1 - Pressure Packing

8/13/2019 1 - Pressure Packing

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Main Pressure Packing Intermediate Packing


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Contents

Basic Understanding Ring Theory Housing Theory

Leakage Control

Cooling Systems for Packings Typical Packing Types Associated Products - Piston Rods

Main Pressure Packing Intermediate Packing


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Basic Understanding

Task and Types

Function Sealing System Design


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Task and Types of Pressure Packings

Task : Create a positive seal at the piston rod

Types : Main Pressure Packing - Intermediate Packing

Double

Distance

Piece

Double

Acting

Cylinder

Crosshead Crankcase


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Seals the inboard compression chamber to distance piece

in the area of the piston rod. Can be lube or non lube.

Pressure range from vacuum to 3000 bar.

Main Pressure Packing

Ring sets

O-Rings

FlangeCups or Containers

Tie rods

Purge

inlet

Cooling Design example

Flange bolts

and nuts

Piston rod


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Intermediate Packings seal the first distance piece

to the second distance piece in the area of the piston rod.

Usually they are not lubricated and not water cooled.

Intermediate Packing

Flange

Cups or

Containers

Ring sets

Tie rods

Purge (plugged)

Flange bolts

and nuts

Design example

Piston rod


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Seal gas or oil

in compression chamber in intermediate piece

Maintain a positive seal

at the piston rod even though there islateral movement of the rod

end

clearance

Function of Pressure Packings

axial clearance

piston rodpiston rod

radial

clearance

lateral

axial


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The rings segments are held together by garter springs untilthe gas pressure is such that they are forced on to the rod

to create the seal.

Sealing rings are pegged together so that the gaps betweenthe ring segments of one ring are covered by the ring segmentsof the other to reduce leakage.

Rings can float axially and radially in the grooves of the cupsto compensate for rod movement.

Function of Pressure Packings

piston rod

garter springs

seal rings


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Sealing System for Piston Rods of Compressors

Segmented

rings

Housing

Piston rod

Garter springs

Radial cut ring Tangential

cut ring


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Segmented

rings

Housing

Piston rod

Garter

springs

Gas pressure loads

the ring segments,

forcing them onto the rod

and against the housing

crank endcylinder end


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Sealing System for Piston Rods of CompressorsWhen the packing is not

pressurized by gas, the

garter springs hold thering segments in place

around the piston rod.


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Axial and radial

clearance allow the

rings to float in the

housing , thus leakage

is prevented by always

maintaining a positive seal.


If lip seals were used

they would not conformto the rod as it would

not compensate for

the rod movement. For

this reason segmental

rings are used.


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Gaps of one ring

are covered

by the face

of the other ring.

Rings are positioned by a pin



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End clearance

between ring

segments allows

worn rings to

compensate forwear automatically.

Tangential cut

rings act like

a camera lens.

S li S f Pi R d f C


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Gaps of one ringare covered

by the face

of the other ring.

Rings are positioned by a pin

Axial and radial

clearance allow therings to float in the

housing , thus leakage

is prevented by always

maintaining a positive seal.

When the packing is not

pressurized by gas, the

garter springs hold thering segments in place

around the piston rod.

Gas pressure loads

the ring segments,

forcing them on to

the rod and housing


If lip seals were used

they would not conformto the rod as it would

not compensate for

the rod movement. For

this reason segmental

rings are used.

End clearance

between ring

segments allows

worn rings to

compensate for

wear automatically.

Tangential cut

rings act like

a camera lens.



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Stepwise pressure reduction by each packing ring group:

Rule of the thumb for packings:

Each recess of a new packing will reduce the pressure by half. If one ring

pair is worn, the pressure has to be reduced by the remaining ring pairs.

The pressure profile will differ then from the pictured profile.

