MMTC Packing

8/6/2019 MMTC Packing

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Packing

John Crane

Mechanical MaintenanceTraining Center


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Compiled by

John G. Ciffone, Director

Mechanical Maintenance Training Center

November 1994


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Packing 1

Packing

Packing as a seal is the throttling or restriction of leakage between a moving and stationary part. This motion

can be rotary, reciprocating, helical or swinging rotary.

One or more of these motions occur in pumps, valves, compressors, cylinders, presses, blowers, fans,autoclaves, mixers, condensers, or heat exchangers. In some, the amount of motion is almost imperceptible,

such as the movement of a tube within the tube sheet in a heat exchanger. On the other hand, motion inpumps can be fantastically high, as in centrifugal pumps where peripheral speeds of 7000, 8000 and 10,000fpm are encountered.

Add to this factor of speed the problems of temperature, pressure, and possible chemical action of the liquids

or gases being handled, shaft runout or gyration, misalignment of shafts and rods, coupled with the possibilityof scored or grooved shafts or rods, and an engineering problem is created.

John Crane has carefully considered these and other pertinent operating conditions in selecting - from themany available materials and designs - those which will do the best job in a specific application.

Packing may be classified either by method of operation or by materials and technique of construction. Theterms compression, automatic and floating packings refer to modes of operation. But when discussingconstruction, a classification by material and technique of manufacture is more convenient. Accordingly, the

packings will be classified as fibers, foils and elastomers, with subclassifications dealing with lubricants,binders and strengtheners.


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Compr ess ion, Autom at ic , and Float ing Pack ing

Compression PackingCompression packing gets its name from the fact that

to create an effective seal, it must be squeezedbetween the throat of the stuffing box and the gland.

Under these conditions, the packing flows outward toseal against the bore of the stuffing box and inwardto seal against the moving shaft or rod. Compression

packing requires adjustment to compensate for wearand loss of volume. This type of packing is found

mainly in rotary or centrifugal service and valvestems. Under certain conditions compression

packing is also used on reciprocating applications,but reciprocating motion is primarily handled by theautomatic type of packing. For some pump designs,

the packings are not only a sealing device, butadditionally considered and engineered to be a load

bearing device.

Automatic PackingAutomatic packing (hydraulic)depends on operating pressures to

create a seal and, thereforerequires little or no gland

adjustment. This design makes useof a flexible lip to seal against one

or both surfaces in the stuffing box.With V-rings and U-cups, one lipseals against the stationary bore

and the other against the moving

part. In the case of a piston cup orflange packing, the lip seals againstthe moving part only.

O-rings, T-rings, and quad-rings are a form of squeeze type packing. They also utilize pressure tocomplement their sealing ability and therefore their inclusion in the automatic category. These types of rings

are usually found on reciprocating applications or valve stem applications. While the automatic type packingssuch as V-rings are occasionally used on rotary or centrifugal applications, they are not normally

recommended because of their inability to withstand centrifugal speeds. They do not offer support of a shaftwhich is many times necessary.

Floating PackingThe third type of packing is the floating type which

includes piston rings and segmental rod packings. Allof these work in grooves, usually individually. They

work by some means of external force, either bymetal or rubber springs. These are found often in

compressors and turbines rather than in pumps orcylinders.

2 Packing

Figure 1 - Compression Packing

Figure 2 - Automatic Packing

V-Rings

O-Ring

Braided Packing Rings

Figure 3 - Floating Packing

Segmented Rod Packing


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Packing 3

Figure 4 - Packing Types

Compression Automatic Floating

11

3

3

2

2Braided Fabrics

Plastic

Metal Foil

Ribbon Foil

V-Ring

U-Cup

Piston Cup

T-Ring

O-Ring

Rod Packing

Piston Ring


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4 Packing

Pack ing Mater ia ls

Mechanical packings are required to operate in a wide variety of conditions: acids, alkalies, cryogenics, food

service, hydrocarbons, steam, any fluid or gas that can be compressed, controlled, or pumped. Combinedwith other application factors such as fpm and pressure, the required list of materials is lengthy. Materials areclassified by their source and duty.

