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  • Writer's picturekatiejobson


Updated: Mar 2, 2023

Mechanical seals are critical components in centrifugal pump systems. These devices preserve the integrity of the pump systems by preventing fluid leaks and keeping contaminants out. Mechanical seal systems are used on various seal designs to detect leakage, control the seal environment and lubricate secondary seals.

Depending on the pump type and the process variables, there are various mechanical seal types to choose from. Each seal variant has its unique design and characteristics which make it suitable for a specific application. Specialised Seals and Flow Solutions has decades of hands on experience selling, repairing and installing industrial mechanical seals and support systems, making us an authority in this area.

This article highlights the benefits and drawbacks of the different types of mechanical seals used in centrifugal pumps.

Different Types of Mechanical Seals for Centrifugal Pumps

Mechanical seal types vary in design, arrangement, and how they disperse the hydraulic forces acting at their faces. The most common seal types include the following:

  • Balanced seals

  • Unbalanced seals

  • Pusher seals

  • Non-pusher seals

  • Conventional seals

  • Cartridge seals

Balanced Seals and Unbalanced Seals

Balanced mechanical seal arrangements refer to a system where the forces acting at the seal faces are balanced.

  • As a result of the lower face loading, there is more even lubrication of the seal faces and longer seal life.

  • Balanced mechanical seals are particularly suited to higher operating pressures, typically above 200 PSIG.

  • They are also a good choice when handling liquids with low lubricity and higher volatility.

Unbalanced mechanical seal types are commonly employed as a more economical option to the more complex balanced seal.

  • Unbalanced seals may exhibit less product leakage due to tighter control of the face film.

  • Can exhibit much lower mean time between failure.

  • Unbalanced seals are not recommended for high pressure or most hydrocarbon applications.

Pusher and Non-Pusher Seals

Pusher seals utilise one or multiple springs to maintain seal closing forces. The springs can be in the rotating or stationary element of the mechanical seal.

  • Pusher type seals can provide sealing at very high pressures

  • The elastomer under the primary seal face can be subjected to wear as the face moves along the shaft/sleeve during operation.

Non-pusher seals utilise a metal or elastomeric bellows to maintain seal closing forces.

  • These seals are ideally suited to dirty and high temperature applications.

  • Bellows seals are limited to medium/lower pressure applications.

Both pusher and non-pusher designs are available in balanced and unbalanced configurations.

Conventional Mechanical Seals

  • Conventional seals are typically lower cost and often installed on general service equipment.

  • These seals require higher operator skill to service as they are installed as individual components.

Cartridge Type Seals

  • Cartridge type mechanical seals incorporate all of the seal elements into a single assembly. This dramatically reduces the potential for assembly error and the time require for seal replacements.

Key Considerations When Choosing Different Mechanical Seals for Pumps

When deciding on the type of seal system for a centrifugal pump, operators must choose according to their unique application. Failure to select the proper seal type can lead to loss of pump integrity, breakdowns and costly repairs. To avoid these undesirable results, all operators must consider the following factors before deciding.

Type of Fluid to Be Pumped

The fluid that you’re pumping is the single most important factor to consider when deciding on a seal type.

Factors such as cleanliness, lubricity and volatility will significantly affect the mechanical seal and seal support system design.

Pump Fluid Pressure

The amount of pressure exerted at a mechanical seal’s faces has a significant effect on its performance. If a pump is to be operated at low pressures, an unbalanced mechanical seal will be suitable. However, in conditions where higher pressures are anticipated, balanced seals will prove a more reliable solution.

Temperature Considerations

Balanced mechanical seals perform better than their unbalanced counterparts in conditions where the operating temperatures are higher than normal. Heat sensitive components are better preserved in balanced mechanical seals compared to other seal types.

Operator Safety Concerns

As it goes for all types of machinery, operator safety is the top priority. The use of double mechanical seals in centrifugal pumps provides additional protection as they have increased sealing capacity and are generally more reliable.

Let Specialised Flow Solutions Extend the Lifetime of your Mechanical Seals

Specialised Flow Solutions has a proven track record of providing the very best mechanical seal support to our clients.

Contact us online today for a quote or to learn more about the full range of products and services we offer.


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