Fundamentals of Mechanical Seal

1
PEM 3 KNOWLEDGE SHARING PRESENTATION

• FUNDAMENTALS OF MECHANICAL SEAL
• Presented by
• Emmanuel Raphael Essen
• (MNIMechE, MNIM, ISMN)
• October,
  2014

2

• Tables of content.
• Historical development of a Mechanical seal
• What is Mechanical Seal
• Reason for using Mechanical seal
• Advantages of Using cartridge seal.
• Types of seals
• Essential elements of a mechanical seal
• Mechanical seal Components
• Essential requirements for proper operation of a
  mechanical seal
• The fluid in the pump and seal area, Leakage,
  Seal failures and Leakage Rate.
• Effective forces in a mechanical sealPower
  consumption of a liquid lubricated mechanical
  seal
• Seal Face Material
• Power Consumption
• Classification of Mechanical Seal
• Many factors need to be considered in the
  application of a mechanical seal
• Mechanical seal application limit
• Seal faces loading devices
• Flush arrangement
• Selecting a Mechanical seal

3
Historical Development of a Mechanical seal At
the beginning of the nineteenth century, many
endeavours were made to develop a replacement for
the conventional, braided packing used for piston
pumps and rotating shafts. A more reliable system
for different kinds of liquid-conveying rotating
machinery was desired. By the 1930s, the James
Walker Group came up with a mechanical shaft seal
for refrigeration compressors. At the same time,
the John Crane company invented the first
automotive mechanical shaft seal. In the early
1940s, the company developed and introduced the
patented elastomer bellows axial shaft seal,
today known as Type 1. After this breakthrough
in sealing technology, other types of mechanical
shaft seals were developed. With several types of
mechanical shaft seals, the John Crane company
adopted the tagline, The right seal for the
right application. Today, John Crane is still a
leading seal manufacturer along with Grundfos,
Burgmann, Flowserve, etc.
4
What is Mechanical Seal Mechanical seal is a
sealing device for any rotating equipment which
prevents the inner fluid from leaking through the
clearance between the rotating shaft and the
housing case. There are various types of
mechanical seals for each application and
operating condition of the equipment but in
principle, mechanical seal is a face type seal,
which performs sealing by two sealing faces
vertical to the shaft. Mechanical Seal
incorporates various components such as the
spring giving contact force and the packing which
eliminates intrusion of the fluid from the
outside. The seal face is an accurately flat
face, and so if it is worn, it does not cause the
leakage of the sealant as far as wear is within
the maximum allowable amount. Therefore it can
be used for a long time free of maintenance, and
is very effective and efficient in terms of
reliability and economy Mechanical seals are
used not only in pumps but also in other various
equipment such as mixers, agitators, compressors,
rotary unions, submersible motors, etc.

5

• Reasons for using Mechanical seal
• To minimize leakage
• To prevent toxic fluids escaping to atmosphere
• To reduce power loss.
• Advantages of Using cartridge seal.
• By using cartridge seals the following can be
  achieved
• Reduced skill base
• Increased Reliability
• Fits multiple types of pumps
• Reduced downtime
• Increased operating profits.
• Types of seals Static Seals Dynamic Seals
• STATIC SEALS Sealing takes place between two
  parts that dont move in relation to each other.
• Application - Pipe flanges ,vessel /Tower
  nozzles, pump casing joint. - Fan /Blower casing
  joint , Compressor casing joint. - Turbine casing
  joint, Heat exchanger joints

6
Types Gaskets , O-rings etc GASKET Packing
designed to go between two rigid parts in
stationary conditions May be in form of sheet ,
strip , bulk. Properties Impermeability, Ability
to flow into joints, Corrosion resistance DYNAMIC
SEALS Used for sealing fluid between parts that
move in relation with each other. Application
Centrifugal pump gland, valve gland , bearing
housing Turbine/compressor inter stage and end
sealing , Reciprocating compressors cylinder
sealing TYPES Gland packings, Mechanical
contact seals, Labyrinth seal, Oil seal, Oil film
seals
7
Essential elements
of a mechanical seal The basic design of the
Mechanical seal consists of the following
elements Flexibly mounted seal face, Rigidly
mounted seal face, Compression device and
Secondary seal