Animal fibers such as hair and wool are often used for low pressure viscous service. Leather is often

impregnated with elastomers, oils, and waxes to be used as gasketing or automatic packing. Cotton, flax, juteand ramie are vegetable fibers used in water service because of their high wet strength. Another vegetable

fiber, paper, is often used as gasketing since it may be cut into detailed shapes. Mineral fibers such ascarbon, glass, and graphite have been proven effective under extreme pressure and temperature

applications. Packings of asbestos are not available from John Crane Inc. A wide variety of metallic foils intwisted or wrapped form are used. Foils are often used in extreme abrasive, corrosive, pressure,temperature, and viscous conditions. Synthetic materials such as aramid, acrylic and PTFE offer resiliency

along with resistance to pH extremes. Many of the synthetics can be used in temperature extremes. With awide range of capability, the synthetic packings are becoming universal service packings.

In the manufacturing process a variety of lubricants are added to packing. As with any lubricant, its primarypurpose is material separation and heat removal. In specific applications, the selected lubricant must also beinsoluble, non-corrosive, non-contaminating and non-solidifying. Lubricants are classified by their source:animal, vegetable, mineral, and synthetic. Lubricants that are dry, in powder form, are also used. Just as the

base material of the packing must be matched with an application, so too must the lubricant. Zinc powder isapplied to some packing styles for use as a sacrificial metal inhibitor to retard damage to valve stems.

Passive inhibitors such as phosphorous or barium may be also added to packings to retard corrosion.

Binders such as grease, PTFE, and waxes help maintain construction integrity and prevent fiber dispersal. Toadd strength to a packing, wires are inserted during the manufacturing process. Matching the application,wires of brass, copper, Inconel, Monel, and steel can be selected. Wire proves to be a significant aid in

high pressure and temperature situations.

Elastomers are common materials for both compression and automatic packings. They are often mixed withanother material or are homogenous. Elastomers add strength, and chemical and temperature resistance.

Elastomeric automatic packings such as U-cups, V-rings and O-rings are common mechanical sealcomponents.

Compr ess ion Pack ing Const r uc t ion Designs

The construction of packings is also a reference to its manufacturing technique. Perhaps the most commonconstruction form is the braid. The interwoven braid offers the most strength. The number of strands used

determines strength. The plaited braid uses few strands and is, therefore, a loose braid and not as strong asthe interwoven braid. Plastic packings are loose fibers combined with binders. This form will deform and takeshape in the stuffing box to fill any incongruities. Compressed graphite foils are also plastic in nature and will

also deform. Construction involving the wrapping of a material around a core is for resiliency and strength.

Metallic foils are often twisted around a core for strength and hardness. Packing rings with angular shapessuch as wedges, cups and cones compensate for any shaft or stem deflection. These rings are typically die-formed rings.


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Packing 5

Figure 5 - Packing Materials

Fibers

Animal

hairleatherwool

corkcottonflax

jutepaperramiewood

acrylicaramidfiberglasspolyimidePTFErayon

asbestos*carbonglassgraphitefiberfrax

metal

aluminumbabbittbronzecopperInconeliron

leadMonelnickelsilverstainless steelzinc

* Not available from John Crane Inc.

