Mechanical seals are essential for managing fluids effectively and are available in a variety of designs like single, double, and specialty seals. Each type is tailored to meet specific industrial needs, including pressure handling, temperature resilience, and installation complexity.a
This article explores the different mechanical seal types and their applications, helping you choose the right one for your needs.
Key Takeaways
- Single Mechanical Seals: These are available in various types such as unbalanced, balanced, pusher, non-pusher, conventional, and cartridge.
- Double Mechanical Seals: These include configurations like tandem and back-to-back. They utilize barrier or buffer fluids to enhance leak prevention and maintain fluid separation.
- Specialty Seal Arrangements: This category encompasses split seals, gas lubricated seals, and bellows seals. These designs address particular challenges such as ease of maintenance, capability to run dry, and operation under extreme conditions.
- Gas Lubricated Seals: These seals are engineered to minimize friction and heat, making them ideal for scenarios where dry running is necessary. They often employ advanced technologies such as spiral grooves to effectively form a gas film, reducing wear and extending seal life.
- Bellows Seals: Specifically designed to withstand high temperatures and pressures.
Single Seals
Unbalanced Vs Balanced Seals
Unbalanced seals are simpler: the entire face of the seal feels the full pressure of the system it’s part of. This direct exposure means these seals press very tightly together. The downside? Under too much pressure, they can warp or overheat, making them less effective in high-pressure scenarios. Typically, they’re used in lower-pressure environments.
Balanced seals have a special geometry that limits the amount of the seal’s face exposed to intense pressure. This design reduces the force pushing the seal faces together, which helps distribute pressure more evenly. As a result, balanced seals operate better under higher pressures, maintaining their shape and efficiency without overheating. The trade-off is that they generally cost more due to their complex design.
Pusher Vs Non-Pusher Seals
Pusher seals use a dynamic O-ring that moves axially along the shaft. This design helps adjust for wear and misalignment. However, they may not perform well with abrasive fluids as the moving O-ring can get stuck, known as seal hang-up.
Non-pusher seals use a flexible bellows instead of a moving O-ring. This bellows adapts to changes, maintaining the seal integrity without axial movement. They excel in handling high temperatures and are less prone to hang-ups.
Yet, they might require special materials to withstand corrosive environments and typically handle lower pressures. Although effective, non-pusher seals can be more expensive.
Conventional Vs Cartridge Seals
Conventional seals are often less expensive initially but require expert installation. This precision ensures they align properly on the pump shaft, which is crucial to prevent early failures.
Cartridge seals cost more upfront but are easier to install. They come fully assembled, which reduces the likelihood of errors during installation. This design also offers added protection for the pump shaft and shaft sleeve, which can lead to lower maintenance costs over time.
However, cartridge seals are not as versatile as conventional seals when it comes to certain types of pump applications, such as those involving impeller installation in submersible pumps. Conventional seals are preferable in these scenarios due to their adaptability.
Double Seals
Tandem Vs Back-To-Back Orientation
In the tandem setup, a secondary seal acts as a safeguard, providing a backup in case the primary seal fails. This secondary seal is lubricated by a buffer fluid, which is kept at a lower pressure than the fluid being sealed. This is particularly useful for enhancing the reliability of the seal system without exposing the secondary seal to high pressures.
The back-to-back configuration places the seals opposite each other. Here, a barrier fluid, maintained at a higher pressure than the process fluid, lubricates the seals. This setup is crucial when handling hazardous fluids. By maintaining the barrier fluid’s pressure above that of the process fluid, it ensures that any leakage is pushed back, preventing dangerous chemicals from escaping into the environment.
Pressurized Vs Unpressurized Barrier Fluid
When a pressurized barrier fluid is used, it is kept at a higher pressure than the process fluid. This setup helps to prevent leaks by pushing any escaping fluid back into the process stream. For this method to work effectively, it’s essential that the barrier fluid—whether it’s water, glycol solutions, or oils—is compatible with the process fluid. This compatibility prevents chemical reactions or other issues that could arise if the fluids were to mix.
Unpressurized buffer fluid is maintained at a lower pressure compared to the process fluid. Here, the design intentionally allows some process fluid to leak into the buffer chamber. Because the buffer fluid does not mix with the process fluid, its compatibility is less critical, which allows more flexibility in choosing suitable fluids for the buffer chamber.
Specialty Arrangements
Split Seals
Split seals significantly simplify the maintenance of large machinery by enabling installation directly around the shaft. This feature eliminates the need to dismantle other machinery components, effectively reducing downtime. These seals are especially advantageous in environments where removing heavy parts is not feasible.
