Type 28 Principles of OperationMating Ring

OUTER

DIAMETER

GROOVE DIAMETER

INNER DIAMETER

LAND

SPIRAL GROOVE

ROTATION RELATIVE TO PRIMARY RING

Type 28 Principles of OperationUni-Directional Spiral Groove

Gas is induced towards thecenter.

Gas is Compressed &Pressure increases toset Gap.Sealing Dam

Direction of Rotation

Type 28 Principles of Operation

Normal Operation　Approx. Gap = 0.003mm

Opening ForceClosing Force

Compression

Expansion

Spring Load

and Hydrostatics及び静圧効果

Reduced Gap

Increased Opening ForceClosing Force

Increased Gap

Closing ForceReducedOpening Force

Normal Operation

Closing Force Opening Force

Compression

Expansion

Approx. Gap = 0.003mm

Spring Loadand Hydrostatics

Analytical Tool

““CSTEDYCSTEDY”” (steady state) & (steady state) & ““CTRANSCTRANS”” (transient )(transient )

Type 28 Principles of OperationBi-Directional Spiral Groove

Gas is induced towards thecenter.

Gas is Compressed &Pressure increases toset Gap.

Sealing Dam

Direction of Rotation

Typical Tandem Arrangement

Ｎ2 Purge

Primary Vent

Application: Process Gas Compressors

Pressure: 125barG Temperature: -20 To +200℃Speed: 200m/Sec. Gases: All

Process Gas

Secondary Vent

Bearings

Filtered Process Gas

Operational GuidelinesGAS QUALITY:

• The gas quality feeding the seal should be clean and dry. This will provide an environment for optimum performance and longevity. It is generally recommended that a 2 micron (absolute) coalescing filter be incorporated in the seal supply gas line to prevent contamination from liquid and particles.

SEAL GAS SUPPLY FLOW: • The seal gas supply flow must be sufficient enough to

ensure that the seal is supplied with filtered gas during operation with the remainder going back into the compressor. This will provide an ideal sealing environment to maintain the optimum performance of the seals.

Operational Guidelines

LEAKAGE TRENDS:• Seal performance is monitored through leakage trends.

Occasional spikes in the leakage are no cause for alarm. Such spikes be a result of a process variation, shaft movement, pressure, temperature, and / or speed changes. A trend of leakage, however, may give forewarning of a seal problems. Please consult John Crane International if there are any concerns.

Operational Guidelines

REVERSE ROTATION: • Reverse rotation should be avoided at Uni-directional seal.

Short periods of reverse rotation of speeds less 1000 RPM can be tolerated, however, the seal may require refurbishment and should definitely be inspected after such a run.

REVERSE PRESSURE: • Reverse pressure under static conditions will result in an

increase in static leakage. Under dynamic conditions, reverse pressure can result in major damage to the seal components.

Operational Guidelines

LIQUID CONTAMINATION: • While the T28 Gas Seal is practically able to cope with

contamination from light liquids, it is basically not recommended to have contamination with liquids especially for bearing oil that is not recommended.

SLOW ROLL: • It is recommended that continuous speeds below 500 rpm

are avoided. This gives a wide safety margin over the speed at which a 3 micron running gap is achieved. It also provides an improved capability to cope with fluctuations within the machine as a stiffer fluid film is generated.

Operational Guidelines

TURNING GEAR: • Turning gear operation at speeds such as 5 - 12 rpm with

pressure on the system has not been detrimental to the gas seal. However, it is better to minimize duration to minimize potential wear.

DECOMPRESSION: • The gas seal decompression rate is typically

recommended at 8 bar/minute for the seal having elastomer O-rings for secondary seal locations. Faster decompression rates may be accommodated upon review of the specific application.

• For pressures lower than 30barG, not limit is applicable.

Operational GuidelinesVIBRATION:

• The gas seal has a relatively high tolerance level for vibration. It is capable of surviving vibration levels that exceed the machine's operating limits. Experience has shown gas seals to survive vibration levels of 100 microns peak to peak.

INSTALLATION:• Although the seals are robust in operation they can

easily be damaged by incorrect assembly, fitting or handling. It is therefore recommended that the seals are fitted by a EETC service engineer or John Crane International trained engineer.