Brief overview about Mechanical seals

2. Seals are devices used to prevent or eliminate leakage of fluids
What is Seal?

3. Seal Classification
Seal
Static seals
Gasket Sealant
Dynamic seals
Rotating shaft
seal
Face seal
Axial seal
Mechanical
Seals
Radial seal
Lip ring seal Packing
Circumferential
split seal
Interstitial seal
Labyrinth seal Bush seal
Reciprocating
shaft seal
Packings Piston ring

4. 1. Set of primary seal faces: one rotary
and one stationary.
2. Set of secondary seals such as, O-
ring and shaft packing.
3. Mechanical seal hardware including;
gland ring, collar, compression ring,
spring and bellows.
The Basic Mechanical Seal

5. The primary seal is achieved by two
very flat, lapped faces which create a
difficult leakage path perpendicular to
the shaft. Rubbing contact between
these two flat mating surfaces
minimizes leakage. As in all seals, one
face is held stationary in housing and
the other face is fixed to, and rotates
with the shaft. One of the faces is
usually a non-galling material such as
carbon-graphite. The other is usually a
relatively hard material like silicon-
carbide. Dissimilar materials are usually
used for the stationary insert and the
rotating seal ring face in order to
prevent adhesion of the two faces.
Mechanical Seal Mechanism (How it’s work?)

6. 1. Between stationary element and
casing.
2. Between rotating element and
shaft.
3. Between mating surfaces of
stationary and rotating seal faces.
Main Sealing Points

7. Classified by arrangement
Mechanical seal
Single
Inside
Outside
Double
Dual pressurized
Dual Pressurized Gas
(Non-contacting)
Tandem
(unpressurized)
Cartridge
Classified by design
Mechanical Seal Classification
Mechanical seal
Balanced Unbalanced

8. Single Mechanical Seal
Sin gle I n s id e Sin gle Ou ts id e
Description
It is a mechanical seal with one set of primary seal (one dynamic
seal face). They called inside seals because the seal parts are
located inside the seal housing.
It is the most common type of mechanical seal for pumps.
It is a mechanical seal with one set of primary seal (one dynamic
seal face). They called outside seals because the entire rotation
portion of the seal is outside the seal chamber.
Advantage
• Can be easily modified to accommodate seal flush plan.
• Can be balanced to withstand high seal environment
pressures.
• Hardware items of the seal don’t come in contact with liquid.
Disadvantage
• Hardware items of the seal come in contact with liquid which
may corrosive.
• Pressure of sealed liquid pushes the two seal faces apart.
• Limited to sealing pressure 25 to 30 psig unbalanced and 60
psig balanced.
• Exposed to dust and other environmental contaminants.
Photo/Drawing

9. Double Mechanical Seal
D u a l P r e s s u r i ze d
D u a l P r e s s u r i ze d G a s
( N o n - c o n t a c t i n g )
Ta n d e m
( D u a l u n p re s s u r i ze d )
Description
Dual mechanical seal is a combination of two seals
mounted back-to-back with a non-hazardous barrier
liquid injected between the two seals at pressure
higher than pumped liquid pressure.
Dual pressurized gas mechanical seal is a combination
of two seals mounted back-to-back with a barrier gas
(normally N2) injected between the two seals at
pressure 25 to 30 psi higher than pumped liquid
pressure. When shaft begins to rotate, pressure is
built up within spiral grooves that machined in mating
rings which separates the seal faces. This effect result
in non-contacting faces at both dynamic seal faces.
Tandem mechanical seal is a combination of two seals
mounted back-to-front with a non-hazardous buffer
liquid injected between the two seals at pressure less
than pumped liquid pressure.
Applic
ation
Corrosive liquids, toxic liquids and liquids containing
abrasive solids.
Abrasive, flashing, flammable and toxic liquids.
Corrosive liquids, toxic liquids and liquids containing
abrasive solids.
Feature
Pumped liquid can’t leak into the environment.
Provide reduction in power consumed in seal (Less
mechanical losses).
If primary seal fails, end user can plan to
repair/replace seal in advance without any product
escaping to the environment if secondary seal still
alive.
Photo/Drawing

