What is mechanical seal and its types?
Mechanical seals are an essential aspect of various pumps and compressors across multiple industries. These seals come in different configurations, allowing them to be used in various application scenarios.
A mechanical seal is a device that connects the rotational shaft of a pump or compressor to its stationary housing or casing. The seal's purpose is to contain the pumped or compressed medium within the equipment's casing, preventing it from leaking out. Mechanical seals are common in high-pressure and high-speed applications where conventional gland packing can no longer function effectively.
Mechanical seals are not a one-size-fits-all type of component. Different types exist, each designed to serve a specific application purpose. This article focuses on mechanical seals' types, from the most basic to the most advanced.
Mechanical Seal Types
1. Single Mechanical Seal
The single mechanical seal is the most basic type of mechanical seal. It comprises two flat and smooth surfaces, one stationary and one rotating, pressed together under spring-loading. The seal faces come in different material types, such as ceramic, carbon, carbon graphite, and silicon carbide, among others.
Single mechanical seals are cheap and simple to use, making them the preferred type for small pumps or compressors, low-pressure systems, and non-corrosive applications. They have a limited lifespan, typically requiring regular replacement to maintain optimal performance.
2. Double Mechanical Seal
Double mechanical seals build on the single mechanical seal's design by incorporating an additional set of seal faces. The two sets of seal faces are separated by a barrier fluid or space. When the primary seal fails, the barrier fluid takes its place, preventing leakages.
Double mechanical seals offer better leakage protection and performance than single seals. They are suitable for high-pressure applications or where seal failure can lead to hazardous conditions such as explosions. Double seals are more expensive and complex to install and maintain than single seals.
3. Cartridge Type Mechanical Seal
A cartridge type mechanical seal incorporates a complete seal assembly into a single cartridge unit. The cartridge unit is pre-mounted and aligned, making it easy to install and replace.
Cartridge type mechanical seals reduce installation and maintenance time, as they require fewer steps than traditional seals. They are the preferred type for critical applications, as they are less prone to installation or assembly errors. Cartridge seals may come in single, double or tandem arrangements.
4. Balanced Mechanical Seal
The balanced mechanical seal type utilizes the pressure of the pumped or compressed medium to equalize the seal's face loads. The seal's balance ensures that the seal faces do not wear out too quickly, and it can handle higher pressure applications than unbalanced seals.
The balanced mechanical seal is more costly and complex than the unbalanced seals, but it offers better performance and longer lifespan.
5. Pusher Type Mechanical Seal
The pusher type mechanical seal consists of a set of elastomer bellows that compresses the seal's faces under spring-loading. The seal faces may come in different material types, including ceramic, carbon, and silicon carbide.
Pusher type mechanical seals offer better sealing against abrasive and corrosive fluids and are commonly used in chemical, petrochemical, and food processing industries.
Conclusion
Mechanical seals play a crucial role in ensuring equipment performance and preventing leakages. Different types of mechanical seals exist, catering to different application scenarios, including single mechanical seals, double mechanical seals, cartridge type mechanical seals, balanced mechanical seals, and pusher type mechanical seals.
When selecting a mechanical seal type, it is crucial to consider factors such as pressure, temperature, medium characteristics, and equipment operating conditions. Proper installation, maintenance, and replacement are necessary to get the best out of mechanical seals and to prevent equipment failures.
