Few Questions Related to Pump / Alignment / Pump Piping

1. What are different types of pumps? 
Answers :- Basically there are two types of pumps.
A. Centrifugal pump.
B. Positive displacement pump.

2. What are the different types of centrifugal pump?
Answers :- 
Different types of centrifugal pump are:
A. Single stage or
B. Multi-stage

3. What are the centrifugal pumps?
Answers :- Centrifugal pumps are the mechanical devices which pump or transport various fluids by converting their rotational kinetic energy into hydrodynamic energy.

4. What are the reasons for over load of pump?
Answers :- 
  • More flow
  • High speed
  • Reverse rotation of pump
  • Pump discharge kept open to atmosphere
  • Internal friction in impeller & wear ring or impeller & casing
  • More tightened gland packing
  • No lubricant in bearing or bearing seized
5. What are the potential reasons for pump vibrations?
Answers :-  
  • Overloading of pump
  • Reverse rotation of pump
  • Impeller rubbing inside the casing
  • Misalignment
  • Damaged bearing
  • Shaft run out
  • Shaft imbalance.
6. Too much noise coming from pump inside, what does this mean?
Answers :-  
  • Air lock in pump
  • Overloading of pump
  • Pump discharge line is less than actual required
  • Cavitation
  • No lubricant in bearings
7. What are the common mistakes done during pump installation?
Answers :-  
  • Choosing poor foundation
  • Note: Pump foundation weight should be 3 to 4 times the pump weight
  • Lesser size suction pipe line
  • Lesser size discharge pipe line
  • Interchanging concentric & eccentric reducers
8. What is the basic difference between single stage and multi-stage centrifugal pump?
Answers :- 
The Single stage pump has one impeller and multi-stage pump has two or more impellers in series. The discharge of one impeller is the suction of the next one and the head developed in all the stages are totaled.

9. Where the centrifugal pumps find applications in power plants?
Answers :-  
  • Boiler feed water pump
  • Auxiliary & main cooling water pumps
  • Raw water transfer pumps
  • Condensate extraction pump,
  • Deaerator & feed water tank make up pumps
  • Firefighting water pumps
  • UF & RO feed water pumps
  • MGF feed pump
  • Degassed water transfer pumps
  • Sometimes lube & control oil pumps.
10. How many types of centrifugal pump are available based on the suction and discharge arrangement?
Answers :-  Based on the suction and discharge arrangement, the type of centrifugal pumps available is: 
  • End suction top discharge.
  • Top suction top discharge.
  • Side suction side discharge.

11. What are the different types of casing?
Answers :-  Casings are generally of two types: Volute and Circular. The impellers are fitted inside the casings.

12. Define the working mechanism of centrifugal pump?
Answers :-  A centrifugal pump is one the simplest pieces of equipment in any process plant. Its purpose is to convert energy of prime mover (an electric motor or turbine) first into velocity or kinetic energy and then into pressure energy of a fluid that is being pumped. The energy changes occur by virtue of two main parts of the pump, the impeller and the volute or diffuser. The impeller is rotating part that converts drivers energy into the kinetic energy. The volute or diffuser is the stationary part that converts the kinetic energy into pressure energy.

13. What do you mean by cavitation in pump?
Answers :-  A pump is designed to handle liquid, not vapor. The satisfactory operation of pump requires that vaporization of the liquid does not occur at any condition of operation. This is so desired because when a liquid vaporizes its volume increases very much. For example, 1 ft3 of water at room temperature becomes 1700 ft3 of vapor at the same temperature. The vaporization begins when vapor pressure of the liquid at the operating temperature equals the external system pressure, which in an open system is always equal to atmospheric pressure. Any decrease in external pressure or rise in operating temperature can induce vaporization. The vapor pressure occurs right at the impeller inlet where a sharp pressure drop occurs. The impeller rapidly builds up the pressure, which collapses vapors bubbles causing cavitation and damage the pump internals. This is avoided by maintaining sufficient NPSH. (Cavitation implies cavities or holes in the fluid we are pumping. These holes can also be described as bubbles, so cavitation is really about the formation of bubbles and their collapse. Bubbles form whenever liquid boils. It can be avoided by providing sufficient NPSH.)

14. What is a positive displacement pump and why is it called so? How does it differ from centrifugal pumps?
Answers :-  Positive displacement pumps are called so because of ''no fluid comes back to its casing or say cam ring, during pumping out. A locking is formed by meshing gears, sliding vanes, that acts like a seal and whole amount of fluid goes through delivery line. This amount is called positively displaced amount and that's why its called positive displacement pump.
Whereas in centrifugal pumps a small amount of fluid gets back into the casing due to its casing design, designed so to churn the fluid in casing even when delivery valve is fully closed without causing any damage to the pump. But if you close the valve fully in a positive displacement pump then something will break, but centrifugal pumps firstly develop the head, those are designed for, and then start churning the fluid in casing when delivery valve is closed.

15. What are the Types of Centrifugal Pump Losses ?
Answers :- Losses in a Centrifugal pump are classified into five types namely
  • Mechanical losses
  • Impeller losses
  • Leakage losses
  • Disk friction losses and 
  • Casing hydraulic losses.

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