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Mechanical Seal vs Dry Gas Seal

Mechanical seals and dry gas seals are both used to prevent leakage in rotating equipment.

However, they have distinct differences in their design, operation, and application.

In this blog post, we’ll explore these differences in detail, helping you make an informed decision when selecting the right seal for your specific needs.

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The Difference Between Mechanical Seal and Dry Gas Seal

Lubrication:

Mechanical seals: Mechanical seals typically use a liquid film, such as oil or the process fluid itself, to lubricate the seal faces and prevent leakage. The seal faces make physical contact and the liquid helps reduce friction and wear.

Dry gas seals: Dry gas seals use a pressurized gas, such as nitrogen or clean process gas, to create a thin gap between the seal faces. The faces do not make contact and the gas acts as a lubricating and sealing medium. This eliminates the need for liquid lubrication.

Seal design:

Mechanical seals: Mechanical seals consist of a stationary ring and a rotating ring with very flat, precision lapped faces. Springs or bellows are used to maintain contact between the faces. Secondary seals like O-rings are used to prevent leakage between the rings and the shaft or housing.

Dry gas seals: Dry gas seals have a rotating ring with spiral grooves etched on the surface. When gas is pumped between the faces, it creates a high pressure film that separates the faces by a small gap, typically a few microns. This allows the faces to run without contact or wear.

Applications:

Mechanical seals: Mechanical seals are very versatile and can handle a wide range of liquids, temperatures and pressures. They are commonly used in pumps, mixers, and other rotating equipment.

Dry gas seals: Dry gas seals are mainly used to seal lighter gases in high speed compressors and turbo-machinery. They are preferred for sealing flammable or toxic gases where liquid contamination must be avoided. Dry gas seals can handle very high pressures and speeds but are more sensitive to solid particles and liquids in the gas stream.

Leakage:

Mechanical seals: Mechanical seals are designed to minimize leakage but will always leak some liquid due to the lubricating film between the faces. Typical leak rates are a few milliliters per hour.

Dry gas seals: Dry gas seals leak a small amount of gas instead of liquid. A typical tandem dry gas seal will leak 1-6 standard cubic feet per minute of gas. Most of this leakage is the clean sealing gas supplied between the seal faces.

Auxiliary systems:

Mechanical seals: Mechanical seals often require complex seal support systems to provide clean barrier fluid, cooling and leakage collection. API piping plans define various standard configurations.

Dry gas seals: Dry gas seals require a clean, dry sealing gas supply at a pressure higher than the process. This is usually taken from the compressor discharge and passed through filters and regulators. A typical system is API Plan 74.

Costs

Mechanical seals: Mechanical seals are simpler and less expensive to purchase and install initially.. Mechanical seals require seal flush fluid that is wasted, adding to operating costs over time.

Dry gas seals: Despite their higher initial cost, dry gas seals can provide operating cost savings over time. Dry gas seals have lower power consumption, using around 5 kW per hour vs 50-100 kW for wet seals. This adds up to significant energy savings.

Maintenance Requirements

Mechanical seals: Mechanical seals require constant attention and adjustment to maintain proper leakage rates and prevent overheating damage. Routine maintenance is needed throughout the life of the seal.

Dry gas seals: Dry gas seals are non-contacting and self-adjusting. When operating properly, they do not wear and require no regular maintenance interventions. However, when dry gas seals do have issues, the repair costs can be high due to their complexity. Damaged seal faces are harder to refurbish compared to simply replacing mechanical seal components.

FAQs

Is a Dry Gas Seal a Mechanical Seal

A dry gas seal is a type of mechanical seal that is specifically designed for sealing gases. Unlike other mechanical seals that use liquid lubrication, dry gas seals utilize the sealed gas itself as a barrier fluid to prevent leakage.

If the Pump Is Run Dry for a Few Seconds, Will It Damage the Mechanical Seal

Running a pump dry, even for just a few seconds, can potentially damage the mechanical seal.

This is because the seal relies on the pumped fluid for lubrication and cooling, and without it, the seal faces can quickly overheat and fail.

Conclusion

In conclusion, both mechanical seals and dry gas seals offer unique advantages for sealing rotating shafts.

Mechanical seals are versatile and cost-effective, while dry gas seals provide superior performance in high-pressure, high-speed applications.

Ultimately, the choice depends on your specific requirements and operating conditions.

Contact our experts today to discuss the best sealing solution for your needs.

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