Title: What are Mechanical Seals
1What Are Mechanical Seals?
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2Meaning of Mechanical Seals
- A mechanical seal is a device that helps join
systems or mechanisms together by preventing
leakage (e.g. in a plumbing system), containing
pressure, or excluding contamination. - The effectiveness of a seal is dependent on
adhesion in the case of sealants and compression
in the case of gaskets. - A stationary seal may also be referred to as
'packing'.
3Types of Seals
- Induction sealing or cap sealing
- Adhesive, sealant
- Bodok seal, a specialized gas sealing washer for
medical applications - Bridgman seal, a piston sealing mechanism that
creates a high pressure reservoir from a lower
pressure source - Bung
- Compression seal fitting
4Types of Seals
- Diaphragm seal
- Ferrofluidic seal
- Gasket or Mechanical packing
- Flange gasket
- O-ring
- O-ring boss seal
- Piston ring
- Glass-to-metal seal
- Glass-ceramic-to-metal seals
5Why Use Mechanical Seals?
- 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.
6Why Use Mechanical Seals?
- 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 seal has been said that it requires
high initial cost and is hard to handle, but it
is now highly valued as an important functional
part of the equipment, which enables long
continuous operation of the production process of
equipments and thus finally gives considerable
profit to the operation.
7Why Use Mechanical Seals?
Comparison Between Mechanical Seal and Gland Packing Comparison Between Mechanical Seal and Gland Packing Comparison Between Mechanical Seal and Gland Packing
Mechanical Seal Gland Packing
Leakage Extremely small or none Certain leakage is necessary to avoid seisure
Life Long with appropriate design and material Comparatively short as it wears and periodical tightening is required
Wear of shaft and sleeve Spring load keeps faces in contact if faces wear Periodical tightening required and must be replaced if wear of shaft or sleeve becomes excessive
Power Loss Small as frictions area are coefficient and small (Energy Saving Type) Big as friction area and coefficient area are large
Operating Range (Pressure Temp.) Applicable widely with appropriate materials and design Limited application due to keeping leakage small
Cost Running cost is low as maintenance is not necessary Running cost is high due to necessary maintenance
8Why Use Mechanical Seals?
9Mechanical Seals Operating Principles
- Essential elements of a mechanical seal
- These are the three essential elements of a
mechanical seal - Seal faces one rotating with the shaft and one
stationary in the pump casing, cover or flange. - Secondary seals one to seal the rotating face to
the shaft and one to seal the stationary face to
the pump cover or flange. - Metal parts to transmit torque and to provide an
axial mechanical force to load the faces. - Essential requirements for proper operation of a
mechanical seal - 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.
10A few facts about the leakage (and wear)
behaviour 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.
11A few facts about the leakage (and wear)
behaviour of contacting mechanical seals
12A few facts about the leakage (and wear)
behaviour of contacting mechanical seals
- 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. - The large majority of mechanical seals never wear
out and are removed from service for some other
reason. - Seal failures occur for a wide range of reasons.
- Some failures occur as an interaction with the
tribology of the interface.
13MECHANICAL SEAL COMPONENTS
- The Basic components in a mechanical seals
include the following - A stationary sealing face.
- A Rotating sealing face
- A Static secondary seal for stationary face.
- A Static secondary seal for rotating face.
- A spring or a bellow to press the sealing faces
together. - A system to flush seal area.
- A method to prevent slippage of sealing faces
(Keyways, pins or secondary seal friction).
14 ADVANTAGES OF MECHANICAL SEALS
- Handles all types of fluids (Acids, salts and
abrasive particles) - Handle slightly misaligned / non concentric
- Handle Bi-directional shaft rotation, large
pressure, temperature and speed excursions. - Shaft condition is not critical (Finish
roughness, roundness, hardness and material) - Operation does not cause shaft wear.
- Long operating life.
- Positive sealing for food processing, hazardous
chemicals and radioactive fluids.
15 DISADVANTAGES OF MECHANICAL SEALS
- Requires more space than radial lip seals.
- Cannot handle axial end play.
- Sealing faces must be finished smooth (0.08 to
0.4 micrometer) and can get easily damaged. - High initial cost.
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