Dry Gas Seals vs. Wet Seals: Key Differences

Mechanical seals play a crucial role in making sure that there is no leakage of gases or liquids in compressors and pumps. These seals are available in a number of types, with dry gas seals and wet gas seals being the two most popular ones. They are mainly used in the oil and gas industry, petrochemicals, and power generation sectors.

Apart from their distinctions, both of them have one common purpose ultimately, to ensure maximum efficiency and reliability of the system. Nonetheless, they are different in a number of ways and have some pros and cons in various applications. Knowing these differences is important and can help you choose the most appropriate type for your application requirements. Join us as we talk about both of them and their key differences in this article.

What are Dry Gas Seals? 

Dry gas seals are a type of non-contacting mechanical seal which are used to prevent gas leakage in compressors. Unlike traditional designs that rely on liquid lubrication, dry gas seals rely on a very thin film of gas, normally nitrogen or process gas, between the rotating and stationary faces. 

This separation reduces wear and allows the system to run efficiently. They are also cleaner, more reliable, and can be used in industries that are mainly concerned with efficiency and minimal maintenance since they can run without liquid or oil.

Features

• Operate using a controlled gas film instead of liquid

• Reduced friction due to non-contact design

• Compact and lightweight construction

• Require clean, dry, and filtered gas for reliability

• Generate less heat compared to liquid-lubricated seals

About 90% of new centrifugal compressors now come equipped with dry gas seals, signaling their strong preference over traditional wet seals. 

Pros of Dry Gas Seals

• Low energy consumption due to minimal friction

• Longer lifespan because of non-contact operation

• Lower maintenance costs compared to wet seals

• Cleaner operation, reducing contamination risks

• Efficient leakage control for high-speed compressors
  
  

Cons of Dry Gas Seals

• Higher initial cost than wet seals

• Require clean, filtered gas supply to work effectively

• Sensitive to contamination, which can shorten life

• Not suitable for all process conditions

Common Applications

Dry gas seals are most preferred for high-speed and high-pressure applications. They find extensive application in centrifugal compressors in oil and gas refineries, the petrochemical industry, natural gas distribution pipelines and power generation. Their high level of efficiency and reliability makes them a general solution to modern compressor systems.

Dry gas seals may need significantly less power than wet oil seals; up to 80% less power in some cases.

What are Wet Gas Seals?

Wet gas seals (also known as liquid-lubricated seals) are a more traditional sealing technology. Rather than using a gas, they have a thin layer of liquid, which may be oil or process fluid, to cool and lubricate the sealing faces. 

This liquid film also avoids leakage by forming a barrier under pressure. Wet seals are also commonly used in industries where liquid handling is not a problem and operating pressures are moderate.

Features

• Use a continuous liquid film for lubrication and sealing

• Provide natural cooling to seal faces

• More tolerant to contamination than dry gas seals

• Typically larger and heavier due to liquid management systems

• Simpler initial setup compared to gas seals

Pros of Wet Gas Seals

• Lower upfront cost compared to dry gas seals

• Proven technology with decades of industrial use

• More tolerant to contamination than dry seals

• Effective in moderate pressure applications

• Reliable cooling for seal faces due to liquid film
  
  

Cons of Wet Gas Seals

• Higher energy losses from friction

• Frequent maintenance required for liquid handling systems

• Leakage risk of sealing liquid into process streams

• Shorter seal life compared to dry gas seals

• Bulkier system, requiring more space

Common Applications

The wet gas seals are widely used in traditional compressor systems, moderate-pressure refining systems and chemical industry equipment. They can also be applied in pumps and compressors where a liquid supply is easy. Their relatively low cost makes them attractive where a project is under-budget; however, it's important to consider the long-term maintenance requirements.

Dry Gas Seals vs. Wet Gas Seals: Which one is right for you?

Each of these have its own benefits depending on the system design, operating conditions, and maintenance requirements. Choosing the right one is a matter of tradeoff between short-term financial costs, efficiency and long-term operational costs. Here is a side-by-side comparison:

Applications for Wet and Dry Gas Seals

While dry gas seals offer clear economic advantages in most applications, there are certain situations where wet gas seals are preferred. For example, if hazardous chemicals are used in the process, wet gas seals are more suitable. Wet gas seals trap hazardous gases in the oil, creating a barrier that prevents them from escaping into the atmosphere, while dry gas seals cannot effectively contain these gases. In this case, more pollutants are released into the environment.

Dry gas seals may also be unsuitable in certain situations. While dry gas seals are commonly used in pressure applications up to 1500 pounds per square inch (psi) (10,342.14 kPa) and are generally safe for use in compressors operating at 3000 psi (20,684.27 kPa), they may not be safe for use at higher pressures. Depending on the application and seal type, dry gas seals should not be used at temperatures above 300°F to 400°F (approximately 149°C to 204°C). In some cases, the design of the compressor makes retrofitting dry gas seals impractical.

Factors to consider when choosing

You can not just choose the cheapest option when deciding between dry gas seals and wet gas seals. The right opiton will depends on several factors like the working environment, the system design, as well as long-term objectives. The important considerations are:

Speed and Operating Pressure: Dry gas seals can be adapted to high pressure and high speed compressors, whereas wet seals can only work well when subjected to moderate conditions.

Initial Budget vs Lifecycle Cost: Wet seals are cheaper upfront, but dry seals can save money over the long-term due to reduced maintenance and energy savings.

Maintenance Resources: Dry seals have less frequent maintenance, whereas wet seals need frequent monitoring of liquid circulation systems.

Leakage Tolerance: If avoiding contamination is critical, dry gas seals provide cleaner operation with minimal leakage.

System Cleanliness: Dry seals must have clean and filtered gas; wet seals are more tolerant to impurities.

Where to buy Dry Gas Seal?

When you need high-quality dry gas seals, Lepu Seal provides a large selection of high-performance seals. The running gap for our dry seals varies 3 to 10 microns, suitable for different industries, and are durable, efficient, and easy to maintain.

 

Final Thoughts

So, which one should you choose? Its about choosing the one that is more suitable for your application. Dry gas seals can be particularly useful in high-speed, high-pressure applications where efficiency, long life, and clean operation are of important. On the other hand, wet gas seals continue to be popular due to their cheaper initial investment. 

Both of them are valuable for your system, but understanding their differences can help you avoid higher costs and downtime during the application.