Lubricants

beeswax

fish oilglycerollanolinlard oilsoaptallow

castor oilcottonseed oillinseed oilpalm oil

fluorolubesoilssiliconeswaxes

greasesmineral oilparaffinpetrolatumpetroleum oil

waxes

Metals Elastomers

Vegetable

Animal

Vegetable

Synthetic Synthetic

Mineral

Foil Elastomers

Mineral

chloropreneethylene propylenefluorocarbonnitrileperfluoroelastomer

siliconestyrene butadine

Dry Lubricants

Powder carbongraphitemicamolyPTFEtalc

Plastic

Binders

elastomersgreasePTFEresinswaxes

Strengtheners

Wire brasscopperInconelMonelstainless steelzinc

Inhibi tors

Powderbarium molybdatephosphoruszinc


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6 Packing

Wedge

Hollow Center

Soft CoreWrapped Weave

Laminated

Cross Expansion

Interwoven Braid

Interwoven Braid

Wire Inserted

Plastic Square

Cup and Core

Soft Core

Braided CoreWrapped Weave

Laminated

Wedge

Square Wrapped

Foil

Combined

Interwoven Braid

Square Compressed

Ribbon Foil

Conical

Soft Core

Accordion Weave

Soft Backwith Braid

Soft Core

and Wedge

Mesh Core

Foil Wrapped

Plaited Braid

Flat / Sheet

Gasketing

Figure 6 - Compression Packing Designs


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Packing 7

Funct ion and Ar rangement

Conventional packings for pump applications are intended to throttle or restrict leakage, not stop leakage

completely. In order to operate properly, packings must be installed and maintained properly, and theirintention understood.

Packing must leak for lubrication and heat removal. A steady flow of drops along the shaft, typically 60 dropsper minute, is typical. The exact drip rate is adjusted by the temperature of the drops. Some applications will

require the use of a lantern ring, however this does not change the fundamental operation of packing. Figure7 (without a lantern ring) and Figure 8 (with a lantern ring) show correct installation and operation of the

packing arrangement. In both figures, leakage only occurs along the shaft where heat is generated. Tightsealing occurs at the bottom of the stuffing box and at the outer diameter of the packing rings and gland.

Initial installation of the rings requires that the first ring seals tight at the bottom of the stuffing box. The glandmust also be properly positioned, a minimum 1/8" into the stuffing box. The portion of the gland remainingoutside will equal the width of one ring for future tightening. As packing wears, the drip rate increases,

requiring adjustment of the gland. The gland is gradually tightened until the drip rate reduces to the approvedamount. Eventually, after several of these cycles, the gland will mate against the housing preventing further

adjustment. At this point excessive leakage may occur, and the packing set is worn out and must be

replaced.Figure 7 - Correct Installation Operation

Pumped

Fluid

Housing

Gland

Atmosphere

Begin at 60 drops per

minute (start up)

Bottom / Throat Face

Cooling and Lubrication

Impeller

Figure 8 - Correct Installation Operation With Flush

Pumped

Fluid

Impeller

A

Lantern Ring

Flush injection pressure higher than A


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8 Packing

Incorrect packing installation will lead to excessive leakage and wear. Figure 9 reveals problems that canarise when the first packing ring is not properly seated. A gap exists between the ring and stuffing box bottomwhich allows distortion of the rings and leakage along their outer diameter. Installing each ring, individually,

with a split bushing ensures proper seating radially and axially. Using incorrect tools, such as a screwdriver,will not achieve proper seating.

Pumped

Fluid

Impeller

Abrasion

Excessive

Leakage

Figure 9 - Incorrect Installation Operation

Figure 10 - Incorrect Installation Operation

Pumped

Fluid

Impeller

Shaft and Stuffing Box Abrasion

Flush Injection Blocked

Excessive

Leakage

After a packing set is worn out, with the gland no longer adjustable, the entire set must be replaced. Figure10 shows the common practice of installing additional packing rings, or just replacement of the outer rings.

This practice leads to problems. The innermost rings will be forced below the stuffing box, causing wear. If alantern ring is included in the set, it will be forced to an incorrect position and the flush injection port will be

blocked. While this practice is often done to save time, the damage it causes leads to future equipmentdowntime and component replacement costs.


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Packing 9

Overtightening packing can lead to premature failure. Many packing styles have been saturated withlubricants to prevent the packing from drying out. Figure 11 illustrates the four stages of failure due to

overtightening.