The last sealing

ring group is

responsible for

the leakage to

the outside.

packing

ring groups

atmospheric

pressure

pressure

p

packing assembly

Piston

rod

Piston

rod

leakage

discharge

pressurepressure prof ile

Design Criteria


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Design Criteria

Differential pressure - Number of ringsets,with or without cooling

Temperature - Cooling, ring material

Speed of the rod - Cooling , ring material

Gas type and - Vent, ring type,ring materialgas condition

Lube - ring material, number of lube points

Rod material - ring material

Rod surface - ring material

Customers demand - materials and design

Expected life time - material, design

Costs - design and material

Number of Ring Groups of Main Pressure Packings


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Number of Ring Groups of Main Pressure Packings

Pressure range of HRP filled TFE packings for compressors

pressure

(bar)

uncooled

not vented 4 sets 5 sets 6 sets 7 sets

(Air)

uncooled

vented 5 sets 6 sets 7 sets 8 sets

(Gas)

cooled

not vented 4 sets 5 sets 6 sets 7 sets 8 sets 9 sets

(Air)

cooled

vented 5 sets 6 sets 7 sets 8 sets 9 sets 10 sets

(Gas)

All packings above

70 bar whether

vented or unvented

must be cooled and

should be lubricated.

0 - 12 12.5 - 21 21.5 - 35 35.5 - 70 70.5 - 316 316.5 up

1 lube point 2 lube points

Components of Pressure Packings


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Components of Pressure Packings

FlangeFlange PlatesPlates

Soft metal gasket

(joint) to seal

on stuffing box

Soft metal gasket

(joint) to seal

on stuffing boxSealing Ring SetsSealing Ring Sets

Containers (Cups)Containers (Cups)

etc.

etc. etc.

O-RingsO-Rings

etc.

Crank end Cylinder end

Contents


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Contents

Function Single Acting Ring Groups Double Acting Ring Groups

Side Loaded Ring Groups

Special Rings Pressure Breakers Clearance figures

Function


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Function

Classification of rings according to their functions:

Seal ring

Pressure breaker reduces the pressure by throttling the gas flow

Anti-extrusion ring - usually called backup ring

for pressures higher than approx. 15 bar

made out of stronger material than the seal rings

located on low pressure side, with a gap between the ring andthe rod smaller than the gap between the housing and the rod

Ring set: consists of several rings

Function of a Single Acting Ring Pair


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Function of a Single Acting Ring Pair

Side clearance in the cups

and radial cut ring gaps

avoid gas traps.

They allow the gas insidethe cups to return

to the cylinder.

Gas enters the cup via the

side clearance in the cupsand gaps in radial cut ring

and loads tangent cut ring

onto piston rod.

Tangent cut ringgaps are sealed

by radial cut ring

Cylinder end Crank end


Axial movement

of piston rod

Axial movement

of piston rod

Axial movementof piston rod


tangential ringradial ring

Single Acting Ring Group Type 0342


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Description: Rings located relative to each by a peg in tangential cut

ring mating hole in radial cut ring. By this gaps oftangential cut rings are covered by radial cut r ing.

Task: Seals only, when the crank end of the cylinder is

compressing gas

Application: Standard ring set for low to medium pressures

Wear limit:

Gaps decrease

to zero when

ring wears.

Ringswithout gap

are worn out

and must be

exchanged.

Tangential cut ringRadial cut ring

Pressure

ring

type

0306

ring

type

0304gap g

ap



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Description: Radial cut r ing combined with 6 piece design, instead of

3-piece design tangential cut ring.Task: Tangential cut is continued across the segment creating

Bridge Pieces

Application: for brit tle ring materials , for pressures above 150 bar

with metal Bridge Pieces

g g g p yp

Pressure

6-piece tangential cut r ingRadial cut ring

ring

type

0322

ring

type

0304



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Description: Single acting standard ring pair with backup ring.

Backup ring is bored to have 0.1 to 0.2 mm clearance

on the piston rod and hence no gaps when fitted.

