Answer / mohamed

NPSH Available should be more than The Rquired NPSH.
I mean that the pressure at the suction eye of the impeller
should be more than the saturated pressure for the pumped
liquid otherwise the pumped liquid will start to evaporate
and cavitation problems will start.
i will mension here some reasons for cavitation:
- pump selection is not correct
-suction tank is not in a proper elevation.
- isolation valves are partially closed
- mesh size of pump strainer is not correct
- pump strainer is partially blocked
- the system is not vented in aproper way .
- tempertaure of pumoed liquid is deviated form normal
values.
still many reasons are there , but finally you should keep
the pressure at pump suction more than saturated pressur.

Answer / mazher

For avoiding cavitation NPSH(Available) should be always
greater than NPSH(Required).

Answer / rajesh

Cavitation takes place when liquid pressure falls below its
Vapour Pressure forming bubbles of liquid.
To avoid cavitation (NPSH)available > (NPSH)required.
We know that...
NPSH is Net Positive Suction Head.
Therefore,
NPSH = (H)atm - (H)vapour - (H) manometric
the above equation must come Positive value to avoid
cavitation!!!

how the ratchet in an micrometer works?

2 Answers  

---

can anybody provide me the HPCL apptitude papers?am having the test on this feb 19th 2008 so plz

3 Answers   HPCL,

---

1. What are good characteristics of good combustion in a boiler? 2. What do you analyze from boiler water analysis? 3. What do you treat in high alkalinity of boiler water? 4. What is a feed water pump? Dearator feed heater? 5. What is the purpose of the nozzle of impulse turbine? 6. What are the things needed to have an efficient boiler burning? 7. Name Of Parts And Each Purpose 8. What are the causes of emergency stop in a steam engine? 9. What is the normal vacuum pressure in a steam turbine atmospheric condenser? What would cause the press to falls? 10. Steam turbine (function an parts) 11. What is the boiling point of water? 12. What are the safety devices of boiler? 13. What is the effect of high alkaline water to a boiler? 14. Steps In starting boilers. 15. Small gear found in the steam turbine. 16. What is an Economizer? 17. What are the methods of heat transfer? 18. Types of pressure 19. What are the different parts of impulse reaction turbine? 20. What is the color of the flame of the boiler running in good condition? 21. What type of pump is commonly used is feed water system in auxiliary boiler? 22. What is the specific heat of water? 23. What do you do to prevent flare black? 24. What is a brake horsepower? 25. What is the purpose of a de-superheater? 26. What is the purpose of corrugated furnaces? 27. What are the causes of steam turbine failure? 28. What is the purpose of superheater? 29. Given a cutaway isometric view of the steam turbine. Examinee was asked to identify the following Parts: 30. What is thrust bearing? 31. Give five boiler mounting valves. 32. In steam boiler, what are the various test in water boiler? 33. How much calorific value of heat is needed to heat 00c of 34. What will happen if boiler backfires? 35. What is the color of flame if the boiler is running in good condition? How about when it is not in good condition? 36. How does the steam work in a steam turbine? 37. What are the causes of boiler backfire and steps in how to prevent it from happening? 38. What are the causes of high alkalinity in boiler water? 39. What are sensible heat, latent heat, and specific heat of water? 40. What are the causes of turbine vibration 41. Identify the parts of steam turbine 42. What is the normal Ph value of boiler water 43. Causes of dilution of lubricating oil in a steam turbine? 44. Explain briefly- good combustion of auxiliary boiler? 45. Method of testing or checking boiler water? 46. What is mean carry over of Aux. Boiler? 47. What are steam turbine parts usually come into damage? 48. Why must we pay attention when we drain steam in steam turbine. What factors are observed? 49. What type of pump use in boiler F.O. system? 50. What parameters to be reported when we send lubricating oil for shore analysis? 51. In boiler, what does steam and smoke goes out to the funnel. What reason? 52. Where can you find the feed check valve and feed stop valve and give the purpose of it? 53. What are the causes of troubles in boiler during operations? 54. Give the purpose of nozzle in impulse turbine? 55. What s gland sealing steam? 56. How to prevent back fire of boiler? 57. What is the used of economizer in boiler? 58. What is the seal packing gland for turbine? 59. What is the flow of steam in an impulse turbine? 60. What will happen if you blow the soot in the boiler? 61. State the purpose of air heater? 62. How to operate soot blower boiler and economizer? 63. What do you mean by A.CC.? 64. What is the thermal efficiency of a diesel engine? 65. What is a blow down valves?

0 Answers   Bhel,

---

In d thermal power plant why D/A placed on height.

4 Answers  

---

Types & function of Boiler ?

3 Answers   Bhel,

---

---

how do you come to know air is fully saturated

6 Answers   NTPC, SSB,

---

what is combined cycle & where it is used

2 Answers   NPTI, Reliance,

---

How to calculate compression spring force ?

4 Answers   L&T,

---

why constant pressure is consider for thermal diffusivity??

0 Answers  

---

what is mean by TMT STEEL

1 Answers   TATA,

---

What is meant by direct heat exchanger [or] open heat exchanger?

0 Answers  

---

I am presently working as marine engineer on ship & I wish to settle on land. So can you please suggest any short term course with 100% job guarantee?

0 Answers  

---