Understanding Dry Gas Seals: Basic Structure, Working Principle & Usage

Dry gas seals (DGS) represent an important feature in modern industrial machinery, which helps compressors, turbines, and pumps to be free from leakage. While traditional seals require liquid lubrication, it uses a thin layer of gas to separate moving parts-with no real contact between them. 

Their operating capability with very expensive, toxic, or flammable gases stands out as the main advantage over traditional sealing methods. In this article, we will try to understand what dry gas seals are, their various types, their construction and operation, areas of application, common problems, and tips to keep them in perfect condition.Let's get started!

What is a Dry Gas Seal?

A Dry Gas Seal is a mechanical seal with which rotating and stationary parts in high-speed equipment are separated by a thin layer of gas. The wear and leakage are very negligible and are almost zero since there is no contact friction between the surfaces. 

Such types of seals are widely used in compressors, pumps, and gas turbines that require gas release to be managed. These seals have gained a reputation for their robustness with high speeds and pressures without any maintenance.

What Are the Different Types of Dry Gas Seals?

Dry gas seals are designed for various pressure levels, speed conditions, and safety requirements. Generally, there are single, double end, and tandem types. The right type would depend on the application conditions, gas characteristics, and operating environment.

Single Dry Gas Seal

The Single Dry Gas Seal has only one rotating and stationary face pair. It comes with a simpler design, that's why it's much cheaper. It can be used for low to medium pressures, and due to its simplicity, it also allows for easy installation and service. Thus, this seal type is suitable for the great majority of standard industrial compressors and pumps.

Double End Dry Gas Seal

The Double End Dry Gas Seal features two spots for the sealing surfaces that are opposite each other. This is ideal for applications that face either abrasive or aggressive gas. This type of gas seal is often utilized in high-speed, low-pressure operations such as hydrogen gas compressors or turbines.

Tandem Dry Gas Seal

Tandem Dry Gas Seal consists of two sealing surfaces in tandem. There is a buffer gas system between these surfaces. Such seals become desirable for high-pressure or critical services where redundancy and leak-tight integrity are of prime importance. 

They are often connected to a flare line for dealing with any slight leakages through a buffer gas system that is widely used in gas, petrochemical, or chemical processing units.

Dry gas seals are avalable in a variety of configurations (single, double opposed, and tandem) to suit all applications. Thetandem style seal configuration is the most common for process gas service.

*Seal design and component materials can be tailored to specific higher pressure applications or corrosive processes.

Basic Structure and Structural Characteristics of Dry Gas Seals

A dry gas seal typically consists of:

• Rotating Ring: Fitted to the shaft with grooves that generate a hydrodynamic gas film.

• Stationary Ring: Attached to the machine body, it is the primary seal area.

• Secondary Sealing Components: These include O-rings, gaskets, or backup rings that are used to.

• Buffer or Barrier Gas System:  Used in tandem machines and double end machines for enhanced safety.

These kinds of seals are precisely engineered using durable materials such as carbon, silicon carbide, or tungsten carbide to withstand high-speed and high-pressure operations.

Working Principle of Dry Gas Seal

Dry gas seals function on the principle of hydrodynamic lift. The rotation of the shaft directs gas across the seal faces through the grooves on the mating ring, creating a thin gas film. This film is responsible for keeping the rotating and stationary rings apart, avoiding actual contact. 

This is achieved through the non-contact face operation that ensures low friction, thereby allowing the seal to work at higher speeds with low leak rates.

Where Are Dry Gas Seals Commonly Used?

These gas dry seals are widely used in industries that need effective sealing with low gas leakage rates:

• Oil & Gas: Gas station dispensers, vapor recovery systems, tank gauges, fuel dispensing units commonly used these gas seals for effective and non-contact sealing. 
• Petrochemical & Chemical: High-pressure compressors, reactors, refineries are fitted with modular gas seals to ensure hygiene requirements.
• Power Generation: Gas and steam turbines, industrial generators.
• Industrial Applications: Hydrogen compression, Cryogenic Processes, Air separation units
  
  

These Seals work to minimize emissions, suppress contamination, as well as enhance efficiency.

Dry Gas Seal Troubleshooting Common Issues 

Even the best dry seals in the world can run into some issues. Here are some of them and how to solve them without excessive downtimes.

• Seal Leakage: This is primarily a result of improper sealing or worn-out O rings. Generally, checking for worn-out parts and replacing them, and proper alignment solves the problem.
• Excessive Heat: Either high speed of shafts or low gas supply causes this. Adjustments in operational speeds or gas flow rate restore normal operation.
• Seal Face Wear: The seal faces can be worn against a combination of abrasive and contaminated gases. The use of filters, clean gas, or upgrading to more durable materials like silicon carbide will prevent premature wear of the faces.
• Vibration: Misaligned shafts or unbalanced rotors can be responsible for improper wear. Realignment of the shaft and rotor balance assessment corrects the vibration issues.
• Unstable Operation: Variations in pressure, temperature, or gas flow could lead to performance deviation. The stability of operational conditions is a critical parameter that can ensure consistent sealing.

How to Maintain Dry Gas Seals

Following are some expert-vetted maintenance tips to keep the dry gas seals in perfect condition.

• Check for any damage or wear periodically.

• Make certain that the gas used is clean, dry, and free of contaminants.

• Tracking shaft speed, pressure, and temperature.

• Buffer or barrier gas systems, coolers, and instrumentation.

• Alignment and torque specifications must be followed as directed by the manufacturer for installation.

• Replace worn-out or damaged seals before failure occurs.

FAQs

1. Why are dry gas seals more reliable than traditional seals?

They are praised industry wide for their non-contact design, thereby minimizing friction, wear, and leakage. Traditional, liquid-lubricated seals can not match the reliable performance offered by most dry gas seals.

2. Which materials are ideal for dry gas seals?

These seals are made of carbon, silicon carbide, and tungsten carbide, each giving strength, chemical resistance, and temperature.

3. Can they handle extreme conditions?

Yes, the tandem and double-end designs withstand high pressure, temperature, and even aggressive gases.

4. How do they benefit the environment?

They reduce harmful emissions by minimizing gas leakage, thus improving overall safety.

5. How should they be maintained?

Most dry gas seals are low maintenance. All you need is some frequent inspections, a clean gas source, as well as monitoring of operational variables.

Conclusion

Dry gas seals are nowadays an essential part of almost every type of modern industrial machine. The reason is their unmatched benefits, including efficiency, reliability, and long life. Their non-contact design, with the least possibility of leakage, ensures they serve you well without extensive maintenance. This explains why most modern compressors, turbines, and pumps rely on them.

Choosing Reliable Dry Gas Seals Supplier

Lepu Seal is a trusted dry gas seal supplier offers quality dry gas seals to global clients. The total production workshop area exceeds 8000 square meters. That why we say our factory have strong production and supply capacity of mechanical seals, and can provide customers with good delivery services.

They provide a comprehensive range of dry gas mechanical seals designed to meet the reliability, safety, and performance requirements of specific applications. We continuously advance technology to meet the evolving needs of turbomachinery in the global energy industry. They  offer durable, reliable, and efficient dry gas seals for global industrial needs, focusing on uptime and cost reduction.