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Temperature:
Up to 400°C/750°F
■
Pressure:
Up to 27.6 bar g/400 psig
■
Speed:
Up to 122 m/s / 400 fps max.
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End Play/Axial Float Allowance:
±3.20mm/0.125"
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For Optimum Seal Performance:
Steam should have 28˚C to 56˚C/83˚F to 133˚F of superheat at inlet conditions.
■
For Optimum Seal Life:
Following a combination of NEMA Standard SM 24-1991 and EPRI guidelines for steam purity is strongly recommended. Consult John Crane for recommended steam purity limits.
P e r f o r m a n c e C a p a b i l i t i e s
D e s i g n F e a t u r e s
■
Bearing Oil Steam Contamination Dramatically Reduced
■
Increased Safety (reduced noise levels and hazards associated with leaking steam)
■
Standard Designs to Fit Most Single-Stage Turbines
■
Turbine Operational Efficiency Maintained for Years
■
Support Equipment Eliminated
■
Bi-Directional Face Patterns Available
28ST
P r o d u c t D e s c r i p t i o n
Type 28ST combines proven rotating groove technology and high-temperature secondary seals to reduce steam leakage by nearly two orders of magnitude, as compared to traditional sealing devices such as segmented carbon rings and labyrinths.
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This steam-lubricated, end-face cartridge seal reacts instantaneously and automatically to maintain a safe face gap despite sudden changes in operating conditions.
■
A stable seal face gap, typically 0.0025mm to 0.0051mm/
0.0001" to 0.0002", is the result of specially designed rotating grooves, which pump steam radially inward into a nongrooved portion of the seal known as the
“sealing dam.”
■
Primarily for use on steam turbines.
TYPE 28ST
Non-Contacting, Steam Turbine Gas Seal
A – Seat/Mating Ring B – Face/Primary Ring C – Split Carbon Ring
Assemblies
C B A Spiral Groove Face
Ty p e 2 8 S T Ty p i c a l A r r a n g e m e n t
The standard Type 28ST is designed to withstand speeds of 122 m/s / 400 fps max. and 1000 rpm min. (continuous). It is also slow roll tolerable. The Type 28ST is designed to fit most single-stage turbines without modifications. Standard designs exist for shaft sizes ranging from 25.4mm/1.000"
through 108mm/4.250" for most steam turbines, including:
Coppus, Dean Hill, Dresser Rand (Terry, Worthington), Elliott,
Hayward Tyler, KKK, Murray, Rateau, Spencer Turbine, and Tuthill Nadrowski models. Larger, nonstandard sizes are available. Consult John Crane for your specific application.
The Type 28ST has an excellent track record in the most demanding steam turbine applications.
Ty p e 2 8 S T A p p l i c a t i o n s D a t a
Bearing Side
Steam Chest Side
28ST TYPE 28ST
Non-Contacting, Steam Turbine Gas Seal
Obtaining Optimum Performance
Steam purity (cleanliness) and steam quality (percent vapor) are probably the two most critical ingredients in achieving optimum performance from your steam turbine and your Type 28ST seal. John Crane suggests following a combination of the National Electrical Manufacturers’ Association (NEMA) and the Electric Power Research Institute (EPRI) guidelines for steam purity limits for improved reliability of not only the Type 28ST seals, but also the entire steam turbine.
Consult John Crane for recommended steam purity limits. See chart at left for recommended steam quality operating conditions.
R e c o m m e n d e d M i n i m u m I n l e t Te m p e r a t u r e v s . I n l e t P r e s s u r e
600 550 500 450 400 350 300
50 150 250 350 450 550 650 700 (psig)
Inlet Pressure
(bar g)
0 10 20 30 40 50
Temperature °F Temperature °C
300
250
200
150
TYPE 28ST
Non-Contacting, Steam Turbine Gas Seal Ty p e 2 8 S T Ty p i c a l L e a k a g e C h a r t *
C o n v e n t i o n a l S e g m e n t e d C a r b o n R i n g s Ty p i c a l L e a k a g e C h a r t *
7 6 5 4 3 2 1
0 0 50 100 150 200 250 300 (psig)
Pressure
(bar g) 5
0 10 15 20
Steam Leakage (lbs./hr.)
250 200 150 100 50 0
Steam Leakage (lbs./hr.)
0 50 100 150 200 250 300 (psig)
Pressure
(bar g) 5
0 10 15 20
*Based on an 88.9mm/3.500" shaft diameter.
■Steam contamination of bearing oil virtually eliminated.
■Rust and corrosion of other equipment dramatically reduced.
Ty p e 2 8 S T C o s t S a v i n g s v s . Tr a d i t i o n a l S e a l s *
250 200 150 100 50 0
Steam Leakage (lbs./hr.)
0 50 100 150 200 250 300 (psig)
Pressure
Traditional Seal
Type 28ST
(bar g) 5
0 10 15 20
COST SAVINGS
North and Latin Americas Morton Grove, Illinois USA Tel: 1-847-967-2400 Fax: 1-847-967-3915 1-800-SEALING
Europe, Middle East, Africa Slough, UK
Tel: 44-1753-224000 Fax: 44-1753-224224
Asia Pacific Singapore Tel: 65-222-9161 Fax: 65-223-5035
For your nearest John Crane facility, please contact one of the locations above.
If the products featured will be used in a potentially dangerous and/or hazardous process, your John Crane representative should be consulted prior to their selection and use.
In the interest of continuous development, John Crane Companies reserve the right to alter designs and specifications without prior notice. It is dangerous to smoke while handling products made from PTFE. Old and new PTFE products must not be incinerated.
©1999 John Crane Print 11/99 www.johncrane.com ISO Certified S-28ST
John Crane
TYPE 28ST
Non-Contacting, Steam Turbine Gas Seal
M a t e r i a l s o f C o n s t r u c t i o n
SEAL COMPONENTS MATERIALS Description Standard Face/Primary Ring Carbon
Seat/Mating Ring Tungsten Carbide
Coatings on Ductile Substrates Secondary Seals Carbon/Inconel®
Flexible Graphite
Hardware 410 Stainless Steel
Springs Inconel®X-750
Fasteners Zinc-Coated Hardened Steel Inconel is a registered trademark of Inco Alloys International, Inc.