What Is the Difference Between Single and Double Face Mechanical Seals?

Double Bellows seal

If you’re thinking about purchasing a high pressure gas compressor from Ro-Flo for your application, you’ve likely noticed that we offer two options for the shaft seals: single face mechanical or double bellows. Single face mechanical seals are valued for their simple, robust design that is easily repaired in the field, while double bellows seals offer unparalleled protection. Here’s the difference between single and double bellows mechanical seals and the best applications for each type.


Single Face Mechanical Seals

While the concept of a seal is straightforward, in a machine like a rotary sliding vane compressor, the execution is more complex. Single face mechanical seals are made by using a spring to press together two flat surfaces, which slide against each other. A fluid film created from the lube oil forms between the two flat surfaces, creating a barrier and reducing wear.

The most common problems with single face mechanical seals involve the quality or quantity of the lubrication oil, an accumulation of debris between the sealing faces, and damage to the sealing faces or O-rings. These issues are all easy to diagnose and repair on-site. This simplicity makes single face mechanical seals the preferred option in many applications.


Double Bellows Mechanical Seals

This type of seal is precisely what it sounds like: two mechanical seals arranged either back-to-back or face-to-face. When combined with a seal support system, a double bellows seal reduces emissions to nearly zero.

The seal setup involves one or two seals per compressor, depending on the shaft configuration. An oil reservoir completes the system; for best results, each seal should have its own reservoir with one gallon of oil per inch of shaft diameter. If your compressor is used in cold weather applications, an oil heating system may be needed in the reservoir to regulate viscosity.

To operate a compressor with a double bellows seal, the seal cage needs to be filled with oil and pressurized with buffer gas prior to operation. The seal system must be pressurized prior to pressure testing the process gas piping system or running the compressor. If the process gas system is pressurized prior to the seal being pressurized, the seal is likely to fail.

Double bellows mechanical seals are used for any application in which the vapors are harmful to people and the environment. Often, this type of seal is stipulated by safety and environmental regulations. Because many of our clients are in the oil and gas industry or managing biogas, this type of seal is recommended. That said, if you’re uncertain which type of seal is the correct one for your application, our engineering team can help you decide.


Learn More About Ro-Flo High Pressure Gas Compressors

While there are many types of compressors on the market, we believe rotary sliding vane compressors are a step above the rest. Find out why by contacting Ro-Flo today at (920) 574-2652 to learn more about our products and their applications, or email tsixel@ro-flo.com.