• Mechanical seal Components
• Rotary seal face
• Stationary seal face
• Springs
• Retainer
• Sealing /flushing media
• O-rings

8

• Essential Requirements for Proper
  Operation of a Mechanical Seal
• These are the essential requirements
• Seal faces must be flat and polished.
• Seal faces must be installed perpendicular to the
  shaft.
• Spring force must be sufficient to maintain
  contact of the faces

The Fluid in the Pump and Seal
Area Key Point The fluid contacts the seal faces
and other parts in wide open areas, in very small
gaps and at the exit of the seal faces. Pressure
and temperature of the fluid will depend on its
location and determine its respective state, i.e.
liquid, gaseous, solid or a mixture.

9
Leakage A few facts about the leakage (and
wear) behavior of contacting mechanical seals It
is essential for proper lubrication and wear of
the faces. Normal leak rates range between
immeasurably small to steady drips or temporary
to even small steams. Some seals leak some of the
time, some seals never leak (measurably), and
some leak all the time. Leakage patterns can be
constant, progressive or erratic in nature. It
can be in liquid, gaseous and/or solid state.
Successful contacting seals tend to have very
low wear rates and low leakage rates. Some forms
of contact is necessary for low leakage rates.
Non-contacting or full lift off seals
(hydrostatic or hydrodynamic tend to have
visible, sizeably larger leakage rates.
10

• The large majority of mechanical seals never wear
  out and are removed from service for some other
  reason.
• Seal failures
• Seal failure occur for a wide range of reasons.
  Type of seal failures
• Lubrication failures Dry running and poor
  lubrication
• Contamination failures Clogging, Hang-up,
  Particles deposits, Sticking and seizure.
• Chemical, physical degrading and wear Ageing and
  swollen rubber parts, Corrosion, wear, Explosive
  decompression
• Installation failures Shaft misalignment, seats
  not mounted perpendicular to the shaft, axially
  moving shaft and wrong assembly length.
• System failures The pressure in the seal
  chamber, the temperature around the shaft seal in
  the seal chamber, the pumped medium, the speed,
  the shaft seal dimensions.

11

• Leakage rate
• The leakage rate of a mechanical shaft seal
  depends of a number of factors such as
• Surface roughness of seal faces
• Flatness of seal faces
• Vibration and stability of pump
• Speed of rotation
• Temperature, Viscosity and Type of pumped medium
• Pump pressure
• Seal and pump assembly.
• .

12

• Effective forces in a Mechanical Seal
• These are the forces operating in mechanical
  seals
• Axial and radial forces
• Closing and opening forces
• Hydrostatic and hydrodynamic forces
• Seal Face Materials Few materials are suitable
  for seal faces. To keep leakage as low as
  possible, the seal gap must be very small. As a
  result, the lubricating film is very thin.
• Consequently, the seal face materials must be
  able to withstand rubbing against each other at
  high load and speed.
• The best seal face materials have low friction,
  high hardness, good corrosion resistance and high
  heat conductivity.
• Examples of seal face materials Carbon graphite,
  Aluminium Oxide (Alumina), Tungsten carbide,
  Silicon carbide, Diamond coatings

