Apr 18, 2023 Flowserve Sanmar Limited
Typical Centrifugal Pump
1. Suction 2. Impeller 3. Discharge 4. Stationary casing 5. Shaft6. Mechanical Seal 7. Gland 8. Bearings
Apr 18, 2023 Flowserve Sanmar Limited
Stuffing Box Pressure• The pressure acting on the stuffing box which
must be sealed.• It is a function of pump impeller design and the
presence or condition of wear rings.• Impeller design and Stuffing box pressure
– Back vanes - Open impeller• Suction + 25% of differential = Stuffing box pressure
– Balance Holes - Closed impeller• Suction + 10% of differential = Stuffing box pressure
– Double Suction• Suction pressure = stuffing box pressure
Apr 18, 2023 Flowserve Sanmar Limited
Viscosity – Generally the higher the viscosity, the better the lubricating
characteristics
– A product with a viscosity of 20,000 SSU (5000 cp) can be sealed with standard seals
– Beyond 5000 cp, the drive unit has to be beefed up to compensate for the increased shear occurring at the sealing faces.
– For high viscous applications:
• Single seal with external flush
• Double seal with external flush
– The viscosity & lubricity of water decrease with increased temperature. Above 82C (viscosity 0.35 cp) seal faces can contact each other and wear rapidly, unless specially designed
Apr 18, 2023 Flowserve Sanmar Limited
Specific Gravity – Specific Gravity = Density of a substance
Density of Water at 4C– Specific gravity is used to estimate the lubricity of
light hydrocarbons– Specific gravity below 0.68 (Heptane), require one
face as carbon and special seal face design with higher balance to contain fugitive emissions
Apr 18, 2023 Flowserve Sanmar Limited
Vapour Pressure – The pressure at which a liquid will flash into vapor at
given temperature– If seal generated heat causes the sealing liquid to boil
in seal chamber pressure, the liquid film between the seal faces will vaporize.
– Solution :• Increase seal chamber pressure with proper bypass flush
line and throat restriction device.
• Cooling the seal chamber. Seal chamber should be kept at least 15C below the boiling point of the product at the seal chamber pressure
Apr 18, 2023 Flowserve Sanmar Limited
Cavitation – Operated under cavitating conditions for sufficient length of
time:• Pitting of impeller vanes and pump volute
• Short bearing life and heavy loading
• Shaft breakage and other fatigue failures in the pump
• Short seal life
– Damages to mechanical seals can be :• worn pins and pin slots
• Broken springs
• shaft fretting
• Chipping of carbon faces
Apr 18, 2023 Flowserve Sanmar Limited
Cavitation – High speed video shows that seal face temperature excursions occurred when
gases were drawn across the seal faces and by the formation of gas bubbles in the seal chamber near the seal faces during pump cavitation.
Seal Performance during cavitation :
Zones Normal PumpOperation
Pump CavitationMode
Seal chambertemperature (C)
65 65
Shaft sleevevibration, mils p-p
1.9 2 to 8.4
Seal facevibration, mils p-p
<2.0 13 to 35
Seal facetemperature ( C )
67 to 74 166 to 427
Apr 18, 2023 Flowserve Sanmar Limited
Vibration – Pusher Seals :
• Vibration should be kept below 0.32 inches/second
• At levels beyond 0.32 inches/second and upto 0.60 inches/second seal damage and leakage will start.
– Bellows seals :• Axial vibration of the bellows seal end face
– Caused by out of perpendicularity
– Dampened by the hydraulic closing force
• Axial vibration of the bellows leaflets– Caused by the vibration of the
• Stick-slip torsional vibration
• Radial vibration of the bellows seal face end piece
Apr 18, 2023 Flowserve Sanmar Limited
Typical Stuffing Box with compression packings
ImpellerStuffing BoxPacking Pusher
Fasteners
Compression Packings
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Disadvantages of Compression Packings
Power consumption is HIGH. The ratio of power consumptionof Mechanical Seal to compression packing is 1:8
Leakage is very high and unpredictable. Varies with compressionon the packings. The ratio of Leakage of mechanical seal to compression packing is 1:600No automatic wear compensation
Fretting on sleeve or shaft
Apr 18, 2023 Flowserve Sanmar Limited
Typical Unbalanced Seal
Compression Unit
Collar
Set screwSprings Drive Pin Gland
Insert Mounting
Insert
SealringShaft Packing
Compression ring
Hardwares: Collar, Compression ring, Gland, SleeveSeal Faces : Sealring & InsertSecondary Packings : Shaft packing, Insert Mounting, Sleeve &Gland Gaskets
Apr 18, 2023 Flowserve Sanmar Limited
5 Paths of LeakageGland Gasket
Shaft Packingand Sleeve
Shaft Packingand Sealring
Insert Mounting
Seal Faces
Apr 18, 2023 Flowserve Sanmar Limited
Materials : Hardwares
• 300 series Stainless Steel like 316ss, 316Lss
• 400 series Stainless Steel like 410ss
• Duplex Stainless Steel
• Alloy 20
• Hastalloy B & C
• Monel
• Inconel
• Nickel
• Titanium
Apr 18, 2023 Flowserve Sanmar Limited
Materials : Seal Faces
• Carbons :– # 5 Carbon (273C)– #17 Carbon (320 C)– Antimony Impregnated Carbon (204 C)– #18 Carbon (Salt Impregnated - SB 200 only)– Special Grades
Apr 18, 2023 Flowserve Sanmar Limited
Materials : Seal Faces
• Tungsten Carbide :– TungCar 62-6 (Ni bonded) - 400 C– TungCar 62-1 (Cobalt bonded) - 400 C
• Silicon Carbide :– Silicon Carbide 1(Reaction bonded) - 427 C– Silicon Carbide 2 ( - Sintered) - 427 C
Apr 18, 2023 Flowserve Sanmar Limited
Materials : Seal Faces
• Peramic :– Pure Aluminum Oxide - 177 C
• Weak in Thermal shock
• Good Chemical resistance
• Durchrome – Chromic Oxide layer on metal body - 177 C
• Glass Filled Duraflon– in TB seals
• Temperature limit of 71C as seal face
Apr 18, 2023 Flowserve Sanmar Limited
Shaft Packings
Viton - 204CNeoprene - 107CBuna N - 107CEPR /EPT - 177CKalrez - 315C
Pure Teflon - 177CGlass Filled Teflon - 232CTeflon Encap. “O” ring - 204C
Fully Interchangeable Shaft Packings
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