What Is a Labyrinth Seal and How Does It Work

In the machinery industry, inadequate sealing can lead to leakage, contamination, and reduced performance, resulting in costly downtime and repairs.

Labyrinth seals offer a robust, non-contact sealing solution that addresses these challenges. By utilizing a complex path of interlocking components and leveraging centrifugal force and turbulence, labyrinth seals effectively minimize leakage and maintain optimal performance in various applications.

In this article, we will delve into the intricacies of labyrinth seals, exploring their components, design principles, and types. We will also discuss the materials used in their construction, their key advantages over other sealing methods, and their diverse applications across industries.

What is a Labyrinth Seal

A labyrinth seal is a type of non-contacting, mechanical seal designed to control leakage and reduce pressure differences between two areas in various rotary equipment applications. It consists of a series of interlocking teeth or grooves arranged in a complex, maze-like pattern between a rotating component (rotor) and a stationary component (stator).

The intricate design of the labyrinth creates an arduous path for fluids or gases to navigate, significantly restricting their flow from one side of the seal to the other. As the medium attempts to pass through the seal, it encounters multiple direction changes, contractions, and expansions. This tortuous route, combined with fluid dynamic effects, is what enables labyrinth seals to effectively minimize leakage.

Components of Labyrinth Seals

• Rotor: The rotor is the rotating part of the labyrinth seal assembly. It is typically attached to or integrated with the shaft that needs to be sealed. The rotor features a series of teeth or ridges that interlock with the stator component.
• Stator: The stator is the stationary part of the labyrinth seal, usually fixed to the housing or casing surrounding the rotating shaft. Like the rotor, the stator has a series of teeth or ridges that correspond to those on the rotor, creating a complex path for the fluid or gas being sealed.
• Interlocking Teeth: The interlocking teeth are the main sealing elements in a labyrinth seal. These teeth, present on both the rotor and stator, create a series of small clearances or gaps that make it difficult for the fluid or gas to pass through.
• Grooves: Grooves are the spaces between the interlocking teeth on the rotor and stator. These grooves create a tortuous path for the fluid or gas, forcing it to navigate through multiple turns and directional changes.
• Chambers: Labyrinth seals often feature chambers or cavities between the rotor and stator teeth. These chambers act as expansion spaces for the fluid or gas, allowing it to lose pressure and velocity as it moves through the seal.
• Ridges: In addition to the interlocking teeth, labyrinth seals may incorporate ridges or fins on the rotor or stator surfaces. These ridges further disrupt the flow of the fluid or gas, creating additional turbulence and resistance.

How Labyrinth Seals Work

Labyrinth seals prevent fluid leakage by creating a tortuous path that makes it difficult for the fluid to escape. As the fluid enters the labyrinth seal, it encounters a series of chambers formed by the interlocking teeth on the rotor and stator components.

Fluid Dynamics

The fluid is forced to navigate through these narrow chambers, losing kinetic energy with each turn. This energy loss occurs due to friction and turbulence generated within the chambers. As the fluid progresses deeper into the labyrinth, its pressure and velocity decrease substantially.

Turbulence

The sudden changes in the fluid’s direction and velocity as it navigates the labyrinth generate turbulent flow, which further impedes the fluid’s ability to leak through the seal. The turbulence also promotes the mixing of fluid particles, dissipating their energy and reducing the overall leakage rate.

Centrifugal forces

As the rotor spins, it imparts a centrifugal force on the fluid particles attempting to pass through the seal. This force directs the fluid particles away from the center of rotation and toward the outer edges of the seal chambers, making it more difficult for them to continue moving along the leakage path.

Pressure Breakdown

The pressure drop across each chamber in the labyrinth is determined by the fluid’s initial velocity and density, as well as the geometry of the labyrinth. With each subsequent chamber, the pressure continues to decrease until it equalizes with the external pressure at the labyrinth outlet.

By the time the fluid reaches the end of the labyrinth path, its pressure has dropped significantly, and its velocity is greatly reduced. This makes it much harder for the fluid to leak out, even with a non-contacting seal design.

Types of Labyrinth Seals

Labyrinth seals can be categorized into two main types based on their application: rotating shaft seals (dynamic) and non-rotating shaft seals (static).