13
Power Consumption of a liquid lubricated
mechanical seal
Important Points Face friction, churning and
soak in heat. Flush to dissipate the heat in
order to control the gap temperature. Coefficient
of friction can swing considerably during
operational transients. The key is to maintain
the gap profile as parallel as possible,
i.e.minimize distortions.
14
Classification of Mechanical Seal Mechanical
seals are classified by arrangement and
configuration. The wide variety of seal types is
due to the diversity of applications each
utilizing different machinery, fluids and
processes. Selection of the best type is not
always easy and straight forward as there is
usually a compromise between economical and
technical factors.
15
CLASSIFICATION BY ARRANGEMENT 1. SINGLE SEALS
(a) Single internally mounted seal, (b) Single
externally mounted seal Inside mounted pressure
on outside diameter of parts Outside mounted
pressure on inside diameter of parts The inside
mounted mechanical seal is most popular type of
single mechanical seal. Most seals are designed
to leak so that the liquid or gas will lubricate
the seal faces. Applications that do not utilize
substances that must be contained, such as
hazardous gases, dangerous chemicals or flammable
liquids, will generally use single seals. E.g
P-1560, P-1570
Inside Mounted-Pressure on outside diameter of
the parts
Outside Mounted-Pressure on inside diameter of
the parts
16
2. Dual seals Pressure between seals is higher
than seal chamber pressure (typically min. 30
psig). External fluid lubricates both sets of
faces. Leakage to the atmosphere is external
fluid. Is also called a "Double seal".
17
Pressure between seals is lower than seal chamber
pressure (typically atmospheric). External fluid
only lubricates the most outside set of faces.
The most inside faces are lubricated with the
pumped fluid. The most outside seal serves as a
safety seal or containment device. Leakage to
the atmosphere is external fluid, possibly mixed
with small amounts of pumped fluid. Is also
called a "Tandem seal". DOUBLE SEALS (a) Back
to back seals (b) Face to face seals Tandem
seals
18
Faces can be configured in several ways face to
back, face to face and back to back.
Mechanical seal classification by Consfiguration
i.e.design
19
1. Design Pusher vs. Non-pusher and Balanced vs.
Non-balanced Pusher vs. Non-pusher Pusher seals
utilize a dynamic secondary seal which moves
axially with the major seal face. Non-pusher
seals have a static secondary seal which stays
stationary against the shaft or sleeve.
Defined by the secondary seal type o-ring or
polymer wedge versus bellow, rubber or metal.

• Balanced Vs Non- balanced
• Balanced Seal
• Reduced closing forces
• Reduced power consumption
• For pressure up to 3000 psig
• Always recommended for volatile liquids

20

• Non- balanced
• High closing forces
• Low leakage
• For pressure up to 200 psig
• Not recommended for volatile liquids

2. Face Pattern
Examples are hydro-grooves, wavy faces, tapered
faces. Intended to increase opening forces in
order to improve lubrication. Friction is reduced
at the expense of a higher leak rate.
3. Stationary Spring Seals and Rotating Spring
seals
21

• Stationary spring seals are recommended by high
  speeds gt 5000 ft/min.
• Stationary spring seals are more suitable for
  machinery with inherently larger tolerances such
  a heavy duty slurry pumps and older pumps which
  have looser tolerances.
• 4. Cartridge seals and split seals
• Cartridge seals
• Seal are pre-assembled with sleeve and flange in
  one unit.
• Easy to install.
• No measurements during installation.
• Spring load is preset.
• May be factory tested with air, water or oil.
• More costly as compared to component seal.

22

• Split seals
• Seat is axially split.
• Does not require disassembly of the pump to
  install reduce down time.
• Leaks more than a conventional seal.
• More costly as compared to conventional seal.

Classification by containment devices
23

• Factors need to be considered in the application
  of a mechanical seal
• Here are some of the factors that need to be
  considered
• Pressure speed (PV limit Pressure x
  Velocity).
• Temperature.
• Fluid properties or characteristics.
• Run out of the shaft.
• Seal chamber type, available space radial and
  axial.
• Flushing/cooling arrangements, utilities in the
  plant.
• Mode of operation of the pump in the plant
  continuous, cyclic, multi-
• purpose.
• Static versus dynamic pressure.
• Test requirements.

24
Mechanical Seal Application Limit General
application guide per seal type Seal Type
Applications Non-pusher elastomeric bellows seal
A - B - D - E - L
Non-pusher metal bellows seal
A - D - E - F - I - J - L
Pusher O-ring secondary seal
A - B - G - H - K Pusher
polymer seal
A - B - G - K Pusher
stationary slurry seal
A - B - C - D - E - F - M Pusher
split seal
A - B - K Pusher dual gas
seal
A - B - E - F - G - H - L Fluid -
Characteristics A - Clean Lubricating B - Clean
Non-lubricating C - Viscous D - Clogging /
Scaling / Polymerizing / Fibrous E -
Crystallizing F - Molten Liquid G - Corrosive -
Acids
25
H - High Vapor Pressure I - Cryogenic J - High
Temperature (gt 260 ºC / 500 ºF) K - Solids (lt
0.1 by volume and less than 10 micrometers (394
micro inches) in size. L - Solids (lt 2 by volume
and less than 10 micrometers (394 micro inches)
in size M - Solids (gt 2 by volume).
26
Seal Faces Loading Devices Description of seal
faces loading devices Wide variety of types but
they can be categorized as either a spring or a
bellows of some kind. Working of a seal face
loading devices Seal face loading devices impart
an axial load to maintain contact when there is
no hydraulic pressure from the pumped medium. At
higher pressures the spring force is only a small
fraction of the overall face pressure. At face
speeds above 5000 ft/min the spring element is
installed stationary because of the centrifugal
effects.
27