Unlike traditional cartridge seals that come as a single unit, split seals are designed in multiple sections. This segmented design speeds up the installation process, making it easier to handle maintenance for cumbersome equipment. However, the segmented nature of split seals also introduces more potential paths for leaks compared to their one-piece counterparts.
Despite the increased risk of leakage, technological improvements in mechanical seal designs have enhanced the sealing capabilities of split seals. Nowadays, their performance can compete closely with that of traditional intact cartridge seals.
Gas Lubricated Seals For Dry Running
Gas lubricated seals designed for dry running incorporate sophisticated mechanisms such as spiral grooves and Rayleigh pads. These structures facilitate the formation of a thin layer of gas between the seal faces, ensuring they do not touch each other.
Typically, materials like carbon and silicon carbide are used due to their durability and performance in dry environments. These materials are robust enough to withstand the lack of lubrication and the heat generated during operation.
Support systems for these seals are also vital. They need to maintain precise gas pressure and ensure the gas is clean to avoid operational failures.
Bellows Seals For High Temperature/Pressure
Bellows seals are constructed entirely from metal, which allows them to operate efficiently in temperatures exceeding 400°F (200°C), and can even handle up to 800°F (425°C) or more. This capability is crucial for industries dealing with hot fluids such as hydrocarbons and aggressive chemicals.
The structural integrity of bellows seals is reinforced by their double-ply or laminated designs. This construction is specifically tailored to withstand pressures that surpass 1000 psi (70 bar). Such robust build quality ensures that the seals can maintain their functionality under severe stress without failure.
Materials used in bellows seals, such as Inconel or Hastelloy, are selected for their exceptional resistance to corrosion. In environments where harsh chemicals are present, ensuring that the seals do not degrade or fail prematurely.
Furthermore, many bellows seals are designed with balanced face loading. This feature plays a critical role in distributing the pressure uniformly across the seal faces. Even distribution of pressure helps in minimizing heat generation and deformations during operation, thereby enhancing the overall performance and extending the lifespan of the seals.
How To Select The Right Mechanical Seal
When selecting the right mechanical seal, you must first consider the specific operating conditions it’ll face. These conditions influence the choice of materials and the type of seal design that will provide peak performance. Analyze variables such as temperature, pressure, and fluid properties to make sure you select a seal that meets your system’s requirements efficiently and effectively.
Operating Conditions
- Type of Equipment: Consider the type of equipment the mechanical seal will be used with, such as pumps, mixers, or agitators, as different equipment types have varying requirements for mechanical seals.
- Shaft Size and Operational Speed: Analyze the shaft size and operational speed of your equipment, as these are crucial factors in selecting the right seal materials and design to prevent seal failure.
- Operating Temperature and Pressure: Take into account the operating temperature and pressure within the equipment, as high temperatures and pressures can compromise the seal’s integrity, necessitating seals capable of withstanding extremes.
- Fluid Viscosity and Presence of Solids: Consider the fluid’s viscosity and whether solids are present, as these factors influence the seal design needed to prevent leaks, with thicker fluids or those containing solid particles requiring a robust seal design.
- Compliance with Environmental Regulations: Ensure compliance with environmental regulations by selecting seals that meet necessary emission standards, to avoid regulatory issues while suiting machinery and handling requirements.
Seal Design Considerations
- Balanced and Unbalanced Designs:
- Balanced seals are preferable for high-pressure applications, offering greater performance and durability.
- Unbalanced seals are more economical and suitable for less demanding applications.
- Arrangement: Single seals suffice for simple systems, while double seals are recommended for hazardous or costly fluids to prevent leaks.
- Material Selection:
- Seal Faces: Materials like carbon or ceramic must be chosen based on their compatibility with the sealed fluid to maintain effectiveness.
- Elastomers: Selection should consider their resistance to temperature and chemical properties of the fluid.
- Hardware:
- Corrosion Resistance: Metal components must resist corrosion to ensure longevity.
- Seal Flush System:Implementing an appropriate seal flush system is essential for maintaining cleanliness and cooling, extending the seal’s lifespan and ensuring stable operation.
FAQs
How Many Types Of Seals Are There In A Pump
There are several mech seal types used in pumps, including single seals, double seals, cartridge seals, and bellows seals.
Conclusion
To ensure the optimal performance and durability of your mechanical systems, carefully choose the appropriate mechanical seal based on your specific needs and conditions.
Explore the possibilities with our range of mechanical seals tailored for any application. Contact us today to find the perfect solution for your project, ensuring efficiency and safety in all your operations.