A. The packing is compressed into the stuffing box with leakage allowed along the shaft. If the rings are

overtightened, the lack of leakage allows the rings to become dry and frictional heat remains in thepacking area.

B. Excessive heat causes the saturant to melt out.C. At this point the packing can burn and lose construction integrity. The shaft can also overheat, distort

and score. Scoring is actually the loss of material, which then allows leakage to occur along the shaftproviding temporary lubrication.

D. The packing is totally compressed and leakage can no longer be controlled. As previously stated,packing is designed to throttle or restrict leakage, not stop leakage altogether.

Flush In ject ions and Lant er n Rings

Flush injections are used to "cool" and "clean" the packing arrangement when the characteristics of the fluidbeing pumped are not well suited to good packing performance. Perhaps the most common characteristics

are abrasives and pH extremes. The flush fluid, injected to the shaft at a higher pressure than pumped fluid,would force away from the packing abrasives, acids and alkalies. The flush fluid must be compatible with thefluid pumped, as it will enter that stream. Figure 8, page 7, shows a flush and lantern ring arrangement which

forces the pumped fluid away from the packing set, lubricates the rings, and prevents air from entering thepump.

The lantern ring simply provides a path for the flush fluid to reach the shaft. For correct performance, the

lantern ring must be located in line with the injection port. Lantern rings that are out of position are typicallydue to incorrect initial installation or the practice of installing additional packing rings into the stuffing box

beyond original engineering requirements. Lantern rings are either solid (endless) or split. Solid lantern ringsrequire equipment disassembly for removal and installation. Split lantern rings separate for removal andinstallation. Lantern rings have a loose inside and outside diameter fit. Lantern ring widths are typically equal

to 1-1/2 times the packing cross section.

Figure 11 - Stages of Failure

COMPRESSION

COMPRESSION COMPRESSION

COMPRESSION

A. New packing

C. Temporary fluid leakage

B. No fluid leakage -

saturant oozes out

D. No saturant left


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10 Packing

Flush Injection

Impeller

Abrasive

Pumped

Fluid

Lantern Ring

Quench Drain

Figure 12 - Abrasive Service Operation / Quench Gland Arrangement

Flush Injection

Impeller

Pumped

Fluid

Lantern Ring

Figure 13 - Outboard Lubrication / Air Prevention Arrangement

Impeller

Pumped

Fluid

Hard Ring Graphite Ring

Figure 14 - Combination Set Arrangement


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Packing 11

Spec ia l Ar r angement s

Figure 12, page 10, has the lantern ring located at the throat of the stuffing box. This arrangement is for

extreme abrasive service. The clean flush injection fluid washes abrasives away from the packing set. Alsoshown is a quench smothering gland which is somewhat rare in industry use today. These types of glandswere used prior to the refinement of mechanical seals in applications involving hazardous materials, pH

extremes, or fluids that flash to a gas when exposed to atmosphere. A suitable quench fluid is circulatedthrough the gland which mixes with the pumped fluid and is carried off for safe disposal. Currently, these

glands are only used for a drain port to carry away safe fluid leakage for disposal.

Figure 13, page 10, has the lantern ring located farther to the atmospheric side of the stuffing box. The flushinjection lubricates the outboard packing rings and prevents air from entering the pump.

Figure 14, page 10, shows rings of alternating material. Combination sets are used in applications such aspH extremes and radioactive service. Rings of pure graphite are employed due to their ability to fill

incongruities in the shaft and housing, in addition to their chemical and radiation resistance. Hard rings (bullrings) are used to prevent extrusion of the softer graphite packing material. Where combination sets are

necessary, pre-cut and formed ring sets are available. More detailed engineering and material selection

considerations are involved in these applications.

Pum p Pack ing Selec t ion Cr i t er ia

CONSIDER...

1. Liquid being handleda. Clean or abrasive?

b. pH - acid or alkaline?c. Can dilution be tolerated?

