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What are Mechanical Seals

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1. 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. – PowerPoint PPT presentation

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Title: What are Mechanical Seals


1
What Are Mechanical Seals?
  • Sap Parts
  • Manufacturer-Designer-OEM Supplier

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2
Meaning 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'.

3
Types 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

4
Types 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

5
Why 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.

6
Why 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.

7
Why 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
8
Why Use Mechanical Seals?
9
Mechanical 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.

10
A 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.

11
A few facts about the leakage (and wear)
behaviour of contacting mechanical seals
12
A 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.

13
MECHANICAL 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
  1. Requires more space than radial lip seals.
  2.  Cannot handle axial end play.
  3. Sealing faces must be finished smooth (0.08 to
    0.4 micrometer) and can get easily damaged.
  4. High initial cost.

16
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