4. 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
BASIC UNDERSTANDING
5. 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
Flange
Cups or Containers
Tie rods
Purge
inlet
Cooling Design example
Flange bolts
and nuts
Piston rod
BASIC UNDERSTANDING
6. 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
BASIC UNDERSTANDING
7. • Seal gas or oil
– in compression chamber
– in intermediate piece
• Maintain a positive seal
at the piston rod even though there is
lateral movement of the rod
e
n
d
c
l
e
a
r
a
n
c
e
Function of Pressure Packings
axial clearance
piston rod
piston rod
radial
clearance
lateral
axial
BASIC UNDERSTANDING
8. • The rings segments are held together by garter springs until
the 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 between
the ring segments of one ring are covered by the ring segments
of the other to reduce leakage.
• Rings can float axially and radially in the grooves of the cups
to compensate for rod movement.
Function of Pressure Packings
piston rod
garter springs
seal rings
BASIC UNDERSTANDING
9. Sealing System for Piston Rods of Compressors
Segmented
rings
Housing
Piston rod
Garter springs
Radial cut ring Tangential
cut ring
BASIC UNDERSTANDING
10. Sealing System for Piston Rods of Compressors
Segmented
rings
Housing
Piston rod
Garter
springs
Gas pressure loads
the ring segments,
forcing them onto the rod
and against the housing
crank end
cylinder end
BASIC UNDERSTANDING
11. Sealing System for Piston Rods of Compressors
When the packing is not
pressurized by gas, the
garter springs hold the
ring segments in place
around the piston rod.
BASIC UNDERSTANDING
12. Axial and radial
clearance allow the
rings to float in the
housing , thus leakage
is prevented by always
maintaining a positive seal.
Sealing System for Piston Rods of Compressors
If lip seals were used
they would not conform
to the rod as it would
not compensate for
the rod movement. For
this reason segmental
rings are used.
BASIC UNDERSTANDING
13. Gaps of one ring
are covered
by the face
of the other ring.
Rings are positioned by a pin
Sealing System for Piston Rods of Compressors
BASIC UNDERSTANDING
14. Sealing System for Piston Rods of Compressors
End clearance
between ring
segments allows
worn rings to
compensate for
wear automatically.
Tangential cut
rings act like
a camera lens.
BASIC UNDERSTANDING
15. Gaps of one ring
are covered
by the face
of the other ring.
Rings are positioned by a pin
Axial and radial
clearance allow the
rings 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 the
ring segments in place
around the piston rod.
Gas pressure loads
the ring segments,
forcing them on to
the rod and housing
Sealing System for Piston Rods of Compressors
If lip seals were used
they would not conform
to 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.
BASIC UNDERSTANDING
16. Sealing System for Piston Rods of Compressors
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
pressure
pressure profile
BASIC UNDERSTANDING
17. 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 material
gas condition
• Lube - ring material, number of lube points
• Rod material - ring material
• Rod surface - ring material
• Customer’s demand - materials and design
• Expected life time - material, design
• Costs - design and material
BASIC UNDERSTANDING
18. 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
BASIC UNDERSTANDING
19. Components of Pressure Packings
Flange
Flange Plates
Plates
Soft metal gasket
(joint) to seal
on stuffing box
Soft metal gasket
(joint) to seal
on stuffing box
Sealing Ring Sets
Sealing Ring Sets
Containers (Cups)
Containers (Cups)
etc.
etc. etc.
O-Rings
O-Rings
etc.
Crank end Cylinder end
BASIC UNDERSTANDING
20. Contents
• Function
• Single Acting Ring Groups
• Double Acting Ring Groups
• Side Loaded Ring Groups
• Special Rings
• Pressure Breakers
• Clearance figures
RING THEORY
21. 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 and
the rod smaller than the gap between the housing and the rod
• Ring set: consists of several rings
RING THEORY
22. Function of a Single Acting Ring Pair
Side clearance in the cups
and radial cut ring gaps
avoid gas traps.
They allow the gas inside
the cups to return
to the cylinder.
