Skip to main content

Part -5 Most commonly asked Mechanical Interview Questions



Most commonly asked Mechanical Interview Questions with answer


1. Why the Centrifugal Pump is called High Discharge pump?
Ans. Centrifugal pump is a kinetic device. The centrifugal pump uses the centrifugal force to push out the fluid. So the liquid entering the pump receives kinetic energy from the rotating impeller. The centrifugal action of the impeller accelerates the liquid to a high velocity, transferring mechanical (rotational) energy to the liquid. So it discharges the liquid in high rate. It is given in the following formulae:
Centrifugal force F= (M*V2)/R.
Where,
M-Mass
V-Velocity
R-Radius

2. How Cavitation can be eliminated by Pump?Ans. Cavitation means bubbles are forming in the liquid.
  • To avoid Cavitation, we have to increase the Pump size to One or Two Inch
  • To increase the pressure of the Suction Head
  •  Decrease the Pump Speed.
3. Why Cavitation will occur in Centrifugal Pump and not in Displacement Pump?Ans. The formation of cavities (or bubbles) is induced by flow separation, or non-uniform flow velocities, inside a pump casing. In centrifugal pumps the eye of the pump impeller is smaller than the flow area of pipe. This decrease in flow area of pump results in increase in flow rate. So pressure drop happened between pump suction and the vanes of the impeller. Here air bubbles or cavities are formed because of liquid vapour due to increase in temperature in impeller. This air bubbles are transmitted to pump which forms cavitation.

4. Which Pump is more Efficient Centrifugal Pump or Reciprocating Pump?Ans. Centrifugal pump. Because flow rate is higher compared to reciprocating pump. Flow is smooth and it requires less space to install. Lower initial cost and lower maintenance cost.

5. Why Centrifugal Pump is not called as a Positive Displacement Type of Pump?Ans. The centrifugal has varying flow depending on pressure or head, whereas the Positive Displacement pump has more or less constant flow regardless of pressure.
Likewise viscosity is constant for positive displacement pump where centrifugal pump have up and down value because the higher viscosity liquids fill the clearances of the pump causing a higher volumetric efficiency. When there is a viscosity change in supply there is also greater loss in the system. This means change in pump flow affected by the pressure change.
One more example is, positive displacement pump has more or less constant efficiency, where centrifugal pump has varying efficiency rate.

See related more FAQs <<<< Click Here >>>>


Labels:

Popular posts from this blog

Part -2 Most commonly asked Mechanical Interview Questions

Most commonly asked Mechanical Interview Questions 1. What is the difference between Critical Speed and Whirling Speed? Ans. In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration. The resulting resonance occurs regardless of orientation.Whirling Speed is due to the unbalanced forces acting on a rotating shaft. 2. How a Diesel Engine Works as Generator? Ans. Diesel engine is a prime mover, for a generator, pump,and for vehicles etc. generator is connected to engine by shaft. mostly in thermal power plat ,there is an engine is used to drive generator to generate power. 3. Explain Second Law of Thermodynamics? Ans. The entropy of the universe increases over tim...
Read more

LIQUID (DYE) PENETRATION TEST (D.P.T.)

LIQUID (DYE) PENETRATION TEST INTRODUCTION A liquid penetrant test is non-destructive type of testing to detect flaws that are open to the surface. e.g. cracks, seams, laps, lack of bond, porosity, cold shuts etc. can be effectively used not only in the inspection of ferrous metals but is especially useful for non-ferrous metal products and on non-porous, non-metallic materials such as ceramics, plastics and glass. PRINCIPLE OF OPERATION The principle of liquid penetrant test is that the liquids used enter small openings such as cracks or porosities by capillary action. They are influenced by factors such as the condition of the surface of material and the interior of the discontinuity. For liquid to penetrate effectively, the surface of the material must be thoroughly cleaned of all material that would obstruct the entrance of the liquid into the defect. After cleaning, the liquid penetrant is applied evenly over the surface and allowed to remain long enough to permit penetration i...
Read more

VISUAL INSPECTION OF WELDING

VISUAL  INSPECTION OF WELDING INTRODUCTION Inspection starts with examination of the material prior to fabrication, scabs, seams, scale or other harmful surface conditions may be detected in visual inspection. The inspector should check the following : Weld preparation, dimensions and finish.  Clearance dimensions of backing strips.  Alignment and fit up to the pieces being welded.  Verification of cleanliness.  Visual Inspection During Welding Visual inspection checks details of the work while welding is in progress. Among the details to be checked are : Welding process.  Cleaning.  Preheat and inter pass temperature.  Joint preparation.  Filler metal.  Flux or shielding gas.  Chipping, grinding, or gouging.  Post heating temperature and time.  Visual Inspection After Welding Visual inspection is useful for finished-product verification of such items as : Profile irregularities of the weldment....
Read more