Application: Standard ring group for pressures above 21 bar

Backup or

anti-extrusion ringRadial cut

seal ring

g g g p yp

Pressure

Tangential cutseal r ing

ring

type

0310

ring

type

0304

ring

type

0306

Bronze, Peek, PPSBronze, Peek, PPS

Function of a Double Acting Ring Group


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g g p

Gaps in both

tangent cut ringssealed because

rings are pegged

to prevent gaps

aligning.

Gas enters the cup

via side clearance andloads tangent cut rings

onto piston rod.


On reverse stroke gas

is sealed in the same

manner as described

for the crank stroke.


Gas is trapped

in the container.

Axial movement

of piston rod

Axial movement

of piston rod



Double Acting Ring Group Type 0344


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Description: 2 tangential cut rings pegged together in such a way

that the segments of one ring mask the end gaps of

the other ring.Task: Seal in both strokes of the compression cycle.

Application: Low pressures or vacuum, Intermediate Packing,

pulsation seal in Wiper Packings, final or vent seal

in Main Pressure Packings.

g g p yp

ring

type

0306

ring

type

0308

Pressure



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Description: Double acting ring set with backup r ing

Application: Standard set for pressures of less than 12 bar

and higher temperatures

oub e c g g G oup ype 03

Tangential cutseal ring

Tangential cutseal ring

Backup ring oranti-extrusion ring

Pressure

ring

type

0310

ring

type

0306

ring

type

0308



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Description: Double acting ring pair consisting of two 4-segment

radial cut r ings pegged together, so that the segments

of one ring masks the end gaps of the other.

Application: Where brittle materials must be used, e.g. carbon

Advantage: sturdy parts, frequently used with bri ttle materials

Disadvantage: no wear limit , difficult to install

g g p yp

Cut lines do not meet the centre !

ring

type

0317

ring

type0316

Pressure

Side Loaded Pressure Ring Group Type 0373


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Description: always maintains a seal between tangential cut and

container sealing face due to the incl ined nature of thefaces of the 2 radial cut rings and garter spring load.

Application: Main Packings at low pressure side near vent and purge,

also in Intermediate (Partit ion) Packings and

Oil Tight Packings.

Radial cut ring with

chamfered recess

Radial cut ring with

chamfered boss

Tangential cut

ring with peg

Pressurering

type

0314

ring

type

0313

ring

type

0312

Pressure

Special Rings Type 0309 and 0328


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Description: No direct leakage path beween the segments,needs no further ring for proper sealing.

Application: Where small containers must be installed.

Disadvantage: No wear restrict ion; possibil ity of damage to inboard

feather edges if rod is inserted into assembled packing.

Single acting

tangential cut r ing

without wear restriction

Double acting

tangential cut ring

without wear restriction

ring

type

0309

ring

type

0328

Pressure Pressure

Pressure Breaker Rings 0301 and 1302


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Single acting ring

with relief slots in the middle of

segments and chamfers on joint

Description: Reduce pressure and throttle gas pressure pulsationsbut not to seal.

Application: Pressures greater then 20 bar,

used on their own fill ing a recess,

or with backup ring when non metallics (PTFE).

g

Double acting

ring

ring

type

1302

ring

type

0301

Pressure Pressure

Nomenclature of HRP Rings


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Ring

radialthicknes

s

Recessd

ia

Container(cup)

outerdia

Recess

depth

Container (cup)

thickness

Ringaxial width

Dimensions of standard rings

are according to HRP standard TDSM 115

Pressure and Intermediate Packings


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g

FlangesFlanges

ContainersContainers

Flanges, Containers (cups), PlatesTypes - Function - Clearance - Surface Quality - Materials

Other PartsTie rods - O-rings - Static Sealing

Types of Flanges and Containers


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FlangesFlanges

T-Container (cup) L-Container (cup) Plate

vented plaincooled

lube vented plain

for purge

Spigotted FlangeHRP Standard

Recessed Flangecannot be lapped

Containers (cups) Containers (cups)

ContainersContainers

Functions of Flanges and Containers


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Flange : Contains the connections for lube oil,

cooling water, vent and purge.Containers are fixed with tie rods to flange.

