1. FUNDAMENTALS OF MECHANICAL SEAL
Author
Prem Baboo
Sr. manager(Prod)
National Fertilizers Ltd,India
F.I.E. Institution of Engineers India,
Technical Advisor & an Expert for

2. FUNDAMENTALS OF MECHANICAL SEAL OPRATION
The liquid to be pumped enters the suction inlet at the eye of the impeller.As the impeller rotates at relatively high speed .The liquid centrifugally forced to the out side diameter of the impeller where it flows out through the discharge nozzle. This same discharge pressure, however, flow down behind the impeller to the drive shaft which is connected to a driver out side the pump. This is the shaft that must be efficiently sealed if the pump is to be of any practical use.
Relieving the high pressure behind the impeller to the low pressure suction eye of the impeller. The clearance between the back of the impeller and the pump back head actually much closer. Small pumping vanes are often placed on the back side of the impeller. Balance hole can also be drilled through the suction eye.
By decreasing the pressure differential between front & rear of the impeller. This also reduce axial thrust on the shaft. So the suction pressure, plus small percentage of discharge pressure always surround the drive shaft.

3. Stuffing box with compression pkg.
I f t h i s p k g . W e r e t o r u b a g a i n s t t h e s h a f t , w i t h o u t l u b r i c a t i o n p r e s e n t t o p r e v e n t a b u i l d - u p o f f r i c t i o n a l h e a t , i t w o u l d s o o n d e s t r o y i t s e l f . S o l i q u i d m u s t b e a l l o w e d t o f l o w b e t w e e n t h e p k g . a n d s h a f t , b e c a u s e o f s u r f a c e i r r e g u l a r i t i e s o f p k g . , e c c e n t r i c i t y b e t w e e n t h e s t u f f i n g b o x b o r e a n d t h e s h a f t , a s w e l l a s s h a f t r u n o u t a s i g n i f i c a n t a m o u n t o f p k g . M u s t b e u s e d t o c o m p e n s a t e f o r t h e s e i r r e g u l a r i t i e s . I t i s t h i s g e n e r o u s a m o u n t o f p k g . t h a t r e q u i r e s a p r o p o r t i o n a t e l y g e n e r o u s a m o u n t o f l u b r i c a t i o n . W h e n t h i s f l o w o f l u b r i c a t i o n e x i t f r o m t h e p k g . i t b e c o m e s i d e n t i f i e d a s l e a k a g e .
Stuffing box with compression pkg.

4. Introduction-. Mechanical seal
In modern process / chemical industries where highly corrosive and expensive fluid are handled. Leaks are not tolerated. Since soft packing works on the principle of controlled leakage. The system is not accepted, hence mechanical seal preferred as they tend to seal with no visible leak. .

5. Function of mechanical seal
The function of every mechanical seal is to prevent.The escape of a fluid.The clearance between rotating shaft and the passage way through the wall of a housing /casing or pressure vessel.

6. Three primary sealing points
1) Between stationary element and casing
2) Between rotating element and shaft
3)Between mating surfaces of the rotating and seal elements

7. Three basic components
A set of primary sealing element
A set of secondary sealing element
Hardware for attaching,positioning and maintaining face to face contact

8. Primary sealing element
It is formed by two highly polished /lapped faces.
One face is kept stationary and other face is fixed to a rotating shaft.
(That create very difficult leakage due to rubbing contact between them.all seals leak but leakage is not visible.the leakage is very small and non hazardous).

9. Secondary sealing element
Leakage path around stationary and rotating face are closed by secondary seals.
The secondary seals are made up of various fluro-castomers.
For pusher type of seals must move forward along the shaft to compensate for wear and vibrations at the seal faces.
For non pusher type seals such as T metal bellows,wear are taken internally and secondary seals are truly static.

10. Hardware
Adapt seal to various pieces of equipment. This hardware consist of a sleeve or housing to make for an easier more precise seal setting.
Provides mechanical pre-loads to seal faces until hydraulic pressure can take over. This is largely accomplished by a large single coil spring or by a set of small coil spring.
Transmit torque to both stationary and seal faces. Drive pins,dents, notches or screws incorporated into the seal design.

