The carbon ring seal is a non-contact floating seal and a type of floating ring seal. Its sealing principle is based on the formation of a gas film between the carbon ring and the shaft sleeve. This gas film creates a throttling effect and gradually reduces the pressure, thereby preventing medium from leaking. The following sections describe its structure, operating principle, advantages, applications, and technology trends.
1. Structure
Main Components
- Seal Housing – Accommodates the sealing assembly and provides installation space.
- Shaft Sleeve – The sleeve surface is coated with wear-resistant materials such as aluminum oxide (Al₂O₃), chromium oxide (Cr₂O₃), or silicon carbide (SiC) to protect the rotating shaft and minimize wear.
- Carbon Rings – Rectangular cross-section sealing rings, typically installed in series with at least two rings. A controlled radial clearance of approximately 3–10 μm per side between the carbon ring and the shaft sleeve ensures effective sealing.
Structural Configurations
By Assembly Type
Split type (easy maintenance)
Integrated (non-split) type
By Installation Location
Internal type
External type
By Operating Condition
Gas-buffered design
Oil-buffered design
Non-buffered design
2. Operating Principle
Gas Film
The gas, typically nitrogen, is introduced as a buffer gas to form a stable gas film between the carbon ring and the shaft sleeve. The gas film provides a throttling effect that gradually reduces pressure and isolates the high-pressure medium.
Self-Centering
During operation, the gas film pressure causes the carbon ring to float automatically and align concentrically with the rotating shaft, minimizing wear. Under static conditions, O-rings, springs, or retaining springs position the carbon ring and reduce shaft eccentricity.
Sealing
Multiple carbon rings are installed in tandem. The fluid passes through successive throttling stages, resulting in gradual pressure reduction and highly effective sealing performance.
3. Advantages and Limitations
Advantages
- Simple structure with easy maintenance
- Low maintenance costs
- No complicated lubrication or cooling system required
- Excellent corrosion resistance and compatibility with various process media
- Suitable for a wide range of industrial applications
Limitations
- Leakage exists in non-buffered configurations
- Self-lubricating performance decreases at very low temperatures, reducing sealing efficiency
- High-speed and high-pressure operation may increase shaft wear
4. Applications
Typical Equipment
- Steam turbines
- Fans and blowers
- Generators
- Compressors
- Turbines and turbo-expanders
- Centrifugal pumps
- Screw pumps
- Compressor crankshafts and rotor shafts
Operating Conditions
- Temperature: -120°C to +500°C (special attention should be given to reduced self-lubrication at extremely low temperatures)
- Pressure: Up to 30 MPa, with multiple carbon rings for high-pressure applications
- Media: Air, nitrogen, carbon dioxide, ammonia, and various flammable, explosive, toxic, or hazardous gases
Special Applications
When sealing flammable, explosive, or toxic gases, nitrogen is commonly introduced as a buffer gas to achieve near-zero emissions or ensure safe venting. Carbon ring seals are widely used in the petroleum, chemical, metallurgical, pharmaceutical, food processing, and power generation industries.
5. Technology Trends
Advanced Materials
Carbon fiber-reinforced graphite composite materials are increasingly used to reduce thermal expansion and extend service life.
Precision Manufacturing
Modern precision machining is replacing traditional manual lapping, significantly improving the dimensional accuracy and consistency of carbon rings.
Customized Designs
Manufacturers increasingly provide customized solutions, including split-type designs, automatic compensation structures, and other application-specific configurations to meet different operating requirements.
Representative Manufacturer
Chengdu Novseal Technology Co., Ltd. specializes in the research, development, and manufacturing of carbon sealing products. Its products are widely used in the power generation, metallurgy, petrochemical, and other industrial sectors, serving more than 300 customers worldwide.