grafex® GTL graphite paste.
If the packing braid is too big, it has to be
flattened. To do this, take a pipe or another
smooth, rounded tool and use it to compress the packing against a clean surface,
making dragging motions back and forth
(Figure 3).
Never hammer a packing as this risks breaking the fibre material. During installation, turn
the smoothed side towards the shaft.
After installing any lantern ring, a bottom
compression is carried out using the split
sleeve (Figure 5). Make sure that the
lantern ring is placed so that it can move as
far as possible axially into the box relative
to the sealing water channels as the gland
is adjusted.
Packing sold by the metre must always be
cut in separate rings. The packing must
always be at least 1.6 x the cross-section of
the packing longer than the circumference
of the shaft. This is so that the packing fills
out the box with no gaps between the ends.
For the best cutting results, use a Pack-Boy
packing cutter, which automatically provides
the right braid length and bevelled ends.
Most packing qualities should, however,
be cut to oversize for the best operating
results, as shown above.
When cutting, it is recommended that you
wind PTFE tape at the cutting point in order
to facilitate cutting and prevent fraying.
If the operating temperature of the packing
braid exceeds +280°C, we recommend that
you remove the PTFE tape before installation.
Figure 5. Compression of bottom rings using a split
sleeve.
Fit the rest of the rings as shown above.
Finally, tighten the gland nuts equally using
spanners so that all rings are fully compressed. Then undo the nuts and apply
them again with your fingers. The packings
are tightened gradually when the machine
operates.
SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
4. Running in packings:
• Check that cooling water and any barrier
water equipment is working (Figure 6).
Open the intake and outlet valves. Start the
motor.
• The box must never run dry due to the risk
of overheating, resulting in expensive replacement of sleeves or shafts and potential
production losses (Figure 8).
• In some cases, too great a leakage may
occur when the shaft is stationary which is
fine when the shaft is rotating. Never tighten
any such box when the shaft is not rotating
as this may they cause the packing to burn
when you start it up.
General instructions for the installation
of stuffing box packings in valve boxes
and other static stuffing boxes:
Figure 8. Never let the box run dry. The shaft starts to
rotate. It must be possible to see a leak here, otherwise
the packing will run dry and overheat.
5. Adjustment:
Figure 6. Check that the cooling and
barrier water system is working.
• If the stuffing box is not leaking, undo the
gland nuts until a dripping leak occurs
(Figure 7). If the leak is too great after startup, apply the gland with minor adjustments
at 5 to 6-minute intervals until the leak is
reduced to approx. one drop per second,
which is equivalent to approx. 0.04 litres per
hour.
Figure 7. Drop leakage. The pump medium is switched
on. The gland is lightly tightened.
• If the leak is too great, tighten the gland
nuts equally until the leak is dripping vigorously. Then make small adjustments at
intervals of at least 5 minutes until the leak
is dripping weakly (Figure 9). Never try to
tighten a packing all at once. If you do this,
you run the risk of applying it too tightly and
causing it to burn before long, so causing
leakage and potential damage to the shaft.
Remember, there must always be a small
drop leakage to indicate that the fluid film
between the shaft and the packings is intact
(Figure 10).
• Use the right packing quality. This is important so as to prevent corrosion damage.
• The packing is cut and fitted as shown
in the instructions above, although in this
case the box is tightened fully right from the
outset so there is no drop leakage.
• Tighten the stuffing box once the valve has
been commissioned, and add a further ring
if so required.
Packing cutter:
There are a number of aids on the market
for cutting stuffing box packings to the
right length in relation to shaft and packing
dimensions (Figure 11).
Heat
Figure 9. Reduce the drop leakage gradually. Heat is
generated and the packing rings settle. Monitor the
running-in process carefully.
Heat
Small leakage
Figure 10. Fine-tune the gland for optimum function.
Adjustment will ensure your box is adjusted correctly,
with low friction, little leakage and a long service life.
Figure 11. Packing cutter for stuffing box packing.
When cutting, it is recommended that you
wind PTFE tape at the cutting point in order
to facilitate cutting and prevent fraying.
39