11. Gland plate
Pump body
sleeve
Sleeve gkt.
shaft
Reference line

12. MECH. SEAL PUMP BODY GLAND BOX IMPELLER
Fluid Pr. B
IMPELLER
(Hydrostatic Pr.+Hydrodynamic Pr.) P`
CLOSING FORCE=P*AREA(A-C)+SPRING FORCE
OPENING FORCE=P`*AREA B

13. INSIDE UNBALANCED SEAL
STUFFING BOX PRESSURE
ALL THE PRESSURE ON THE SEALIS NOT TRYING TO PUSHTHE SEAL RING TO THE ATMOSPHERIC SIDE OF STUFFING BOX
ATMOSPHERIC PRESSURE
OPENING FORCE
CLOSING FORCE
FOR PR. UP TO 20 Kg/Cm2 13

14. INSIDE BALANCED SEAL FOR PR. UP TO 40 Kg/Cm2 STUFFING BOX PRESSURE
ATMOSPHERIC PRESSURE
OPENING FORCE
CLOSING FORCE
FOR PR. UP TO 40 Kg/Cm2

15. OUTSIDE BALANCED SEAL Closing force Opening force
ATMOSPHERIC PRESSURE
Closing force
Opening force
FOR PR. UPTO 27 Kg/Cm2

16. FUNDAMENTAL SEAL DESIGNS
MECHANICAL SEAL WITH MULTIPLE SPRINGS
SINGLE COIL SPRING SEAL
Gland Gkt.
Pump body
Gland ring
Insert mounting
Compression unit
insert
Seal ring
Shaft pkg.
Spring
Drive pin
Compression ring
Springs
Collar
Set screws

17. FUNDAMENTAL SEAL DESIGNS
M E T A L B E L L O W S S E A L
FUNDAMENTAL SEAL DESIGNS
ELASTOMER BELLOWS SEAL
Sealing point
Elastomer bellows

18. HIGH PRESSURE SEAL
FOR PR. UPTO 170 Kg/Cm2

19. HIGH SPEED SEAL
FOR PR. UPTO 80 Kg/Cm2

20. MECHANICAL SEAL ARRANGEMENTS
SINGLE OUT SIDE SEAL

21. DOUBLE INSIDE SEAL

22. DOUBLE TANDEM SEAL

23. DOUBLE INSIDE - OUTSIDE SEAL
INNER SEAL
OUTER SEAL
COMMON INSERT

24. INSTALATION OF SEAL
The following important point should be observed and strictly followed during seal installation.
Checked up- stuffing box face, axial movement of shaft,radial movement of shaft, shaft run out , stuffing box square ness, concentric of stuffing box bore and alignment and pipe strain .
Removed all burrs and sharp edges from the shaft or shaft sleeve.
Check the stuffing box bore and stuffing box face to insure they are clean and free from burrs.
All the seal assembly drawing gives the seal setting dimensions from the face of the stuffing box to the back of the rotary assembly.
Shaft or sleeve should be oiled lightly prior to seal assembly to allow the move freely over it.
Wipe seal faces clean and apply a clean oil film prior to complete the equipment assembly.
Complete the equipment assembly taking care when compressing the seal in to the stuffing box.

25. SEAL FACE MATERIAL COMBINATION
B r o n z e
N i - R e s i s t
C e r a m i c
T u n g s t e n C a r b i d e
F i l l e d T F E R e s i n s
S t e l l i t e
C e r a m i c ( p u r e A L 2 O 3 )
SEAL FACE MATERIAL COMBINATION
WATER
CARBON-GRAPHITE
TUNGSTEN CARBIDE
CAUSTICS

26. SEAL FACE MATERIAL COMBINATION
D u r a m a t e
S t e l l i t e
C e r a m i c
H e s t e l l o y
F i l l e d T F E R e s i n s
T u n g s t e n C a r b i d e
SEAL FACE MATERIAL COMBINATION
ACIDS
CARBON-GRAPHITE
CERAMIC
TUNGSTEN CARBIDE

27. SEAL FACE MATERIAL COMBINATION
C a s t I r o n
N i - R e s i s t
C e r a m i c
S t e l l i t e
D u r a m a t e
T u n g s t e n C a r b i d e
S i l i c o n C a r b i d e
SEAL FACE MATERIAL COMBINATION
OILS
CARBON-GRAPHITE
BRONZE
OXIDIZING FLUIDS
SILICON CARBIDE

28. MECHANICAL SEALS MATERIALS
Mechanical properties High modulus of elasticity High tensile strength Low coefficient of friction Excellent wear characteristics and hardness Self lubricating
Thermal properties Low coefficient of expansion High thermal conductivity Resistant to thermal shock Thermal stability
Chemical properties Corrosion resistant Good wetability and adhesive characteristics
ADDITIONAL
Dimensional stability
Good machinability & ease of manufacture
Economical and readily available

