19-06 SEAL APPLICATION OUTLINE

SEAL MATERIALS

 UNFILLED CARBON/ GRAPHITE 

• The ideal soft face material
• Do not use with:
• Oxidizers or halogens
• Color contamination problems
• Hot oil – possible pitting
• Deionized water. Carbon was often removed during the process

HARD FACES

• Alpha sintered silicon carbide - no small cross section pieces
• Reaction bonded silicon carbide – do not use in high pH fluids
• 99.5 Ceramic - No hot oil or water
• Nickel TC - Possible galvanic corrosion with stainless steel
• Cobalt TC - Not as corrosion resistant as nickel tungsten carbide

FACE COMBINATIONS

• Unfilled carbon/Alpha sintered – For most application
• Unfilled carbon/99.5 – Avoid in hot oil or hot resin applications
• Alpha sintered/ nickel TC – Good in hot oil, abrasive slurry
• Alpha sintered/ reaction bonded – An alternative hard face

ELASTOMERS- Use the four step procedure to select the correct one for your application:

• Look in an elastomer book. Watch out for flush fluids that are not compatible with the elastomer
• Consider temperature limits of the elastomer
• Look for elastomer experience in your plant for compounds and fluid mixtures that are not in the book.
• Valves
• Other seals
• Gages
• Covers
• Flanges
• Test for compatibility
• Immerse in the fluid for 1 to 2 weeks
• Look for change in weight, shape, appearance
• Chemraz or Kalrez is a high priced alternative. Do not use Chemraz in high pH fluids
• Miscellaneous elastomer problems:
• Ethylene oxide blows out particles of the elastomer
• Buna, shelf life (Subject to ozone attack)
• EPR – not compatible with petroleum products.
• Viton – possible compatibility with water problem

METAL COMPONENTS EXPOSED TO THE SEALING FLUID

• Choose same metal as wet end of the pump, if not corroding.
• Iron, steel, SS or bronze wetted parts, can probably use 316
• Hastelloy “C” for seal springs and bellows to prevent chloride stress corrosion problems
• Non metallic pump - use non metallic seal design

ENVIRONMENTAL CONTROLS

CONTROL TEMPERATURE IN THE SEAL AREA

• Jacket on pump – circulating condensate or steam
• Quench gland
• Watch out for bearing contamination
• Dual seals - avoid oil as a barrier or buffer fluid because of its low specific heat and conductivity
• Place a pumping ring in stuffing box
• Heat exchanger - only works while pump is running. Clogs easily
• Flush with liquid at the correct temperature - 15 lbs (1 atmosphere). higher than stuffing box pressure
• Water
• Compatible fluid
• One of the ingredients
• Finished product
• Additive
• Heat tape around the stuffing box.
• Build a dog house over the pump with a steam line inserted to heat the contents     

CONTROL THE PRESSURE IN THE STUFFING BOX

• Discharge recirculation to increase pressure. Use a restrictive bushing in bottom of the stuffing box.
• Suction recirculation to lower pressure
• Cross connect stuffing boxes in a double ended pump
• Dual seals with a pressurized barrier fluid

REPLACE THE FLUID IN STUFFING BOX

• Suction recirculation to remove solids.
• Large stuffing box to centrifuge the fluid
• No tapered designs
• Pressurized barrier fluid
• Flush with a compatible liquid
• Water
• Compatible fluid
• One of the ingredients
• Finished product
• Additive that will be inserted down stream.
• Grease for slow speed applications
• Pump back seal

SEAL APPLICATIONS

FLUIDS SENSITIVE TO TEMPERATURE AND PRESSURE CHANGES’
They can:

• Build a film on the seal sliding components and between the lapped faces
• Change viscosity
• Crystallize
• Increase corrosion
• Solidify
• Vaporize

FLUIDS SENSITIVE TO AGGITATION

• Dilatant - thickens
• Newtonian - doesn’t change
• Pseudo-plastic – change viscosity suddenly
• Thixothrophic – thins out

SLURRIES
In slurry applications do any of the following:

• Large bore stuffing box – not tapered
• Suction recirculation
• Flush with a compatible liquid using a restrictive bushing
• Grease for slow applications
• Pump back seal
• What does not work:
• Filter/strainer in the pump discharge recirculation line
• Cyclone separator
• Back to back dual seals with a clean liquid between them
• Two hard faces
• Mount outside to keep the springs out of the slurry

NON-LUBRICANTS

• Non lubricating liquids (includes most solvents)
• Use dual seals with a barrier fluid
• Gases
• Use dual seals with a barrier fluid
• Dry solids
• Use centrifugal force to throw the solids away from the sliding seal components
• Blowing a gas in does not work. It channels through the solids

USE DUAL SEALS WITH:

Type of fluid:

• Dangerous
• Fire hazard
• Toxic
• Carcinogen
• Explosive
• Radiation
• Pollutant
• Must conform to the Clean Air Act
• Fugitive emissions
• Expensive products
• Back up for predictive maintenance

FLUIDS THAT COMBINE TOGETHER TO FORM A SOLID

• Usually mixed outside pump
• Flush pump with tank cleaning liquid

CLEAN LUBRICATING LIQUIDS

• No problem

EXTREME OPERATING CONDITIONS

TOO HOT FOR THE SEALING FLUID OR A SEAL COMPONENT

• Metal bellows for non-coking fluids
• Cool the product in the stuffing box
• Problems when pump is not running:
• Soak temperature
• You must protect the bearings

CRYOGENIC FLUIDS

• Metal bellows
• Special carbon/ graphite containing an organic to release the graphite
• Isolate moisture outboard, or it will freeze restricting movement of the seal

HIGH PRESSURE IN THE STUFFING BOX. >400psi or 27.5 bar

• Seal face distortion
• Increase mass
• Use finite element analysis techniques in design
• Face load
• Hydraulic balance essential
• Extrude dynamic elastomer
• Higher durometer elastomer
• Back up rings
• Metal bellows
• Thicker plates
• Laminated plates

HARD VACUUM (less than 0.001 Torr)

• Elastomer can “out gas” and leak
• Non elastomer bellows
• Face leakage
• Prevent distortion with finite element analysis
• Self-align cartridge seal design to prevent excessive axial movement
• Stationary design non-cartridge seals
• High density carbon/ graphite seal face

HIGH SPEED

• Stationary seal design
• Lower face load
• Low friction faces
• No elastomers in face
• Move close to bearings

EXCESSIVE MOTION

• Wide hard face
• Increase internal clearances
• Locate the seal close to bearings

EXCESSIVE VIBRATION

• Sources of vibration:
• Harmonic
• Out of balance
• Slipstick
• Use vibration damping
• O-ring is a good damper
• Metal bellows designs need a damper device

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