Container : Contains the ring sets and the holes

(cup) for lube oil, cooling water, and vent.

Plate : Contains the holes for vent.

Masks the milled cooling water grooves.

Compensates the thickness reductionof containers after reconditioning (by

installing a thicker plate).

Dimensions: Dimensions of flanges, containers, plates

are according to HRP standard TDSM 182

Clearance and Surface Quality


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FLANGESSpigot dia : Spigot dia. as Container (cup) outer diameter

Recess dia : Recess dia = Stuffing box nom. bore +0 to 0.15 mm

As recesses cannot be lapped effectively,

recessed type flanges should be avoided.

SEALING FACES on Containers, Flanges and Plates

Surface finish low pressure: < 70 bar high pressure: > 70 bar

and Flatness : uncooled Packings low MOL weight or

cooled Packings

0.4& 0.002

0.2& 0.001

or

Materials


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Standard : Grey iron BS1452 GR.250

Carbon steel BS970 GR 070M55

Stainless steel BS970 GR 316S16

Specials : As required by customers

Refer to TDSM213 for application details via HRP Intranet

Details: O-Rings - Static Sealing


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High material and surface quali ty

Captive rectangular

section gasket (joint)

from copper or soft iron

O-ring material according to customers order

Tie rod

Details: Static Sealing Function


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Thejoint forms the only static seal

as part of the main pressure packing,

which seals against the bottom of

the stuffing box in the compressor.

It is important that the static seal is

flat and parallel.

It is also important that there is a

good surface at the bottom of thestuffing box with no contamination.

This is as important a seal

as any of the sealing rings.


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Calculation of Leakage Rates to HRP Standards

It is difficult to define exactly how much gas will leak through a pressure


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It is difficult to define exactly how much gas will leak through a pressure

packing. A slight leakage is fundamental to the operation of the packing.

Major factors influencing leakage are the discharge pressure of the compressor, the size of the piston rod

the molecular weight of the gas any lubrication.

Secondary factors include surface finish of the rod and the containers,

gas contamination and machine misalignments.

Compressors can suffer higher than normal leakage if operated at very low pressures, if running at partial or off-load, if (new) packings have not bedded in.

Vent and Purge ArrangementFor dangerous gases or low emission values the containers near to the


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For dangerous gases or low emission values the containers near to the

distance piece of Pressure and Intermediate Packing are purged.

A flow of Nitrogen purge gas is inlet into the packing to stop possibleleakage of dangerous gas into the crank case and further on into the

compressor room. It could also contaminate oil and lower its flash point.

Crankcase side Cylinder sideNitrogen IN

Piped controlled leakage

to dangerous gas/nitrogen vent Lubrication (on top)

Nitrogen

Oil drain

Nitrogen Dangerous

gas

to distancepiece vent

Vent and Purge System, Pressures, Leakage flows to API 618

Vent Pressure up to1 5 barg maximum to API 618 Appendix 1


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Vent Pressure - up to1.5 barg maximum to API 618, Appendix 1

depends on both the leakage flow escaping past the packing rings and

the back pressure and flow restrict ion from vent / flare line system.If the vent line back pressure and restrict ion remains constant, then an

increasing vent line pressure indicates increasing packaging leakage.

Purge gas pressure - up to 2.5 barg.

should be at least 1 bar above the Vent Pressure

Purge Gas Flow (Leakage) Rates

< 1 to 6 l /min for packing with rod and containers in good condition

and new bedded-in wear parts with back to back SLP (WAT) rings.

(Valid for purge systems fi tted with SLP rings and AL (5 ring) sets).

Recycling Vent Flows - to suction system of the compressor

If the first stage suct ion pressure is < 1.5 barg, any leakage may be

recycled to reduce the overall leakage (depending on installation).