29. Composition (% of each element)
Material Cr Ni C Fe Si Mn S P Mo CU Co Cb Ti
N0H
304SS
18-20
8-12
.08
64-70 1 2
.03
.04 5
316SS
16-18
10-14
62-71
2-3
20SS 20 29
.07
44.18
.75 - 3
MONEL
63-70 .3
2.50 .5
.024
24-31 R
Hastelloy B 64
.12 5
.70
.80 28
Hastelloy C
16.50 53
.15 .8
W 4
2.5
Titanium
.10
.40
99.03
.5,.4,. 15
NICKEL 99
.05
Tantalum
Tant
99.81
.013
.027
.015
..20
W.01
.044
.012
.014,. 027,. 007

30. SECONDARY SEAL MATERIALS
ELASTOMERS “O”RINGS
Buna N- Excellent resistance to petroleum,temp.rang –40 oc to +107oc, not passes good resistance to ozone sunlight or weather.
Neoprene- Chloroprene rubber or synthetic rubbers, It continues used for refrigerant such as Freon & Ammonia, like Buna-n temperature rang –40 oC to +107oC
Butyl- Butyl rubber will resist the deteriorating effects many mild liquid , acetone but should not be used in petroleum. Temperature rang –40 oCto +107 oC
Silicone Rubber- Silicone elastomers are made from silicone, oxygen,hydrogen and carbon. Poor tensile strength tear and abrasion resistance. Temperature rang –62oCto +204oC
Viton- Fluorocarbon rubber , temp. ranging from –18oC to +204oC , it is applicable to petroleum oils diester base lubricants, silicon fluid, halogenated hydrocarbon water low temperature steam ,acids and many other fluids.

31. SECONDARY SEAL MATERIALS
“V” RINGS
Applied as a shaft pkg.The lips of two ring energized by the nose of compression ring then by forcing them into intimate contact with the O D of shaft and the shaft pkg.bore of the seal ring.
‘V’Ring applied as insert mounting. A spreader ring is used to press the lips of the ‘v’ ring against the O D of the insert and the gland ring bore.
Material TFE resin the trade name of teflon(duraflone) can be used in temperature –73 oC to +177 oC . In higher temperatures used glass filled Duraflon rang –115 oC to +232 oC

32. INTERCHANGEABILITY OF SECONDRY SEALS
SHAFT PKG. INTERCHANGEABILITY
INSERT MOUNTING INTER.
“o”ring
“v”ring
DURAFITE
DURAFITE
“O”RING
“V”RING
COVE RING

33. Mechanical seal start-up & operation
To make sure that seal faces are immersed in liquid.
All cooling lines heating lines should be operating and remain so far at least a short period after equipment is shut down.
Not to run the equipment dry while checking motor rotation.
The stuffing box should always be vented prior to start-up. Air may be entrapped in the top portion of stuffing box.

34. ENVIRONMENTAL CONTROLS
F L U S H I N G - B Y P A S S
C O O L I N G O R H E A T I N G
Q U E N C H I N G O U T S I D E & I N S I D E S E A L
ENVIRONMENTAL CONTROLS
TEMPERATURE CONTROL
The temperature surrounded the seal in a stuffing box is an extremely important consideration certain part of seal ,such as secondary pkg. & carbon may deteriorate under exposure to extremely high temp. viton below (204 0c) carbon break down above 260
These material must also be able to resist chemical attack by the liquid surrounding them. If often become necessary to protect same of materials by cooling the seal area.

35. ENVIRONMENTAL CONTROLS
FLUSHING
COOLING

36. ENVIRONMENTAL CONTROLS
The material being pumped solidifies at ambient temperature.(liquidity by heating )
Boiling point of the liquid in the stuffing box. The product must remain below its boiling point if it is to be pumped stuffing box can be heat traps.
Vaporization may also cause precipitation of salts minerals or other abrasive impurities.

37. FLUSHING- BY PASS
Introduction of a liquid in to a stuffing box at a higher pressure then stuffing box pressure.
When it is desired to use by pass flushing for cooling, inside & out side seal, a recirculation line is run from the discharge nozzle through a heat exchanger or with out heat exchanger, to a connection in the gland ring located over the seal faces.
Assuming that the product is dirty, a by pass flushing arrangement can be called upon to flood the stuffing box with clean liquid.
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