Gas enters the cup via the
side clearance in the cups
and gaps in radial cut ring
and loads tangent cut ring
onto piston rod.
Tangent cut ring
gaps are sealed
by radial cut ring
Cylinder end Crank end
Cylinder end Crank end
Axial movement
of piston rod
Axial movement
of piston rod
Axial movement
of piston rod
Axial movement
of piston rod
tangential ring
radial ring
RING THEORY
23. Single Acting Ring Group Type 0342
Description: Rings located relative to each by a peg in tangential cut
ring mating hole in radial cut ring. By this gaps of
tangential cut rings are covered by radial cut ring.
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.
Rings
without gap
are worn out
and must be
exchanged.
Tangential cut ring
Radial cut ring
Pressure
ring
type
0306
ring
type
0304
gap
gap
RING THEORY
24. Description: Radial cut ring 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 brittle ring materials , for pressures above 150 bar
with metal Bridge Pieces
Single Acting Ring Group Type 0353
Pressure
6-piece tangential cut ring
Radial cut ring
ring
type
0322
ring
type
0304
RING THEORY
25. 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 ring
Radial cut
seal ring
Single Acting Ring Group Type 0371
Pressure
Tangential cut
seal ring
ring
type
0310
ring
type
0304
ring
type
0306
Bronze, Peek, PPS
Bronze, Peek, PPS
RING THEORY
26. Function of a Double Acting Ring Group
Gaps in both
tangent cut rings
sealed because
rings are pegged
to prevent gaps
aligning.
Gas enters the cup
via side clearance and
loads tangent cut rings
onto piston rod.
Cylinder end Crank end
On reverse stroke gas
is sealed in the same
manner as described
for the crank stroke.
Cylinder end Crank end
Gas is trapped
in the container.
Axial movement
of piston rod
Axial movement
of piston rod
Axial movement
of piston rod
Axial movement
of piston rod
RING THEORY
27. 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.
Double Acting Ring Group Type 0344
ring
type
0306
ring
type
0308
Pressure
RING THEORY
28. Description: Double acting ring set with backup ring
Application: Standard set for pressures of less than 12 bar
and higher temperatures
Double Acting Ring Group Type 0372
Tangential cut
seal ring
Tangential cut
seal ring
Backup ring or
anti-extrusion ring
Pressure
ring
type
0310
ring
type
0306
ring
type
0308
RING THEORY
29. Description: Double acting ring pair consisting of two 4-segment
radial cut rings 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 brittle materials
Disadvantage: no wear limit, difficult to install
Double Acting Ring Group Type 0347
Cut lines do not meet the centre !
ring
type
0317
ring
type
0316
Pressure
RING THEORY
30. Description: always maintains a seal between tangential cut and
container sealing face due to the inclined nature of the
faces of the 2 radial cut rings and garter spring load.
Application: Main Packings at low pressure side near vent and purge,
also in Intermediate (Partition) Packings and
Oil Tight Packings.
Side Loaded Pressure Ring Group Type 0373
Radial cut ring with
chamfered recess
Radial cut ring with
chamfered boss
Tangential cut
ring with peg
Pressure
ring
type
0314
ring
type
0313
ring
type
0312
Pressure
RING THEORY
31. 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 restriction; possibility of damage to inboard
feather edges if rod is inserted into assembled packing.
Special Rings Type 0309 and 0328
Single acting
tangential cut ring
without wear restriction
Double acting
tangential cut ring
without wear restriction
ring
type
0309
ring
type
0328
Pressure Pressure
RING THEORY
32. Single acting ring
with relief slots in the middle of
segments and chamfers on joint
Description: Reduce pressure and throttle gas pressure pulsations
but not to seal.
Application: Pressures greater then 20 bar,
used on their own filling a recess,
or with backup ring when non metallics (PTFE).