Intermediate Vent Connections - at higher pressures

High pressure packings may be fit ted with an intermediate HP vent

connection as well as a low pressure vent connection for even break-

down of pressure across all rings.

Emission Control and Monitoring System ECM


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Purge pressure and purge flow are

controlled, consumption of purge gas

(N2) is minimized.

The equipment adjusts purge gas inlet

pressure to compensate for increase in

vent pressure and keeps the differentialpressure of the purge to vent gas.

If gas flow to flare exceeds a limiting

value an alarm is switched on.

Modular construction,up to 4 cylinders per cabinet

Satisfies emissions legislationto API618 & NACE

Optional flow controlled purgefor valve unloaders, intermediate &

wiper packings

Purge Panel Diagram of the ECM


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F1: Flowmeter (metallic type)Flow range 10 30 l/min

F2: Flowmeter (rotameter)

Flow range 0 10 l/min

Vent pressure

Vent flow

F1

VENT

OUTLET

TO FLARE

NITROGEN

PURGE TO

PACKING

Purge flowG3

F2 V4

G1

V5

Purge pressure

V3

Purge Compensation

Regulator, adjustable

GaugeRegulatorShut Off

NITROGEN

SUPPLY

max. 16 bartyp. 10 bar

V2

V1

PURGED GASSES

FROM PACKINGmax pressure 16 bar

YYP range 1 3 bar

G2


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HRP Cooling System

HRP Drilled Radial Flow Type

Design of cooled packings is currently under review

HRP Cooling System

Frictional heat has to be dissipated


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Frictional heat has to be dissipated.

For discharge pressures greater than 70 bar

water cooling is necessary in general.

For lower pressures water

cooling is necessary

only under special conditions.

HRP Cooling System


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Forced flow cooling by 340 milled groove gives:

improved water flow no stagnancy

reduced pressure drop through packing cooling system

waterwateroutlet

cooling

water

inlet

waterwater

outlet

water

inlet

Required cooling water:

pressure : 0.5 to 5 bar

max. temperature: 40C

HRP Drilled Radial Flow Type- conforms to API 618


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Better coolant flowwith reduced losses

Meets API 618 revision 4by eliminating O rings

which surround the pistonrod

Easier to change

packing ringswithout removing

the piston rod

Cooling passagescan be cleaned

by removal of plugs


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Main Characteristics Typical Pressure Packing Types HRP Stationary Gas Seal

Features of HRP Pressure Packings Testing of Pressure Packings

Characteristics

Th i h t i ti f P P ki


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The main characteristics of Pressure Packings are:

lube or non-lube with or without cooling with or without vent

with vent and with or without purge

These characteristics are dependent upon:

discharge pressure differential temperature. piston speed

customer specification

process requirements

Type and number of ring groups depend on the design criteria

see Basic Understanding.

Non lube, uncooled, not vented, not purged,for discharge pressures less than 10 bar


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Double acting ring

groups are used

03080306

RING GROUP 0344

C

rankend

Cy

linderend

Non lube, uncooled, not vented, not purged,

for discharge pressures less than 30 bar


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RING GROUP 0371

03100304 0306

C

rankend

Cylinderend

Pressure Breaker Ring Single acting ring groups

RING GROUP 0349

03101302

LubeLube, uncooled, not vented, not purged,

for discharge pressure from 30 bar to 70 bar


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C

rankend

Cy

linderend

oiloilfrom cylinder

lube pump

RING GROUP 0371

03100304 0306

Pressure Single actingBreaker Ring ring groups

RING GROUP 0349

03101302

Non lube, cooled, not vented, not purged - 170 bar

F t th 70 b


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C

rankend

Cy

linderend

For pressures greater than 70 bar

cooled packings are recommended

O-rings are used to prevent the process gas

from entering the water channels and to also

prevent water from leaving the water channels

Non lube, uncooled, vented, not purged - 70 bar

For dangerous gases - toxic or explosive:For dangerous gases - toxic or explosive:


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Vented gas is piped to flare or

to a lower pressure level of compressor.

