Non-Contact Shaft Seals | Centritec Seals Manufacturer

An Overview of Seal Applications

Seals play a critical role in protecting rotating systems by keeping lubrication in and contaminants out of a controlled seal cavity. Non-contact seals are designed specifically for applications where fluids must remain contained between two elements, without physical contact that can cause wear or energy loss.

A typical sealing application includes a stationary component, a non-stationary (or rotating) element, and a controlled fluid cavity between them (See Fig. 1). Traditionally, basic lip seals have been applied in this type of environment. However, their limitations, especially in high-speed or high-temperature environments, prompted the development of more advanced industrial sealing solutions.

Non-contact shaft seals emerged as a high-performance alternative for applications involving extreme shaft speed or where the durability of a traditional lip seal was limited. Unlike lip seals, which maintain direct contact between a flexible sealing lip and the rotating surface, contactless shaft seal technology eliminates that friction. In lip seals, this constant contact creates wear on both surfaces and generates significant parasitic drag to the system. As speed increases, the lip can overheat, deform, or even lift away from the shaft due to centrifugal forces, ultimately causing seal failure. By contrast, centrifugal shaft seals and other non-contact options reduce wear, minimize drag, and improve reliability in rotating equipment seals.

Types of Centrifugal Shaft Seals in Contactless Shaft Seal Technology

Non-contact shaft seals are designed to seal without any physical contact between the rotating and stationary elements. In general, the benefits of non-contact seals include:

No parasitic drag
No wear on the rotating element
Long life
Reduced heat buildup in the sealing cavity
Extended bearing life.

The type of non-contact seal chosen for an application determines its specific benefits. The key to successfully employing any non-contact seal is to understand the sealing methods, and to select the appropriate seal configuration for each specific application.

Non-contact shaft seals available in today's marketplace can be classified by their design characteristics, and include:

the Labyrinth Seal
the Hybrid Labyrinth Seal
the Centrifugal Pressure Seal

Each type of seal has specific advantages and limitations. To determine the applicability of each seal, the engineer must examine the performance of the seal during each of three normal operating modes:

While the shaft is stationary and not rotating
While the shaft is accelerating/decelerating to its normal operating speed or speed range (or down to a stop or non-rotating mode of operation)
While the shaft is operating at its normal speed or within its operating speed range.

1. Standard Labyrinth Seals

Labyrinth seals offer a non-contact method to prevent leakage through a complex path, suitable for high-speed applications but may allow some weepage when stationary. There are several types of labyrinth seals. Typical labyrinth seals incorporate a "maze" or a set of rings in extremely close proximity, to capture the lubrication and push it back toward the controlled fluid cavity. Rings in close proximity form a barrier by shearing the fluid, centrifugally slinging the lubricants from the rotating seal element to the stationary seal element in a series of steps (See Figure 2).

The labyrinth seal is constrained in its ability to function with a wide variety of fluids due to its limited ability to centrifugally push the lubricants back into the controlled fluid cavity. In addition, it can only handle a limited volume of lubricating fluid in the controlled fluid cavity, and it requires high rotational speeds to seal adequately. The seal is not able to keep out external environmental contaminants entering the controlled fluid cavity when the seal is not rotating, and some fluid "weepage" is expected from the seal. In general, the standard labyrinth type seals have limited abilities when reviewed in terms of the three operational modes:

Operating Mode 1: Non-Rotating

The controlled fluid cavity is exposed to the environment
Lubricant can settle at the bottom and potentially weep out
Weepage increases with prolonged stationary periods

Operating Mode 2: Shaft Accelerating / Decelerating

Seal must maintain laminar flow of the lubricant to prevent splashing and leakage
High-viscosity lubricants help reduce splashing
Any contaminants present on the stationary shaft can be pulled into the fluid cavity
Fluid level must be carefully maintained to avoid overflow