Pressure Breaker Rings 0301 and 1302
Double acting
ring
ring
type
1302
ring
type
0301
Pressure Pressure
RING THEORY
33. Nomenclature of HRP Rings
Ring
radial
thickness
Recess
dia
Container
(cup)
outer
dia Recess
depth
Container (cup)
thickness
Ring
axial width
Dimensions of standard rings
are according to HRP standard TDSM 115
RING THEORY
34. Pressure and Intermediate Packings
Flanges
Flanges
Containers
Containers
• Flanges, Containers (cups), Plates
Types - Function - Clearance - Surface Quality - Materials
• Other Parts
Tie rods - O-rings - Static Sealing
HOUSING THEORY
35. Types of Flanges and Containers
Flanges
Flanges
T-Container (cup) L-Container (cup) Plate
• vented
• plain
• cooled
• lube
• vented
• plain
• for purge
Spigotted Flange
HRP Standard
Recessed Flange
cannot be lapped
Containers (cups) Containers (cups)
Containers
Containers
HOUSING THEORY
36. Functions of Flanges and Containers
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 reduction
of containers after reconditioning (by
installing a thicker plate).
Dimensions: Dimensions of flanges, containers, plates
are according to HRP standard TDSM 182
HOUSING THEORY
37. FLANGES
Spigot 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
Clearance and Surface Quality
DETAILS - HOUSING THEORY
38. Standard : Grey iron BS1452 GR.250
Carbon steel BS970 GR 070M55
Stainless steel BS970 GR 316S16
Specials : As required by customers
Materials
Refer to TDSM213 for application details via HRP Intranet
DETAILS - HOUSING THEORY
39. Details: O-Rings - Static Sealing
High material and surface quality
Captive rectangular
section gasket (joint)
from copper or soft iron
O-ring material according to customer’s order
Tie rod
OTHER COMPONENTS
40. Details: Static Sealing Function
The joint 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 the
stuffing box with no contamination.
This is as important a seal
as any of the sealing rings.
OTHER COMPONENTS
41. • Calculation of Leakage Rates by HRP
• Leakage Control System ECM
LEAKAGE
42. Calculation of Leakage Rates to HRP Standards
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.
LEAKAGE
43. Vent and Purge Arrangement
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 possible
leakage 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 side
Nitrogen IN
Piped controlled leakage
to dangerous gas/nitrogen vent Lubrication (on top)
Nitrogen
Oil drain
Nitrogen Dangerous
gas
to distance
piece vent
LEAKAGE
44. Vent and Purge System, Pressures, Leakage flows to API 618
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 restriction from vent / flare line system.
If the vent line back pressure and restriction 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 fitted with SLP rings and AL (5 ring) sets).
Recycling Vent Flows - to suction system of the compressor
If the first stage suction 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 fitted with an intermediate HP vent
connection as well as a low pressure vent connection for even break-
down of pressure across all rings.
LEAKAGE
45. 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 differential
pressure of the purge to vent gas.
If gas flow to flare exceeds a limiting
value an alarm is switched on.
Emission Control and Monitoring System ECM
• Modular construction,
up to 4 cylinders per cabinet
• Satisfies emissions legislation
to API618 & NACE
• Optional flow controlled purge
for valve unloaders, intermediate &
wiper packings
LEAKAGE
46. F1: Flowmeter (metallic type)
Flow range 10 – 30 l/min
F2: Flowmeter (rotameter)
Flow range 0 – 10 l/min
Purge Panel Diagram of the ECM
Vent pressure
Vent flow
F1
VENT
OUTLET
TO FLARE
NITROGEN
PURGE TO
PACKING
Purge flow
G3
F2 V4
G1
V5
Purge pressure
V3
Purge Compensation
Regulator, adjustable
Gauge
Regulator
Shut Off
NITROGEN
SUPPLY
max. 16 bar
typ. 10 bar
V2
V1
PURGED GASSES
FROM PACKING
max pressure 16 bar
YYP range 1 – 3 bar
G2
LEAKAGE
47. • HRP Cooling System
• HRP Drilled Radial Flow Type
Design of cooled packings is currently under review
COOLING OF PRESSURE PACKINGS
48. HRP Cooling System
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.
