Exploring Different Types of Mechanical Seals

I. Classification by application of the main machine

Mechanical seals can be classified by the application of the main machine into pump seals, kettle seals, turbine compressor seals, fan seals, refrigeration machine seals, and other main machine seals.

1. Pump mechanical seals

• Mechanical seals for various single-stage centrifugal pumps, multi-stage centrifugal pumps, vortex pumps, vacuum pumps, etc.
• Mechanical seals for internal combustion engine cooling water pumps, including mechanical seals for cooling water pumps of various automobiles, tractors, and internal combustion locomotives.
• Marine pump mechanical seals, including mechanical seals for various pumps on ships and vessels.
• Submersible electric pump mechanical seals, including mechanical seals for various submersible motors, submersible oil motors, and submersible brine motors.

2. Kettle mechanical seals

Including mechanical seals for various stainless steel kettles, enamel kettles, and glass-lined kettles.

3. Turbine compressor mechanical seals

Including mechanical seals for various centrifugal compressors and axial compressors.

4. Fan mechanical seals

Including mechanical seals for various ventilators and blowers.

5. Refrigeration machine mechanical seals

Including mechanical seals for various screw refrigeration machines and centrifugal refrigeration machines.

6. Other main machine mechanical seals

Including mechanical seals for separation machinery, washing machines, high-temperature dyeing machines, reducers, and reciprocating compressor crankcases.

II. Classification by principle of operation and structure

1. Classification by the number of sealing faces

(1) Single-face mechanical seals refer to mechanical seals composed of one pair of sealing faces.

(2) Double-face mechanical seals refer to mechanical seals composed of two pairs of sealing faces. Double-face mechanical seals are further divided into axially arranged and radially arranged double-face mechanical seals. Axial double-face mechanical seals are classified by the arrangement of the two sets of seals into:

• Back-to-back double-face mechanical seals refer to double-face mechanical seals where two compensating elements are installed between two pairs of sealing rings.
• Face-to-face double-face mechanical seals refer to double-face mechanical seals where two pairs of sealing rings are installed between two compensating elements.
• Face-to-back double-face (series) mechanical seals refer to double-face mechanical seals where one pair of sealing rings is installed between two compensating elements, and one compensating element is installed between two pairs of sealing rings.

(3) Multi-face mechanical seals refer to mechanical seals composed of more than two pairs of sealing faces.

2. Classification by the pressure condition of the sealing fluid

• Seals where the sealing fluid is in one pressure state are called single-stage seals.
• Seals where the sealing fluid is in two pressure states are called double-stage seals.
• Seals where the sealing fluid is in more than two pressure states are called multi-stage seals.

3. Classification based on the pressure exerted by the sealing fluid on the sealing end face

(1) Balanced mechanical seal refers to a mechanical seal where the pressure exerted by the sealing fluid on the sealing end face is unloaded (balance coefficient β<1). Balanced mechanical seals are divided into partially balanced mechanical seals and overbalanced mechanical seals based on the degree of unloading.

Partially balanced mechanical seal refers to a mechanical seal where the pressure exerted by the sealing fluid on the sealing end face is partially unloaded (balance coefficient 0<β<1). Overbalanced mechanical seal refers to a mechanical seal where the pressure exerted by the sealing fluid on the sealing end face is fully unloaded (balance coefficient β≤0).

(2) Unbalanced mechanical seal refers to a mechanical seal where the pressure exerted by the sealing fluid on the sealing end face is not unloaded (balance coefficient β≥1).

4. Classification based on whether the stationary ring is installed on the inner or outer side of the end cover (or equivalent part)

(1) Internally mounted mechanical seal refers to a mechanical seal where the stationary ring is installed on the inner side of the sealing end cover (i.e., the side facing the working chamber of the main machine).

(2) Externally mounted mechanical seal refers to a mechanical seal where the stationary ring is installed on the outer side of the sealing end cover (i.e., the side facing away from the working chamber of the main machine).

5. Classification based on whether the spring is placed inside the sealing fluid

(1) Internally spring-mounted mechanical seal refers to a mechanical seal where the spring is placed inside the sealing fluid.

(2) Externally spring-mounted mechanical seal refers to a mechanical seal where the spring is placed outside the sealing fluid.

6. Classification based on the number of springs in the compensation mechanism

(1) Single-spring mechanical seal refers to a mechanical seal where the compensation mechanism contains only one spring.

(2) Multi-spring mechanical seal refers to a mechanical seal where the compensation mechanism contains multiple springs.

7. Classification based on whether the compensation ring rotates with the shaft

(1) Rotating mechanical seal refers to a mechanical seal where the compensation ring rotates with the shaft.

(2) Stationary mechanical seal refers to a mechanical seal where the compensation ring does not rotate with the shaft.

8. Classification based on the direction of leakage of the sealing fluid between the sealing surfaces and the direction of centrifugal force

(1) Inward flow mechanical seal refers to a mechanical seal where the direction of leakage of the sealing fluid between the sealing end faces is opposite to the direction of centrifugal force.

(2) Outward flow mechanical seal refers to a mechanical seal where the direction of leakage of the sealing fluid between the sealing end faces is the same as the direction of centrifugal force.

9. Classification based on whether the back face of the compensation ring farthest from the sealing end face is on the high-pressure side or low-pressure side

(1) High-pressure back face mechanical seal refers to a mechanical seal where the back face of the compensation ring farthest from the sealing end face is on the high-pressure side.

(2) Low-pressure back face mechanical seal refers to a mechanical seal where the back face of the compensation ring farthest from the sealing end face is on the low-pressure side.

