What is a Mechanical Seal?

A mechanical seal, also known as a face seal, is a device used to prevent fluid leakage. It consists of at least a pair of end faces perpendicular to the rotation axis. These faces remain in contact and slide relative to each other under the action of fluid pressure, the elastic force (or magnetic force) of the compensation mechanism, and the cooperation of auxiliary seals.

Mechanical seals are a type of shaft seal used in rotating machinery, such as centrifugal pumps, centrifuges, reaction kettles, and compressors. Due to their advantages of minimal leakage and long service life, mechanical seals are the most important shaft seal method in these devices worldwide.

Types of Mechanical Seals

Mechanical seals are categorized into several types based on different criteria:

  1. Based on Movement:
    • Rotary
    • Static
  2. Based on Springs:
    • Single Spring
    • Multiple Springs
    • Wave Spring
  3. Based on Balance:
    • Balanced
    • Unbalanced
  4. Based on Faces:
    • Single End Face
    • Double End Face
  5. Based on Compensation Elements:
    • Spring Mechanical Seals
    • Bellows Mechanical Seals

Spring Mechanical Seals:

  • Single Spring Type: Contains only one spring. Used for light loads and small shaft diameters.
  • Multi-Spring Type: Contains multiple springs. Used for larger shaft diameters. Offers uniform spring force distribution on the sealing end surface, though it is susceptible to corrosion.
  • Wave Spring Type: Features a shorter axial dimension compared to large springs, saving space.

Bellows Mechanical Seals:

  • Advantages:
    1. Simple structure, easy installation, strong adaptability, and a floating static ring.
    2. Better prevention of evacuation.
    3. Easy replacement and repair of the rotating ring.
    4. Compact structure, strong earthquake resistance, uniform bearing force, and good stability.
    5. Flange connection of the rotating ring and stationary ring, reducing dynamic leakage points.
  • Types:
    • Metal Bellows: Used in low and high-temperature environments.
    • Rubber Bellows: Used as an auxiliary seal for low-load mechanical seals, making them suitable for most light mechanical seals. Rubber bellows seals are convenient for efficient assembly line production, offering a good sealing effect at a lower cost, and gradually replacing soft packing seals in civil centrifugal pumps.

Importance of Mechanical Seals

Although sealing technology is not a leading technology, it is a decisive one. A mechanical seal, despite its small size, can determine the safety, reliability, and durability of machinery and equipment. In petrochemical plants, a leaking shaft seal in a pump kettle can lead to serious consequences, including work disruption, fires, explosions, equipment shutdowns, and personal injury.

In daily maintenance of equipment such as pumps and kettles, the maintenance workload of mechanical seals is significant. With advancements in mechanical seal technology, their role in pump maintenance will continue to grow.

Composition of a Mechanical Seal

A mechanical seal consists of the following components:

  1. Main sealing elements
  • Rotating ring: Rotates with the shaft and closely adheres to the stationary ring to form a sealing surface to prevent medium leakage. It is usually made of wear-resistant materials such as silicon carbide and cemented carbide.
  • Stationary ring: Fixed on the sealing cavity and is relatively stationary to the rotating ring. It also uses wear-resistant and corrosion-resistant materials and cooperates with the rotating ring to achieve the sealing function.
  1. Auxiliary sealing elements

Sealing ring: Including rotating ring sealing ring and stationary ring sealing ring. The rotating ring sealing ring mainly prevents leakage between the rotating ring and the shaft, and the stationary ring sealing ring prevents leakage between the stationary ring and the sealing cavity. Generally, it is made of elastic materials such as rubber and polytetrafluoroethylene.

  1. Elastic elements

Spring: Provides axial force to make the rotating ring and the stationary ring closely fit. The elastic force of the spring should be moderate. If it is too small, it will lead to poor sealing. If it is too large, it will increase friction and wear. In addition, there are other forms of elastic elements such as bellows.

  1. Transmission parts

Transmission pins, transmission seats, etc.: Used to transmit the rotation of the shaft to the rotating ring and make the rotating ring rotate with the shaft. The transmission parts should ensure synchronous rotation of the rotating ring and the shaft and at the same time not affect the sealing performance.

Standard Mechanical Seal Materials

Seal faces are characterized by their wear resistance and corrosion resistance. Common materials used for seal faces include:

The common materials that constitute the seal faces mainly include the following:

  1. Silicon carbide (SiC): It has extremely high hardness, wear resistance and corrosion resistance, and can maintain good sealing performance under harsh conditions such as high temperature, high pressure and high-speed rotation. It has good thermal conductivity, which helps to dissipate heat and reduce the thermal deformation of the seal face.
  2. Tungsten carbide (WC): It has high hardness, high strength and excellent wear resistance. It can withstand large loads and wear and is suitable for sealing occasions with high load and high wear.
  3. Graphite: It has good self-lubricating performance and can work effectively in the case of dry friction or less oil lubrication. It has good thermal conductivity and corrosion resistance and can adapt to certain temperature changes.
  4. Ceramics: Such as aluminaceramics, it has high chemical stability, high temperature resistance and good insulation performance. The smooth surface is conducive to reducing friction and wear.
  5. Cemented carbide: It has good comprehensive performance, including high strength, high hardness and good corrosion resistance, and can operate stably for a long time under harsh working conditions.

Each material has its unique advantages. When choosing, it is necessary to comprehensively consider factors such as pressure, temperature, medium and rotational speed according to the specific sealing working conditions to ensure the reliability and durability of the seal faces.

JUNTY can provide all kinds of standard and customized sealing rings. The auxiliary sealing materials include various types of rubber, such as NBR, EPDM, HNBR, FKM, CR, FFKM, and PTFE. The appropriate material should be selected according to the working conditions. Springs are always made of stainless steel, including AISI304, AISI316, Haste alloy, PH17-7, and AM350.

JUNTY group of companies is headquartered in Chicago, Illinois. We have been providing sealing products, wear-resistant parts, and components to the fluid and gas control industries all over the world for more than twenty years. We a professional and dedicated team with a deep understanding of our industry needs and the rotary equipment manufacturing business. We work closely with our clients on all aspects of their sourcing requirements thanks to our diverse engineering capabilities, from initial design through prototype testing to mass manufacturing. We are currently growing to meet the global demand from our clients for quality, engineering, and material selection. The long-term, mutually beneficial partnership with our business partners has always been our goal.