Rotating Shaft Seals (Dynamic)

Rotating shaft seals, also known as dynamic labyrinth seals, are designed to prevent leakage along rotating shafts in various machinery. These seals are commonly found in turbines, compressors, and pumps. Dynamic labyrinth seals can be further classified into three subtypes:

1. Straight-Through Labyrinth Seals: In this design, the rotating and stationary components have teeth or fins that are arranged in a straight line, perpendicular to the shaft axis. The sealing effect is achieved through the creation of a series of small clearances between the rotating and stationary parts, which causes the fluid to lose pressure as it passes through each clearance.
2. Staggered Labyrinth Seals: Staggered labyrinth seals feature teeth or fins on the rotating and stationary components that are offset from each other. This arrangement creates a more tortuous path for the fluid, leading to improved sealing performance compared to straight-through designs. The staggered configuration helps to dissipate the kinetic energy of the fluid more effectively.
3. Stepped Labyrinth Seals: Stepped labyrinth seals can be further divided into two subtypes: convergent and divergent.
   • In a convergent stepped seal, the clearance between the rotating and stationary components decreases along the sealing path. This design accelerates the fluid flow, reducing its pressure and creating a more effective seal.
   • Divergent stepped seals have increasing clearances along the sealing path, which decelerate the fluid flow and cause a pressure recovery, improving sealing performance.

Non-Rotating Shaft Seals (Static)

Non-rotating shaft seals, or static labyrinth seals, are used in applications where there is no relative motion between the shaft and the housing. These seals are designed to prevent leakage between stationary components, such as in pipeline flanges, valve bonnets, and heat exchangers.

Static labyrinth seals rely on a series of interlocking teeth or grooves machined into the mating surfaces of the stationary components. The geometry of these seals creates a complex path that makes it difficult for the fluid to pass through, thus providing an effective sealing solution.

Common Materials

• Steels: Carbon steels, stainless steels, and alloy steels are widely used in labyrinth seal construction due to their strength, durability, and resistance to wear and corrosion. These materials are well-suited for high-temperature and high-pressure environments.
• Bronze: Bronze alloys, such as aluminum bronze and tin bronze, are popular choices for labyrinth seals because of their excellent wear resistance and low friction properties. Bronze seals are often used in applications involving rotating shafts.
• Polymers and Plastics: Engineering plastics, such as PTFE (polytetrafluoroethylene), PEEK (polyether ether ketone), and nylon, are increasingly used in labyrinth seal designs. These materials offer advantages like low weight, corrosion resistance, and self-lubricating properties, making them suitable for certain low-temperature and low-pressure applications.

Advantages of Labyrinth Seals

Effective Sealing Performance

Labyrinth seals provide reliable sealing performance by creating a tortuous path that makes it difficult for fluids to pass through. The interlocking teeth, grooves, and chambers create a series of pressure drops, effectively reducing leakage and maintaining the desired pressure differential.

Non-Contact Operation

The rotor and stator components do not physically touch each other, which minimizes friction and wear.

Tolerance to Shaft Misalignment

The clearances between the rotor and stator allow for small radial and axial movements, making labyrinth seals less sensitive to alignment issues compared to other seal types.

Reduced Maintenance

Labyrinth seals do not rely on wearing parts or consumable components, which minimizes the need for frequent replacements or adjustments.

Applications of Labyrinth Seals

Turbomachinery

Labyrinth seals are extensively used in turbomachinery, such as gas turbines, steam turbines, and compressors.

Aerospace Engines

In aircraft engines, labyrinth seals help to contain the high-pressure air and combustion gases within the engine, ensuring optimal thrust and fuel efficiency.

Pumps and Hydraulic Systems

Labyrinth seals are used in pumps and hydraulic systems to prevent fluid leakage and maintain system pressure. They are particularly effective in sealing high-viscosity fluids and slurries.

Industrial Gearboxes

In industrial gearboxes, labyrinth seals are employed to seal the interfaces between rotating shafts and housings. They prevent lubricant leakage and ingress of contaminants, which can cause premature wear and failure of gears and bearings.

Chemical and Petrochemical Processing

Labyrinth seals find applications in chemical and petrochemical processing equipment, such as reactors, distillation columns, and heat exchangers. They are used to seal rotating shafts and prevent leakage of process fluids, which can be corrosive, toxic, or flammable.