• Flush arrangements
• It refers to the various methods used to
  lubricate, cool and remove deposits and heat in
  mechanical seal.
• Purpose of Flush
• Introduce fluid into seal chamber to improve the
  lubrication.
• Work to support the piping plan.
• Removal of seal generated heat.
• Removal of vapor bubbles.
• Protect against erosion
• Selecting a mechanical seal
• The mechanical seal should be selected according
  to the operating conditions at the seal location.
  These important factors must be considered when
  selecting a mechanical seal
• Shaft seal diameter
• Type of pumped medium
• Temperature
• Sealing pressure
• Shaft speed of rotation.

28
See next slides for Seal Piping plan P-1560,
P-1570, P-1580, P-1101 and P-4101
29
For P- 1560, P-1570 and P-1580 Propane Reflux
Pump (De-propanizer ), De-butanizer Reflux pump
and LPG Re-injection Pumps. The sealant is
supplied from a common sealant system (A-1502)
which supplies the P-1560, P-1570 and P-1580
pumps. Mechanical seal system of a single unit
has the following Accumulator Heat
Exchanger Pressure guage Temperature guage. See
Plan 53c
30
P-1560 A/B Duty Propane Reflux Pump
(Depropaniser) Manufacturer BW/IP
Inter.Co. Driver Electric Motor Motor Motor
Speed 2970 rpm Gear box None Pump
Type Horizontal Barrel Type Suctions Single Sta
ges Two Seals Pressurised Seal System Fluid
Pumped Propane Design Temperature -46C approx.
Sealant medium Aeroshell 31/41
31
P-1570 A/B Duty
Debutaniser Reflux Pumps Manufacturer
BW/IP International B.V. Driver
Electric Motor Motor Speed 2950 RPM Gear box
None Pump Type Horizontal Barrel
type Suctions Double Stages 5
stage Seals Pressurised System Fluid
Pumped Butane Temperature -8C approx. Sealant
medium Aeroshell 31/41
32
P-1580 A/B Duty
LPG Re-injection Pumps Manufacturer
Sundstrand Driver
Electric Motor Motor Speed 9466
RPM Gear Box Yes.
9419 rpm final gear Pump Type
Centrifugal Suctions
Single Stages
Single Seals
Pressurised System Fluid Pumped
LPG Temperature -30C approx. Sealant
medium Aeroshell 31/41
33
(No Transcript)
34
(No Transcript)
35
P-1101 A/B Amine Charge Pumps Manufacturer BW/IP
Driver Electrical motor Motor Power 850
kW Motor Speed 2980 rpm Gear Box
None Pump Type Centrifugal Suctions
Single Stages 4 Seals Crane
8B1/AR151 Fluid Pumped Lean Amine with
dissolved gases Temperature 55ºC It takes
fluid from the pump discharge through a pipe and
flushes the seal chamber and empty itself back
to the product
36
P-4101 Duty HTF Circulation Pumps Manufacturer BW
/IP Internationale BV Driver Electric
Motor Motor Speed 1450rpm Pump Type Centrifugal Su
ctions Double Stages Single Seals
Crane 215 metal bellows, mech seal cartridge
type. Fluid Pumped HTF Shell Thermia
B Temperature 139.6oC .
37
P-4111A/B Duty HTF Circulation
Pumps Manufacturer BW/IP Internationale
BV Driver Electric Motor Motor Power 580kW Motor
Speed 1450rpm Gear box None Pump
Type Centrifugal Suctions
Double Stages Single Seals Crane 215 metal
bellows, mech seal cartridge type. Fluid
Pumped HTF Shell Thermia B Temperature 191oC Flui
d is taken to the seal chamber from pump
discharge, cool the seal faces and discharges it
back through a discharge pipe to the product
line
38
(No Transcript)
39
(No Transcript)
40
Thank you