2. Mechanical conditionsa. Is equipment in good condition?

b. Shaft speed and materialc. Stuffing box dimensions

d. FPM limit (RPM x I.D. x 3.14 12 = FPM)e. Type of motion - rotary or reciprocatingf. Alignments

g. Pump design

Desirab le Proper t ies o f Pack ing

1. The packing should be sufficiently plastic to conform to the shaft and bore under gland pressure.

2. It should contain nothing that can be dissolved, swelled, or weakened by pump fluid.

3. It should be sufficiently elastic to absorb any shaft gyration that cannot be eliminated by equipmentdesign.

4. If tightened too much, it should possess the means of freeing itself without producing destructive frictionand heat.

5. It should not abrade or corrode the shaft or rod.

6. It should lose volume slowly so as not to require frequent adjustment.

7. It should be able to withstand high temperature and pressure.

3. Operating Conditionsa. Suction, discharge and box pressuresb. Temperature range

c. Service cycle

4. Special; requirementsa. Allowable leakage rate

b. Governmental regulations


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12 Packing

Pow er o f t he Hydrogen Ion Conc entr a t ion

The pH value of an aqueous solution is a number describing its acidity or alkalinity and is a factor in theselection of packings. The letters "pH" are an abbreviation for POWER OF THE HYDROGEN ION

CONCENTRATION.

Simply explained, pH is a method of describing the acidity or alkalinity of a substance. The figures used toexpress this property range from 0 to 14. For water, pH 7 is defined as the neutral point and the figures

above and below denote the degree of acidity or alkalinity.

The usual range of pH found in industry is from about 1 to 13. The pH of potable water is usually between 7

and 8.5 depending upon local and state regulations.

It is important to note that the intervals on the pH scale are exponential and therefore represent vastly widerdifferences in concentration than the figures themselves would indicate. The following table graphically

illustrates the exponential nature of pH values.

14 (Excess of Hydroxyl Ions) (OH)

13

12

11

10

9

8

7 (Distilled Water)

6

5

4

3

2

1

0 (Excess of Hydrogen Ions) (H)

10,000,000

1,000,000

100,000

10,000

1,000

100

10

1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

Alkalai

Neutral

Acid

Table 1 - pH Scale

Ratio of Hydrogen or Hydroxyl Ions Concentration to that of Pure Water

pH Value


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Packing 13

Pack ing Stora ge and Iden t i f i ca t ion

In the past John Crane manufactured over 300 packing styles. Recent developments in new materials andtechnologies have reduced that number. All packing applications can now be served with approximately 50

styles of the Rite Pak or Engineered series of packings. The packing style differences are in materials,

lubricants, binders, designs, and construction. It is nearly impossible to distinguish one packing style fromanother visually. Often overlooked are the storage and identification of packings which can be significant inthe performance of the packings.

Packing is supplied in two basic forms: die-formed pre-cut rings and bulk form lengths. Die-formed rings aretypically supplied in a plastic bag within a labeled box. Bulk form packing is wound on a spool in a labeled

box.

The plastic bags retain the lubricants in the packing and keep the packing clean. The box helps maintain theintegrity of the packing. The box has the identification label. The label will show the packing style number,

materials of construction and application range. Often the bulk form spools are not labeled. It is thereforecritical to keep the spools in the labeled box. Packing lengths should be properly maintained on the spool.The packing is wrapped on the spool with the cross-section reduced direction out from the spool centerpiece

bar. To maintain the wrap on the spool, the packing is pinned in position. Installation instructions are includedin the box.

Simple Rules to Follow1. Keep packing lengths "pinned" on the spool.2. Keep packing in the plastic bags.

3. Keep packing in the protective, labeled box.4. READ THE INSTRUCTIONS that are in the box.

5. Dispose of any packings not properly stored and identified.

Rite Pak

PackingStyle C1055

A

Services

Valve stems or rotary pump appli-cations, specifically for use in food

service. Materials used in the con-

struction of this style have approval

of the FDA. temperature to 500F

(260C), pH range 3 - 10.