COOLING OF PRESSURE PACKINGS
49. HRP Cooling System
Forced flow cooling by 340° milled groove gives:
– improved water flow
– no stagnancy
– reduced pressure drop through packing cooling system
water
water
outlet
cooling
water
inlet
water
water
outlet
water
inlet
Required cooling water:
pressure : 0.5 to 5 bar
max. temperature: 40°C
COOLING OF PRESSURE PACKINGS
50. HRP Drilled Radial Flow Type- conforms to API 618
• Better coolant flow
with reduced losses
• Meets API 618 revision 4
by eliminating “O” rings
which surround the piston
rod
• Easier to change
packing rings
without removing
the piston rod
• Cooling passages
can be cleaned
by removal of plugs
COOLING OF PRESSURE PACKINGS
51. • Main Characteristics
• Typical Pressure Packing Types
• HRP Stationary Gas Seal
• Features of HRP Pressure Packings
• Testing of Pressure Packings
PRESSURE PACKING TYPES
52. Characteristics
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”.
PRESSURE PACKING TYPES
53. Non lube, uncooled, not vented, not purged,
for discharge pressures less than 10 bar
Double acting ring
groups are used
0308
0306
RING GROUP 0344
Crank
end
Cylinder
end
TYPICAL PACKING TYPES
54. Non lube, uncooled, not vented, not purged,
RING GROUP 0371
0310
0304 0306
Crank
end
Cylinder
end
for discharge pressures less than 30 bar
Pressure Breaker Ring Single acting ring groups
RING GROUP 0349
0310
1302
TYPICAL PACKING TYPES
55. Lube
Lube, uncooled, not vented, not purged,
for discharge pressure from 30 bar to 70 bar
Crank
end
Cylinder
end
oil
oil
from cylinder
lube pump
RING GROUP 0371
0310
0304 0306
Pressure Single acting
Breaker Ring ring groups
RING GROUP 0349
0310
1302
TYPICAL PACKING TYPES
56. Non lube, cooled, not vented, not purged - 170 bar
Crank
end
Cylinder
end
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
TYPICAL PACKING TYPES
57. Non lube, uncooled, vented, not purged - 70 bar
Vented gas is piped to flare or
to a lower pressure level of compressor.
Gas vent
SLP ring group:
side load pressurized,
behind vent
For dangerous gases - toxic or explosive:
For dangerous gases - toxic or explosive:
Crank
end
Cylinder
end
RING GROUP 0373
0312
0314 0313
TYPICAL PACKING TYPES
58. Non lube, uncooled, vented and purged - 70 bar
For very dangerous gases or low emission values
For very dangerous gases or low emission values
purge
gas
purge
gas
gas
mixture
Crank
end
Cylinder
end
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
TYPICAL PACKING TYPES
59. HRP Design
Segmental Packing Rings
only seal during dynamic reciprocating action.
Piston energised
Piston energised
DYNAMIC : NO ROD CONTACT
STATIC : ROD CONTACT
Pneumatically
operated
externally,
when the rod
is stationary
to prevent
cylinder gas
emission
Cylinder
end
Stationary Gas Seal energises when the compressor is stopped
Stationary Gas Seal energises when the compressor is stopped
STATIONARY GAS SEAL
60. Segmental packing rings only seal
during dynamic reciprocating action.
Distance
piece
Cylinder
end HRP Design
Cartridge unit fitted to existing
Packing increasing length
For standstill additional parts are necessary
STATIONARY GAS SEAL
61. Application Features
TYPICAL WATER COOLED PRESSURE PACKING
Face & outside dia connections
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 rod
drop indicator
to detect
rider ring
wear
FEATURES OF HRP PRESSURE PACKINGS
62. Design Features
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
`O'-Ring design can be captive, totally eliminating
possibility of gas leakage into water channels
Fully lapped faces with O-Rings
eliminate static leakage
TYPICAL WATER COOLED PRESSURE PACKING
FEATURES OF HRP PRESSURE PACKINGS
63. Standard and Extra Leakage Testing Procedures
Standard test of water cooled packings:
• 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
TESTING OF HRP PRESSURE PACKINGS
