Basic fundamentals and types of mechanical seals used in different types of rotary equipment. ie: centrifugal pumps

1. FUNDAMENTALS OF MECHANICAL
SEALS
Presented By: Avdhesh Kumar
Engineer
SAP-Mechanical

2. Tables of content.
Historical development of a Mechanical seal
Reason for using Mechanical seal
Types of seals
Static Seals(Gasket, O rings)
Dynamic Seals(Gland rope, Mechanical seal)
Working of mechanical seal
Single seal and Dual seal
Balanced seal and Non balanced seal
Single spring and multi spring seal
Pusher and Non pusher Seal
Material of construction of mechanical seal

3. Historical Development of a Mechanical
seal
• By the 1930’s, 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 1940’s, 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. Cross section view of pump with mechanical seal

5. Pumping liquid

6. Reasons for using Mechanical seal:
To minimize leakage
To prevent toxic fluids escaping to atmosphere
To reduce power loss.
Advantages of Using cartridge seal
Increased Reliability
Fits multiple types of pumps
Reduced downtime
Increased operating profits.

7. Types of seals
• Static seals
• Dynamic seals

8. STATIC SEALS
Sealing takes place between two parts that don’t move in
relation with each other.
Application
- Pipe flanges ,vessel /Tower nozzles, pump casing
joint
- Fan /Blower casing joint , Compressor casingjoint.
- Turbine casing joint, Heat exchangerjoints
Types
- Gaskets
- O-rings
- Liquid gaskets

9. 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
Ageing
Corrosion resistance

10. Classification of Gaskets
•Non-metallic gaskets
•Metallic gaskets
Non-metallic gaskets
Asbestos
Cork and rubber
PTFE

11. METALLIC GASKET
Corrugated
Plain
Asbestos filler
Metal clad
Soft material like asbestos CAF enclosed in metal
covering .
Provides additional mechanical strength
Spiral wound
Alternate layers of v- sections , metallic strip and
non- metallic filler compressed to a predetermined
amount
Metal – SS , Monel , Inconel , Titanium.
Fillers – Asbestos fibres , PTFE lead, ceramic paper,

12. 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

13. GLAND PACKING
 Enclosed in a stuffing box
 Compressive force by tightening the glandplate
produces radial pressure
 Slight leakage is allowed for lubrication
 Periodic retightening of gland necessary forwear
compensation.
 Lantern ring for cooling /lubrication
Stuffing box pressure No of rings
(bar)
up to 35 4
35-70 6
70-140 8
140 10

14. Gland packing
Braided by PTFEfibre
yarns and used inacids,
alkalis, gas, ammonia,
chemicals, etc.
The packing with PTFE
impregnated (YP006)are
also available.
Spec:6mm - 50mm

15. GLAND PACKING WITH PERMISSIBLE LEAKAGE

16. MECHANICAL SEALS
Components
1. rotary seal face
2. stationary seal face
3. springs
4. retainer
5. sealing /flushing media
6. o-rings

17. Shaft
Stuffing box
Retainer Spring Static sealDynamic seal
Liquid
Bolt for locking
Seal
follower
Gasket
Secondary
seal

18. PRICIPLE OF MECHANICAL SEALS
In Mechanical Seals, the Sealing Surfaces Of Every
Kind Are Located In APlane Perpendicular To The
Shaft And Usually Consist Of Two Highly Polished
Surfaces Running Adjacently.
One Surface Being Connected To The Shaft And The
Other to The Stationary Portion Of The Pump. The
Polished Surfaces Which are of dissimilar materials
Are Held In Continual Contact By a Spring, forming a
Fluid Tight Seal Between The Rotating And
Stationary Members With Very Small Frictional
Losses .

19. WORKING

20. Discharge
Seal flushing line , liquid took from
discharge line
Static &dynamic seal

21. MECHANICAL SEALS
CLASSIFICATION
By arrangement
1.Single seal
- Inside mounted / Outside mounted
2. Multiple design
- Double seal/ Tandem seal
By design
1.Unbalanced seal
2. Balanced seal
3. single spring
4. Multiple spring
5. Pusher seal
6. Non – pusher seal

22. SINGLE SEALS
 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.

23. Shaft
Seal
follower
Stuffing box
Retainer Spring
Static sealDynamic seal
Liquid
Gasket
Secondary seal
Inside mounted mechanical seal

24. Shaft
Seal
follower
Stuffing box
Retainer
Spring
Static seal
Dynamic seal
Liquid
Gasket
Secondary
seal
Outside mounted mechanical seal
Liquid

25. 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”
• Leakage to the atmosphere is external fluid, possibly mixed
with small amounts of pumped fluid.
Is also called a "Tandem seal".

26. Static seal
Dynamic seal
Liquid
Gasket
Secondary
seal
Barrierfluid1barmore
than process
Process liquid

27. Balanced Seal
Reduced closing forces
Reduced power consumption
For pressure up to 3000 psig
Always recommended for volatile liquids
The opening force is always the area of the sealing faces.
The balance ratio is then Ac/Ao. A seal with a balance ratio
less than 100 percent is called a balanced seal.
Ac= Closing Area
Ao= Opening Area

29. Non- balanced Seal
• A seal with a balance ratio greater than 100
percent is called an unbalanced seal. Most
balanced seals have a balance ratio between 60
and 90 percent. Most unbalanced seals have a
balance ratio between 110 and 160 percent.
High closing forces
Low leakage
For pressure up to 200 psig
Not recommended for volatile
liquids

30. SINGLE SPRING SEALS

31. SINGLE SPRING SEALS
Advantages:
• low starting torque
• non-clogging
• low spring constant
Limitation:
• due to single spring the face loading is not along the periphery
of the seal Faces.(not recommended for high rotational speed)
• Require long axial space.

32. MULTI SPRING SEAL

33. MULTI SPRING SEAL
• Number of small springs are used on the periphery of the
seal face to give a uniform face loading.
• These seals are compact in nature and are universally used on
most of the clear fluids.
• Due to uniformly loaded seal faces the multi spring seals are
a must for high rpm application.

34. MULTI SPRING SEAL
Advantages:
• compact in comparison with single spring seal.
•spring load uniform i.e. Uniform face loading.
• can be given for higher speed than single spring.
• for each seal size different spring not required.
Limitation:
• more expensive.
• spring clogging possible for dirty liquids.

35. Pusher vs. Non-pusher seal
• 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

36. PUSHER SEAL TYPE
Non- pusher seal type(metal bellow)

37. 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
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.

38. MOC – MECHANICAL SEALS
Primary seal
1.Ceramic
2. Carbon
- Resin impregnated – corrosive applications
- Antimony impregnated – non-corrosive
3. Tungsten carbide
- Ni binder
- Co binder
4. Silicon carbide
Secondary seal
Elastomers - Nitrile , Neoprene ,Butyl, Hypalon
Non –Elastomers - PTFE, Graf oil
Spring
SS 304, SS 316, Hastalloy, Monel, Alloy-20