Operating Mode 3: Normal Operating Speed

Seal deflects fluid back into the cavity, maintaining effective sealing
High rotation speeds are required for reliable performance
Open to environmental contamination during operation
Requires precise axial alignment between rotating and stationary components
Susceptible to leakage if vibration or axial movement occurs

2. Hybrid Labyrinth Seals

Hybrid labyrinth seals incorporate contact elements that disengage at operational speeds, balancing sealing effectiveness with reduced wear. The hybrid labyrinth seal has been modified by adding a contact seal component designed to centrifugally lift off the rotating shaft when the seal is operating at normal speeds. This modification solves some of the limitations of the standard labyrinth seal, and makes it function more like a contact lip seal. In addition, a lip seal component can be incorporated such that it will only make contact at lower speeds and will centrifugally lift from the contact surface at higher speeds. While the hybrid labyrinth seal does solve the problem of contaminants entering the controlled fluid cavity when the seal is not rotating, it adds challenges in mounting the seal and controlling axial movement, and reduces the efficiency of the seal by adding a contact element.

In general, the hybrid labyrinth type seals have limited capabilities when reviewed in the three operating modes, but in the proper applications they can perform adequately. Hybrid labyrinth type seals offer additional features over the standard labyrinth seal but still have some limitations:

Operating Mode 1: Non-Rotating

The controlled fluid cavity is not fully open to the environment
Some fluid weepage is still possible due to the design of the lifting mechanism
Fluid may settle and collect at the bottom of the seal
Weepage risk increases with longer stationary periods

Operating Mode 2: Shaft Accelerating / Decelerating

Shaft and seal accelerate together; fluid must remain in laminar flow to avoid splashing
High-viscosity lubricants can help limit splashing and leakage
Parasitic drag is present until the contact element lifts off the rotating shaft
At high enough speeds, the seal performs similarly to a non-contact labyrinth seal
Proper operating speed is essential for reliable lift-off and sealing performance

Operating Mode 3: Normal Operating Speed

At full speed, the seal centrifugally lifts the contact element, reducing drag and wear
Fluid is pushed back into the seal cavity, maintaining a controlled seal environment
Like the standard labyrinth seal, the hybrid seal remains open to external contaminants
Contaminants can be pulled into the cavity during operation
Precise axial alignment is required between rotating and stationary components
Axial movement or vibration can compromise the seal’s effectiveness and cause leakage

Our experts have detailed tips about centrifugal pressure seals vs labyrinth seals, including specifications regarding speed, operating pressures, temperature range, and more.

3. Centrifugal Pressure Seals

Centrifugal pressure seals are non-contact shaft seals that utilize a rotating chamber within the seal to develop internal pressures and pump the sealing fluid back into the controlled fluid cavity, offering superior sealing in both horizontal and vertical shafts with minimal maintenance. (See Figure 3).

The double seal illustrated in Figure 3 will pump the contaminants out of the seal from the nonfluid side of the seal as well as pump the lubricating fluid back into the controlled fluid cavity.

The rotating chamber method significantly reduces the operational speed requirements of the typical non-contact seal and allows the use of extremely low-viscosity fluids, even water. The more fluid that passes from the controlled fluid cavity into the rotating chamber, the greater the pressure inside that chamber to return the fluid to the controlled fluid cavity. The fluid in the controlled fluid cavity will continue to fill the rotating chamber in the seal, until the pressure from the fluid in the rotating chamber is in balance with the pressure in the controlled fluid cavity. At this point the seal will continue to move fluid in and out of the rotating chamber to maintain a pressure balance with the controlled fluid chamber.

