QuestionQuestion

1. List 4 important parameters that are determined by the Pv value in a seal.
2. The contact property of the interface is influenced by which component in a seal unit? What is the need for seal balance?
3. Given the following data, calculate the face area, spring pressure and balance ratios (external and internal) of a seal, for both externally acting and internally acting pressures. Is this Balanced or Unbalanced and why?
Seal face contact outer diameter, D = 61.8 mm
Effective seal balance diameter, B = 52.6 mm
Deal face contact inner diameter, d = 49.2 mm
Spring force at working length, F =188 N
4. Name the primary sealing elements in a single mechanical seal.
5. While it’s accepted that solid alumina ceramic seal rings will be considerably more expensive than ceramic coated steel rings, why should they be the preferred choice between the two types of seal ring?
6. Which dynamic secondary sealing element is the preferred type to handle axial movement? Give reasons for your answer. What type of damage does a wedge type secondary seal do to pump shafts/sleeves? Explain how this mechanism works.
7. What is the distinct advantage offered by a bellows seal? How can the design be improved to accommodate higher pressures? Which bellows material offers the best corrosion resistance?
8. Which type of single seal would you not recommend for liquids containing abrasives. Explain your reasons for not using the seal.
9. Do a comparative analysis of inboard and outboard mounting of seals.
10. Ignoring temperature limitations, what type of elastomeric material would you suggest for the following applications?
Sealing for Vacuum systems
2. Applications involving acids
3. Rotary shaft seals
4. Applications that require high tear and abrasion resistance

11. Why is it difficult to achieve a perfectly uniform load distribution across the shaft circumference, when using a single coil spring? What does this condition further lead to? What are the main advantages associated with the use of multi-coil springs?
12. Outline the nature of seal malfunction that may be caused by the following:
Incorrect pressure differential between inside and outside seal face sets
Cavitation or vaporization of liquid between sealing faces
Thermal distress of material
Large bearing clearances
13. The leakage rate in a seal while running is found to be constant. Can the reason be attributed to a damaged seal face?
State three important causes for each of the below:
Intermittent leakage
Constant dripping in a seal.

14. Which of the following conditions satisfy the requirements for sealing high speed applications?
Explain in brief:
Lower spring load at seal faces
Increased hydraulic balance ratio
Face combinations such as carbon vs. tungsten carbide
Stationary seal designs

Select from the following:
15. Rotating seal heads are normally preferred for:
A - Large sized seals
B - Smaller seals
C - For speeds above 5000 fpm
D - For speeds below 5000 fpm
16. In the double concentric type seal
A - The two seals are located side-by-side
B - The two seals are located one inside the other, but do not share a common stationary face
C - The two seals are located one inside the other, sharing a common stationary face
17. The Pv factor which is the algebraic product of the face contact pressure and the rubbing velocity is used to characterize
A - Seal leakage rate
B - Ability of a material to resist wear
C - Seal efficiency

18. A balance ratio corresponding to a value of 0.70 implies
A - Existence of a balance value of 30% of the total unbalanced condition of the present design
B - Existence of a balance value of 30% of the total balanced condition of the present design
C - Existence of a balance value of 70% of the total unbalanced condition of the present design
19. In a dynamic seal, the relationship between the seal and the housing is
A - Static
B - Dynamic
C - Neither static nor dynamic

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1. PV value of the seal is important in the sense it provides information of the suitability of mechanical seal for a particular application, PV value indicates the possible extent of wear of the seal, PV values are useful in identifying the maximum static and dynamic sealing pressures as well as the working pressures of the mechanical seals, PV limits indicates the tolerance of the various seal face materials to the varying degrees of the solid contact...
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