Gas vent

SLP ring group:

side load pressurized,

behind vent

g g pg g p

Crankend

Cylinderend

RING GROUP 0373

03120314 0313

Non lube, uncooled, vented and purged - 70 bar

For very dangerous gases or low emission valuesFor very dangerous gases or low emission values


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y g gy g g

purge

gas

purge

gas

gas

mixture

Cra

nkend

Cylin

derend

gas

Purge gas (mainly Nitrogen) is inlet in to

the last container. Inlet pressure normally

is 1 bar minimum above vent pressure.

The mixture of dangerous gas and purge

gas is piped to the vent collection

HRP Design

Segmental Packing Rings


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only seal during dynamic reciprocating action.

Piston energisedPiston energised

DYNAMIC : NO ROD CONTACT

STATIC : ROD CONTACT

Pneumatically

operatedexternally,

when the rod

is stationary

to preventcylinder gas

emissionCylinder

end

Stationary Gas Seal energises when the compressor is stoppedStationary Gas Seal energises when the compressor is stopped

HRP Design


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Segmental packing rings only seal

during dynamic reciprocating action.

Distance

piece

Cylinder

end

Cartridge unit fitted to existingPacking increasing length

For standstill addit ional parts are necessary

Application Features

Face & outside dia connections

k fl i bl


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TYPICAL WATER COOLED PRESSURE PACKING

make flange more serviceable.

Thermocouple to detect

increases in temperature

Detachable

flange to aid

assembly

Vent connection can be fitted with

an off-line flow measurement device

Facility for roddrop indicator

to detect

rider r ing

wear

Design Features`O'-Ring design can be captive, totally eliminating

possibili ty of gas leakage into water channels


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Spiral wound

Gasket,optional, to

reduce static

leakage

Tee shaped Cup complete with`SLP' Rings & purge

(API618) allows for sealing faces to be machine-lapped

Milled groove

Coolant Channels

to reduce pressure

drop to a minimum

p y g g

Fully lapped faces with O-Ringseliminate static leakage

TYPICAL WATER COOLED PRESSURE PACKING

Standard and Extra Leakage Testing Procedures

Standard test of water cooled packings:


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Pressurised air (6 bar) is connected to cooling water inlet. Air inlet valve will be closed. Pressure drop is checked at the closed volume

Standard bubble test

Pressurised air (6 bar) is connected to cooling water inlet. Packings are submerged in water, bubbles indicate leakage.

After test packings are disassembled, cleaned, dried and

reassembled.

Test do not show reasseambling errors.

Extra test when required - all packings Check of the gas tightness between the test flanges


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Piston Rods

Piston Rods

Surface Finish - hardened rods Ra : 0,2 - 0,4 mSurface FinishSurface Finish - hardened rods Ra : 0,2 - 0,4 m


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Lube air compressor - unhardened 30 HRC, cut threads

Process gas compr. - Induction hardened (occasionally nitrided)50 to 55 HRC, rolled threads

Coated rods - Thermal plasma sprayed,

mostly to 65 - 70 HRC

MaterialsMaterials

- coated rods Ra : 0,2 - 0,25 m

Coating - Chromium oxide

for reducing - Ceramics (Metco P130), produced

rod wear and/or with plasma gun method (HVOF)

reconditioning - Tungsten Carbide produced with plasma

gun (HVOF) or Detonation Gun method

- coated rods Ra : 0,2 - 0,25 m

Coating - Chromium oxide

for reducing - Ceramics (Metco P130), produced

rod wear and/or with plasma gun method (HVOF)

reconditioning - Tungsten Carbide produced with plasma

gun (HVOF) or Detonation Gun method

higher value of Rapreferred


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End

of the Training File

Pressure Packings

1 - Pressure Packing

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Transcript of 1 - Pressure Packing