The centrifugal pressure seal is still a non-contact seal that solves the alignment issues of other labyrinth seals and actually pumps fluids to create a pressure differential between the environment and the controlled fluid cavity. This pressure differential also prevents contaminants from entering the seal's fluid chamber. These advantages are not available in either the standard contact lip type seal or the labyrinth seals. The advantages are clearer when looking at the three operational modes:

Operating Mode 1: Non-Rotating

In a double seal setup, the controlled fluid cavity is partially open to the non-fluid side
Contaminants may enter the non-fluid chamber when stationary, but are expelled upon acceleration
Wrapped chamber design prevents fluid leakage when not in motion
Ideal for applications requiring leak-free idle states

Operating Mode 2: Shaft Accelerating / Decelerating

Splashing is eliminated by internal pumping discs that maintain laminar flow
Seal is effective even with low-viscosity fluids like water
The external rotational chamber design captures fluid away from the shaft
Operates at much lower speeds than standard or hybrid labyrinth seals
Acceleration/deceleration leakage risks common in other seal types are not a concern

Operating Mode 3: Normal Operating Speed

Actively pumps fluid back into the controlled cavity, maintaining consistent pressure
No minimum high-speed threshold required for effective operation
Pumps contaminants out of the non-fluid chamber, whether liquid or gas
Creates a pressurized seal cavity, allowing it to stay full without leaking during operation
Tolerates vibration and misalignment, reducing maintenance demands
No need for precise axial alignment between rotating and stationary components

Learn more about centrifugal pressure non-contact seal design from our experts and reach out with questions. Our team is available to answer your questions or provide a quote.

Non-Contact Shaft Seals: Summary

There are currently three types of non-contact shaft seals available in the marketplace: the Labyrinth Seal, the Hybrid Labyrinth Seal and the Centrifugal Pressure Seal. Each offers a different technological solution to a shared engineering challenge. Selecting the right sealing solution requires a clear understanding of each application's demands and the specific performance characteristics of each seal type.

Centritec Seals’ centrifugal shaft seal design offers distinct advantages over traditional options. Unlike standard contact lip seals, Centritec’s non-contact design tolerates greater shaft misalignment, simplifies installation and maintenance, and significantly reduces long-term operating costs. These benefits make it an ideal choice for demanding rotating equipment seal applications where downtime and energy loss must be minimized. The following table highlights some of the operating characteristics among the three seal designs:

	Labyrinth Seals	Hybrid Labyrinth Seals	Centrifugal Pressure Seals
Non-Rotating	Weepage Open to external environment	Little weepage Closed to external environment	No weepage Partially open to external environment but will pump out during operation
Shaft Accelerating / Decelerating	Fluid levels needs to be limited in cavity Non-laminar fluid flow not tolerated Splashing not tolerated Fluid viscosity limited Shaft alignment critical	Fluid levels need to be limited in cavity Non-laminar fluid flow not tolerated Splashing not tolerated Fluid viscosity limited Shaft alignment critical	No splashing issues Full fluid cavity tolerated Viscosity of fluid is not an issue
Normal Speed	Alignment is critical, axial and radial movement will cause leaks and failure	Alignment is critical, axial and radial movement will cause leaks and failure	Vibration and misalignment tolerated

When the proper seal is selected, especially one engineered for performance and reliability, the rewards are significant:

Lower maintenance costs
No unplanned down-time due to seal wear/parts failure
Higher efficiency by eliminating parasitic drag torque
Increased bearing life through reduced heat generation

Contact Our Experts About Non-Contact Shaft Seals

Our non-contact shaft seals are crafted to deliver superior quality and reliability. With a wide range of sizes and configurations, we offer flexible solutions tailored to your specific needs. Our skilled engineers are ready to collaborate with you to develop customized seal designs that optimize your application’s performance.

If you have questions about our non-contact shaft seal manufacturing solutions, please reach out to our team or fill out the form on this page and we will be in contact shortly.

Published: November 29th 2011 • by Michael E. Gamache, President

©The Carlyle Johnson Machine Company, LLC and Centritec Seals, LLC., all rights reserved. Information contained herein is intended for illustrative purposes only. Individual projects and applications vary significantly and valves should be specified for specific applications.

Contact Centritec Seals for more information on our centrifugal seal manufacturer services, or to request a quote for your application.