Material

A special PTFE yarn impregnated

with a special approved lubricant for

food service.

.375 12

John Crane Inc.

6400 West Oakton Street

Morton Grove, IL U.S.A. 60053MADE IN U.S.A.

John Crane

Trademark

for bulk styles

Identification

ordering and

stocking style

number

ServiceInformation

Packing

Material

Box/Quantity Size

Industry Use Symbol

Amount on Spool

Cross Section Size

Figure 15 - Label Information


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14 Packing

Desired St uf f ing Box Condi t ions

The successful service life obtained from packings is directly related to the finish of the housing bore andshaft. Proper clearances are also important, particularly in high pressure applications. Tighter clearances

provide better support for the packings and help throttle leakage. Suggested general finishes and clearances

are shown below.

Figure 16 - Desired Stuffing Box Conditions

A

A

B

C

DE

F

B

C D

E

F

Impeller

Housing

Gland

Shaft / Sleeve

Shaft finish: 16 - 20 microinches

Bore finish: 50 - 75 microinches

Throat / Shaft clearance: .005 - .015

Gland / Shaft clearance: .010 - .030Gland / Bore clearance: .010 - .030

Metallic Packings, Brinell hardness 500 (Rockwell C 55 - 60)


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Packing 15

Measurements

Determining ring cross-section size:1. Measure stuffing box bore "A".2. Measure shaft/sleeve diameter "B".

3. Subtract shaft from bore "A" - "B".4. Divide that difference by 2.

A-B = Cross section2

Determining ring quantity:1. Measure stuffing box depth "C".

2. Divide "C" by cross-section.C = rings required.

CROSS SECTION

3. If the number of rings results in a fraction greater than 1/4", add a ring.

4. If a lantern ring is used, subtract two rings.

Gland positions:1. Measure gland height "D".

2. After installing packing rings, tighten gland so that 1/8" to 3/16" of "D" is into the stuffing box.3. Portion of "D" out of the stuffing box should equal one ring cross-section, for maximum

future tightening.

Space Available:1. Measure nearest obstruction "E".2. "E" dimension determines length of split bushing for ring installation.

C

E

A B

D

Figure 17 - Measurements


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16 Packing

Pac k ing Cross Sec t ion Size

Most compression packing cross sections appear to have a square shape.

However, in reality the cross section has a rectangular shape. The cross section

is reduced in one direction for easier installation of the ring into the stuffing box.

The reduced direction fits between the shaft and stuffing box bore. The crosssection reduction eliminates the practice of "hammering" the packing for

installation. "Hammering" will break the packing fibers and increase the overall

ring length. Too long a ring will cause "hot spots" along the shaft in service. Bulk

form packing on spools are wrapped on the spool so that the reduced direction of

the cross section faces up. The centerpiece bar of the spool represents the

equipment shaft. It is critical that the reduced direction be found for proper ring

cutting. Rings that have been die-formed by the packing manufacturer are size on

size.

Example: 3/8" Square

Cross-Section

Cut t ing Rings

Packing rings can be cut with either a straight (butt cut) or diagonal (angle cut) joint. Straight cuts are used inservices less than 1,000 psi, diagonal cuts are recommended in services over 1,000 psi. Most die-formed

pre-cut rings will have a diagonal cut since the diagonal cut will perform in both high and low pressures. Thepurpose of the diagonal cut is to allow a surface that the pressure can act on to close the joint. The angle

must be cut by a "top view" of the ring rather than a "face view". A diagonal cut by a "face view" will performno better than a straight cut in service. Some materials, even on higher pressure applications should bestraight cut, as some packing materials may fray with an angle cut. Consult the packing manufacturer

concerning those particular materials.

.350

.375

3/8

(.375)

Straight Cut (

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