1. SEAL FACE PROPERTIES

2. FOR A SEAL TO WORK… FACE FLATNESS
SEAL FACES ARE TO BE FLAT TO ONE LIGHT BAND OF A HEILIUM ARC LAMP REFLECTED THROUGH A QUARTZ REFERENCE OPTICAL FLAT
ONE LIGHT BAND = INCHES
OR 11.6 ONE MILLIONTHS OF AN INCH

3. Optically Flat Faces
100 psi
0 psi
Rotary
Face
Stationary

4. FOR A SEAL TO WORK… FACE LUBRICATION
BOUNDARY LAYER FILM OF LIQUID FILLS PORES AND IMPERFECTIONS. IT IS PROVIDED BY THE LIQUID IN THE STUFFING BOX.
DRY RUNNING OF A PUMP SEAL FOR ONLY A FEW SECONDS MAY DESTROY IT.
UNLESS IT IS DESIGNED THAT WAY!

5. Microscopic Face Lubrication
100 psi
Rotary
Face
Stationary
Face
0 psi

6. Pressure Drop
100 psi
0 psi

7. Pressure Drop & Vaporization
100 psi
0 psi
25 psi
50 psi
Liquid
Liquid + Vapor
Vapor + Liquid
Vapor

8. Convergent Seal Faces
100 psi
0 psi
Rotary
Face
Stationary

9. Convergent Seal Faces
100 psi
0 psi
Rotary
Face
Stationary

10. Convergent Seal Faces
100 psi
0 psi
Rotary
Face
Stationary

11. Divergent Seal Faces
100 psi
0 psi
Rotary
Face
Stationary

12. Divergent Seal Faces
100 psi
0 psi
Rotary
Face
Stationary

13. Divergent Seal Faces
100 psi
Rotary
Face
Stationary
Face
0 psi

14. SEAL BALANCE

15. Balance Line
Unbalanced Seal
Face OD Line
Face ID Line

16. BALANCED VS. NON-BALANCED
When speaking of “Balance” in reference to mechanical seals, we are not talking about Mechanical or Rotational Balance. Instead, we are referring to Hydraulic Balance.
Since mechanical seals are subject to stuffing box pressure, this pressure is utilized to achieve and maintain seal face closure in a non-balanced seal.
If stuffing box pressure is very high, typically over 100psi., then the closing force may be too great to allow the “Boundary Layer Liquid” that lubricates the faces to be sufficient and the faces will wear prematurely.
A balanced seal compensates for higher pressures by locating the seal faces such that stuffing box pressure has less effect on face closure.

17. Seal Balance

18. Face OD Line Face ID Line Balance Line
A non-balanced seal has faces located
outside the “Balance Diameter” of the
seal. Stuffing box pressure is applied
to the faces virtually evenly.
Face OD Line
Face ID Line
Balance Line

19. Unbalanced Seal Face Areas
Green+Red=Pressure Area
Green+Purple=Face Contact Area
Balance Line
Face ID Line
Face OD Line

20. Face OD Line Balance Line Face ID Line
The faces of a balanced seal are located so that
a portion of the face contact occurs inside the
balance diameter resulting in reduced closing
force due to stuffing box pressure.
Face OD Line
Balance Line
Face ID Line

21. Balanced Seal Face Areas
Green+Red=Pressure Area
Red+Purple=Balanced Area
Balance Line
Face ID Line
Face OD Line

22. Face OD Line Balance Line Face ID Line
Most metal bellows seals are balanced.
Face OD Line
Balance Line
Face ID Line

23. END SEAL FACE PROPERTIES