Cylinder Ring
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HOERBIGER Compression TechnologyHOERBIGER Compression Technology
Cylinder Rings
General Understanding
Cylinder Rings
General Understanding
Cylinder rings
Piston rings : between Piston and cylinder liner,
seal the compression space
Rider rings : Carry the weight of the piston and
half of the rod but should not seal
Basic Understanding
Manufacturing of Rings at HRP
6.1.2
for differential pressures 0.1 to 400 bar
for piston diameters 20 to 1400 mm
made of metals cast iron, bronze
and non metallics filled PTFE, PEEK, PPS, Carbon
Cylinder
Rings
Cylinder Rings
Nomenclature of Dimensions
LinerLiner
PistonPiston
axial clearance
axial clearance
axialring width .
axial riderring width
width of rider
ring groovewidth of piston
ring groove
cylinder DIA
outer DIA
of piston
inner DIA of
piston ring
piston ring
groove DIA
rider ring
grooveDIA
inner DIA of
rider ring
running
clearance
rider ring
radial thickness
piston ring
radial thickness
6.6.1
18/04/2012 5
Cylinder Ring Design Selection – Main Factors
The main factors which influence the design selection are:
• Pressures -> number of rings, style, material
• Temperature -> material, type, ring sizes
• Gas, its mol weight and state (lube, wet, dry, bone dry) -> number of rings
material, style
• Cylinder, Piston and Rod design -> size, style
• The allowable dimensions for our components -> number of rings, size, style
• Required features (pin hole, pressure balancing or reliving) -> ring style
• Counterface of the cylinder / liner or piston rod -> material
Basic Understanding
Number of Rings According to Experience
6.2.6
Differential Pressure Recommended Number
bar gauge psig of PTFE-Rings per Piston
0 - 10 0 - 150 2
10 - 15 150 - 225 3
15 - 25 225 - 375 4
25 - 30 375 - 450 5
30 - 50 450 - 750 6
50 - 100 750 - 1500 7
100 - 200 1500 - 3000 8
200 - 320 3000 - 4725 9
320 - 400 4725 - 6000 10
Differential pressure for
single acting compressors : Outlet pressure minus atmospheric pressure
double acting compressors: Outlet pressure minus inlet pressure
18/04/2012 7
Cylinder Rings – Over Run IssueThe piston rings must not leave the sliding area
UCL = Piston ring stack length + piston stroke - 2 x over-run
Bearing surface
Ring stack length
Sliding area = uninterupted
cylinder length (UCL)
Over-run < 3 mm or
< 25 % of ring width
Detail:
8
Basic Understanding
Ring Styles
pressure
balanced
with
expander
without
expander
twin
ring
6.2.3
Cut
Ring Profiles
straight cut angle cut overlapped cut
or step cut
Basic Understanding
Increasing Sealing Ability
6.2.4
Cut Rings with expander
Twin Piston Ring
single acting:
Cut rings, pegged together.
Rings for low pressure
applications,large diameters
Sealing is improved
by springing the ring
to the liner.
Double Twin
Piston Ring:
The smaller ring
blocks the gap in
the L-shaped ring
in one direction
Double twin
piston rings
seal in both
directions.
6.2.5
Basic Understanding
Pressure Compensation
Piston ring designs for high pressure application:
without pressure balancing with pressure balancing
force profile torsionforce profile torsion
unbalanced
force
unbalanced
force
Piston rings without pressure balancing will wear quick at high
differential pressures due to high contact pressure between the piston
ring and the liner. Grooves and radial holes of pressure balanced rings
allow a controlled leakage to the outer ring diameter; thereby reducing
the unbalanced force and torsion moment promoting reduced wear.
11
Description:
Simplest ring with
rectangular section
and straight cut (gap).
• Ring will not spin,
therefore preferred on
soft aluminium piston
Application:
Standard piston ring.
Standard Piston Ring Types
Ring Type 0800
straight cut
6.3.1
12
Description:
Ring with rectangular section
and angle cut.