10. Cartridge Mechanical Seal
Cartrid ge Mech an ical Seal
Description
Mechanical seal Pre-mounted on a sleeve and fit directly to shaft
or shaft sleeve ( available single, double and tandem) .
Advantages
• No requirement for seal setting measurement for installation.
• Eliminate seal setting errors.
• Low maintenance cost.
Photo/Drawing

11. Balanced & Unbalanced Mechanical Seal
B alan ced Un b alan ced
BalanceRatio
The balance ratio of a mechanical seal is an area ratio and is related to the seal face load. Balance ratio
is defined as the ratio of the closing area to the opening area.
Balance Ratio < 1 Balance Ratio > 1
Advantages
• Less hydraulic force acting on seal faces.
• Generate less heat.
• Higher pressure limit.
• Can handle liquids with poor lubricity and high vapor
pressure.
• Inexpensive.
• Less leak.
• Stable when subjected to vibration, misalignment and
cavitation.
Disadvanta
ges
• Relatively higher cost.
• Very minor leak is expected.
• Higher Hydraulic force acting on seal faces.
• Low pressure limit.
Photo/Drawing

12. Piping Plan
API Mechanical Seal Piping Plan
Why flushing plan is required?
1. To lubricate and cool mechanical seal.
2. To remove foreign particles.
3. To remove carbon deposition and engrossed materials on mating surfaces.
4. Prevent seal from dry running.
5. To maintain the operational parameters of mechanical seal.
Mechanical Seal Type API Seal Plan
Single seal 01, 02, 11, 13, 14, 21, 23, 31, 32 and 41
Double seal 52, 53A, 53B, 53C and 54
Double seal (Gas Barrier) 72, 74, 75 and 76

13. Buffer and Barrier Fluid
Buffer Fluid Barrier Fluid
Characteristics of Buffer/Barrier
Fluid
• Safe to use, handle and store.
• Compatible with seal materials.
• Not a volatile organic compound, volatile hazardous
air pollutant or other regulated compound.
• Good flow qualities at operational temperatures
(including very low temperature service).
• Nonflammable.
• A stable liquid at ambient temperatures.
• Good lubricity.
• Non-foaming when pressurized.
• Good heat transfer properties.
• Low gas solubility.
• Compatible with process fluid.
• Inexpensive.

14. How to Install Mechanical Seal?

15. • Zero or minimal leakage.
• Elimination of shaft and sleeve wear.
• Low maintenance cost.
• Ability to seal higher pressure and more corrosive liquids.
• Lower mechanical losses compared to conventional packing.
Advantages of Mechanical Seal Over Conventional Packing

16. • Liquid type.
• Pressure.
• Temperature.
• Characteristics of liquid.
• Reliability and emission concern.
Mechanical Seal Selection Criteria

17. Mechanical properties
1. High modulus of elasticity.
2. High tensile strength.
3. Low coefficient of friction.
4. Excellent wear resistance.
Chemical properties
1. Corrosion resistance.
Mechanical Seal Material Properties
Thermal properties
1. Low coefficient of expansion.
2. High thermal conductivity.
3. Resistance to thermal shock.
4. Thermal stability.

18. Mating faces
1. Carbon-Graphite.
2. Tungsten Carbide(TC).
3. Silicon Carbide (SiC).
4. Ceramic.
Elastomers
1. Teflon.
2. Viton.
3. Buna N.
4. Silicone rubber.
5. Neoprene.
6. Butyl.
Mechanical Seal Material
Metals Parts
1. Stainless steel.
2. Bronze.
3. Hastelloy (super alloys).

19. Operational error
1. Dry running.
2. Suction chocking.
3. Foreign material.
4. Material incompatibility.
5. Abnormal process parameters.
6. Flushing plan off.
Maintenance error
1. Improper installation.
2. Shaft misalignment.
3. Shaft run out.
4. Failed bearing.
5. Unavailability of required flushing plan.
How Mechanical Seal Can Fail ?