10. Classification based on the contact state of the sealing end faces

(1) Contact mechanical seal refers to a mechanical seal where the sealing end faces are tightly fitted by the elastic force of the elastic element and the pressure of the sealing fluid, usually under boundary lubrication conditions.

(2) Non-contact mechanical seal refers to a mechanical seal where a complete fluid film is formed between the sealing end faces by the action of fluid static pressure or dynamic pressure, forcing the sealing end faces to separate without rigid solid-phase contact. Non-contact mechanical seals are further divided into fluid static pressure mechanical seals and fluid dynamic pressure mechanical seals based on whether the sealing fluid film is a static pressure fluid film or a dynamic pressure fluid film.

Fluid static pressure mechanical seal refers to a mechanical seal where the sealing end faces are designed with a special geometry to create a fluid static pressure effect by introducing external fluid or the sealed medium itself through the pressure drop across the sealing interface.

Fluid dynamic pressure mechanical seal refers to a mechanical seal where the sealing end faces are designed with a special geometry to create a fluid dynamic pressure effect through relative rotation.

11. Classification based on the characteristics of the compensating elastic element

(1) Spring mechanical seal refers to a mechanical seal where the compensating element uses a spring, and the thrust generated by the compression of the spring causes the two end faces to press tightly together.

(2) Bellows mechanical seal refers to a mechanical seal where the compensating element uses a bellows or a combination of bellows and springs, and the thrust generated by the compression of the bellows or the combination of bellows and springs causes the end faces to press tightly together. Bellows mechanical seals are further divided based on their material.

• Metal bellows mechanical seal refers to a bellows mechanical seal made of metal. According to its manufacturing process and structural characteristics, metal bellows mechanical seals are further divided into welded metal bellows mechanical seals and hydraulic metal bellows mechanical seals.
• PTFE bellows mechanical seal refers to a bellows mechanical seal made of PTFE.
• Rubber bellows mechanical seal refers to a bellows mechanical seal made of rubber.

III. Classification by operating conditions and parameters

1. Classification by the applicability of different temperature ranges in the sealing chamber

• High-temperature mechanical seal refers to a mechanical seal that can be used when the temperature in the sealing chamber is greater than 150°C.
• Medium-temperature mechanical seal refers to a mechanical seal that can be used when the temperature in the sealing chamber is between 80°C and 150°C.
• Normal-temperature mechanical seal refers to a mechanical seal that can be used when the temperature in the sealing chamber is between -20°C and 80°C.
• Low-temperature mechanical seal refers to a mechanical seal that can be used when the temperature in the sealing chamber is below -20°C.

2. Classification by sealing pressure

• Ultra-high pressure mechanical seal refers to a mechanical seal that can be used when the pressure in the sealing chamber is greater than 15MPa.
• High-pressure mechanical seal refers to a mechanical seal that can be used when the pressure in the sealing chamber is between 3MPa and 15MPa.
• Medium-pressure mechanical seal refers to a mechanical seal that can be used when the pressure in the sealing chamber is between 1MPa and 3MPa.
• Low-pressure mechanical seal refers to a mechanical seal that can be used when the pressure in the sealing chamber is between atmospheric pressure and 1MPa.
• Vacuum mechanical seal refers to a mechanical seal that can be used when the pressure in the sealing chamber is negative.

3. Classification by the different levels of applicable sealing face linear speed

• Ultra-high speed mechanical seal refers to a mechanical seal that can be used when the average linear speed of the sealing face is greater than 100m/s.
• High-speed mechanical seal refers to a mechanical seal that can be used when the average linear speed of the sealing face is between 25m/s and 100m/s.
• General speed mechanical seal refers to a mechanical seal that can be used when the average linear speed of the sealing face is less than 25m/s.

4. Classification by the applicability of sealing media containing abrasive particles

Mechanical seal for abrasive media refers to a mechanical seal that can be used when the sealed media contains abrasive particles.

5. Classification by the corrosion resistance of the sealed media

(1) Mechanical seal for highly corrosive media, usually refers to a mechanical seal resistant to strong acids, strong alkalis, and other highly corrosive media.

(2) Mechanical seal for oil, water, and other weakly corrosive media, usually refers to a mechanical seal resistant to oil, water, organic solvents, and other weakly corrosive media.

6. Classification by shaft diameter

• Large shaft diameter mechanical seal refers to a mechanical seal with a shaft diameter greater than 120mm.
• General shaft diameter mechanical seal refers to a mechanical seal with a shaft diameter not less than 25mm and not greater than 120mm.
• Small shaft diameter mechanical seal refers to a mechanical seal with a shaft diameter less than 25mm.

IV. Classification by parameters and shaft diameter

1. Heavy-duty mechanical seal

Heavy-duty mechanical seals refer to mechanical seals that meet one of the following parameters and shaft diameters:

• Sealing chamber pressure greater than 3MPa.
• Sealing chamber temperature less than -20℃ or greater than 150℃.
• Average linear speed of the sealing end face not greater than 25m/s.
• Sealing shaft diameter greater than 120mm.

2. Light-duty mechanical seals

Light-duty mechanical seals refer to mechanical seals that meet the following parameters and shaft diameters:

• Sealing chamber pressure less than 0.5MPa.
• Sealing chamber temperature greater than 0℃ and less than 80℃.
• Average linear speed of the sealing end face less than 10m/s.
• Sealing shaft diameter not greater than 40mm.

3. Medium-duty mechanical seals

Medium-duty mechanical seals generally refer to mechanical seals that are between heavy-duty and light-duty mechanical seals.