• Greater sealing efficiency created by longer leakage
path for gas due to angle cut.
• Ring gap will not form witness lines on the cylinder liner.
Application:
Standard piston ring for
non brittle materials.
Standard Piston Ring Types
Ring Type 0801
angle cut
6.3.2
13
Description:
Ring with rectangular
section and angle cut,
2 piece design.
Application:
For smaller ring diameters
and less flexible materials,
to mount without warming up.
Standard Piston Ring Types
Ring Type 0804
angle cut
6.3.3
14
Description:
Ring with rectangular section
and step cut, greater sealing
efficiency created by smaller
gaps, more expensive.
Application:
Piston ring for greater sealing
efficiency.
Not for brittle materials!
Standard Piston Ring Types
Ring Type 0808
step cut,
(overlapped gap)
6.3.4
15
Description:
Ring with rectangular section
and step cut, 3 piece design,
greater sealing efficiency
created by smaller gaps,
more expensive.
Application:
For smaller ring diameters
and less flexible materials,
(especially metallic rings,
e.g. Bronze).
Standard Piston Ring Types
Ring Type 0811
step cut
(overlapped gap)
6.3.5
16
Description:
Pressure balanced ring with
rectangular section and angle cut.
Less pressure load but approx.
the same cross sectional area.
Application:
For high differential pressure per
ring. Longer life than plain rings.
Standard Piston Ring Types
Pressure Balanced Ring Type 0803
6.3.6
angle cut
17
Description:
Pressure balanced ring with
rectangular section and angle
cut, 2-piece design.
Less pressure load but approx.
the same cross sectional area.
Application:
For high differential pressure
per ring, longer life than plain
rings. For non-flexible materials.
Standard Piston Ring Types
Pressure Balanced Ring Type 0805
6.3.7
angle cut
18
Description:
Twin ring consisting of an
L-ring and a rectangular ring
both straight cut and pegged
together so that the gap of the
rectangular ring is covered
by the L-ring.
rectangular ring
L-ring
Application:
The Twin Piston Ring is single
acting and only seals against
the small rectangular ring.
For light gases.
Standard Piston Ring Types
Twin Piston Ring Type 0820
6.3.8
L-ring rectangular ring
gap
gap
19
Description:
Double Twin Ring consisting
of a T-ring type 0816 and
2 rectangular rings all straight
cut and pegged together so
that the gaps of the rectangular
rings are covered by the T-ring.
rectangular rings
T-ring type 0816
Application:
Double Twin Rings seal
in both directions.
Standard Piston Ring Types
T-Section Double Twin Ring Type 0816
6.3.9
T-ring T-ring Rectangular ringsRectangular rings
20Basic UnderstandingBasic Understanding Ring TypesRing Types
6.4
Rider RingsRider Ringsfor Compressors
18/04/2012 21
Rider Rings - BasicsFunctions of Rider Ring is to:
• support the piston
• prevent it from contacting the liner.
The Rider Ring should not seal the gas ! • specific bearing load
• ring projection
• piston velocity
• liner surface quality
• liner cooling
• gas type
• gas condition
• bedding in procedure
Factors which influence
Rider Ring wear:
22
Task:– to prevent the piston from contacting the cylinder liner.
– the rider ring should not seal the gas.
Design Criteria:– bearing load
– piston and liner material
– hardness of the liner
– surface quality of the liner
– lube or non lube
– gas type
Specific load values:– lube 0,07 MPa
– non lube 0,035 MPa
Calculation of load:
=weight of the piston* + half the rod weight*OD of rider ring x width of all rider rings
Basic Understanding
Task - Calculation
width of rider ring
OD
6.4.1
* for V- and W-form compressors only the component of weight vertical to the liner
Basic Understanding
Axial Clearance
6.4.3
Correct design of axial clearance
is important for good operation
The ring moves backwards and
forwards in the piston groove
hitting both groove side faces
causing the ring and the groove
side faces to be damaged.
Ring is deformed so that it
bellows within the groove.
axial clearance is too great
axial clearance is too small
axial clearance