Mechanical seals are important components for preventing leakage in centrifugal pumps. They provide dynamic sealing between the stationary housing and the rotating shaft. The three main types are gland packing, mechanical seals, and sealless pumps. Mechanical seals have permissible leakage rates and use balanced or unbalanced, pusher or non-pusher designs depending on the application. Proper selection involves considering the fluid, pressure, temperature, acceptable leakage rate, and other factors. Installation requires ensuring proper material compatibility and flatness of the seal faces.

1. Mechanical Seal :
Basic and Selection
Kirit Domadiya

2. Sealing and leakages
Static Sealing → Gasket, O ring
Dynamic Sealing → Gland packing, Mechanical Seal
Bearing housing sealing → Lip seal, Labyrinth, Bearing isolator

3. Poll Q 1 - Which is the most probable contributing
factor for majority of pump issue or failure ?
a.Bearing or lubrication
b.Mechanical Seal or seal plan
c.Impeller or wear ring
d.Shaft or Coupling

4. Mechanical Seal is a most important integral part of pump

5. Centrifugal Pump
Leakage path

6. Prevalent Dynamic Sealing methods
Source
:Sundyne
HMD
Gland packing, Normal leak 2-20 drops / minute Sealless pump – Zero leak
Pusher type Mechanical Seal Non-pusher type Mechanical Seal
Permissible
leakage 6 cc/hr
Or 1000 ppm
vapor

7. Leak paths
1.St. Box and Gland
2.Gland and mating ring
3.Sleeve and Mechanical Seal
4.Seal faces
Source : Flowserve

8. Seal face lubrication and Leakage Rate
(rough estimate)
Q →leakage rate in m3/sec
b → Face contact width in mm
h → gap height in μm
ΔP → pressure differential in Pa
η → dynamic viscosity in Pa·s
Source : Hydraulic Institute
Stable liquid lube film must be
maintained between the seal faces
at all the times.

9. Face flatness

10. Poll Q 2 - Mechanical seal faces gap during
normal operation is…
a.Less than 0.2 micron
b.O.2 to 2 micron
c.2-5 micron
d.More than 5 micron

11. Seal Selection
• Fluid Characteristics
• Operating pressure
• Operating temperature
• Acceptable leakage rate (Environment norms)
• Back up arrangement
• Utility requirement
• Cost

12. BalancedVs Unbalanced
Source : Eagleburgmann

13. PusherVs Non-Pusher
• Pusher Seal – Face closing force
applied by Dynamic secondary seal,
mostly O ring, and spring
• Non-pusher (Bellow) – Face closing
force by bellow assembly.
For high temperature > 176 C
application or vapor of process fluid
tends to solidify and crystalize at
atmospheric condition
Source : Flowserve

14. Seal arrangement
• Single – For simple application
where containment or back-up
arrangement is not required
• Duel –Tandem – Safety back up
and emission control For light HC,
hazardous or toxic service
• Duel – Back-to-back – Zero
emission, Isolate process, light HC,
dirty, abrasive, vacuum service
• Duel – Face to Face - Zero
emission, Isolate process, light HC,
dirty, abrasive, vacuum service

15. Material Selection : Primary and secondary sealing
PV Limit for face material Secondary Seal – Operating temperature

16. Seal Cavity
Pressure

17. Poll Q 3 –Which is the preferred seal face
material combination as per API 682 ?
a.CarbonVs Ceramic
b.CarbonVsTC
c.CarbonVs SiC
d.Such preference is not there in API 682

18. Mechanical Seal API Plan
• For Primary Seal – 03, 11, 12, 13, 21, 23, 31, 32, 41
• Between the seal – 52, 53A/B/C, 54
• Quenching / leak detection – 62, 65, 66
• Gas seal plan – 72, 75, 76

19. Poll Q4 –Which API seal plan is the best
suitable for boiler feed pump ?
a.Plan 11
b.Plan 21
c.Plan 23
d.Plan 31

20. Installation Check Point
Material / Application Recommended flatness Remarks
Carbon, Glass filled
Teflon
2-3 light band relax after lapping. Although lapped to less than one
light band, readings be high as three light band. These
faces return to flat once they are placed against a hard-
flat face.
Tungsten carbide 1-2 light band
Silicon Carbide 1-2 light band
Ceramic 1-2 light band
High pressure > 40 bar Within 1 light band
Cryogenic Should be lapped at cryogenic temperature

21. ThankYou