# Hydraulic Machines Questions and Answers – Efficiency of Pelton Turbines

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This set of Hydraulic Machines Multiple Choice Questions & Answers (MCQs) focuses on “Efficiency of Pelton Turbines”.

1. The hydraulic efficiency of Pelton turbine will be maximum when blade velocity is equal to _______
a) V/2
b) V/3
c) V/4
d) V/5

Explanation: Hydraulic efficiency is defined as ratio between power given by water to runner of turbine and to the power supplied by water at inlet of the turbine. This efficiency will be maximum when differentiating it with “u” and it is obtained as u=v/2.

2. In Pelton turbine ___________ is defined as ratio between power delivered to runner and power supplied at inlet of turbine.
a) Mechanical efficiency
b) Volumetric efficiency
c) Hydraulic efficiency
d) Overall efficiency

Explanation: Hydraulic efficiency is defined as ratio between power given by water to runner of turbine and to the power supplied by water at inlet of the turbine.

3. The maximum efficiency of Pelton turbine is _________
a) 80%
b) 70%
c) 50%
d) 88%

Explanation: We know that efficiency will be Maximumwhen blade velocity is equal to half of its jet velocity upon substitution we get efficiency as 50%.

4. In Pelton turbine product of mechanical efficiency and hydraulic efficiency is known as _____________
a) Mechanical efficiency
b) Volumetric efficiency
c) Hydraulic efficiency
d) Overall efficiency

Explanation: Overall efficiency is defined as ratio of power available at shaft of turbine to power supplied at the inlet of turbine which is also product of mechanical and hydraulic efficiency.

5. Among the following which turbine has least efficiency?
a) Pelton turbine
b) Kaplan turbine
c) Francis turbine
d) Propeller turbine

Explanation: Pelton is impulse turbine and remaining are reaction turbine, efficiency of reaction turbine is more compared to impulse turbine.

6. In Pelton ____________ is ratio of volume of water actually striking the runner and volume of water supplied to turbine.
a) Mechanical efficiency
b) Volumetric efficiency
c) Hydraulic efficiency
d) Overall efficiency

Explanation: Volumetric efficiency is ratio between volume of water actually striking the runner of turbine and volume of water supplied to the turbine.

7. In Pelton turbine the ratio of volume available at shaft of turbine and power supplied at the inlet of the turbine is _______
a) Mechanical efficiency
b) Volumetric efficiency
c) Hydraulic efficiency
d) Overall efficiency

Explanation: Overall efficiency is defined as ratio of power available at shaft of turbine to power supplied at the inlet of turbine which is also product of mechanical and hydraulic efficiency.

8. The expression for maximum hydraulic efficiency of Pelto turbine is given by ______________
a) (1+cos k)/2 where k is outlet blade angle
b) (2+cos k)/2 where k is outlet blade angle
c) (3+cos k)/2 where k is outlet blade angle
d) (4+cos k)/2 where k is outlet blade angle

Explanation: Hydraulic efficiency is defined as ratio between power given by water to runner of turbine and to the power supplied by water at inlet of the turbine. Its maximum value is obtained by replacing u=v/2 and it is (1+cos k)/2 where k is outlet blade angle.

9. In the expression for overall efficiency of turbine, which is p/ (k*g*q*h), where “k” is known as _______
a) Specific density of liquid
b) Density of liquid
c) Specific gravity of liquid
d) Volume of liquid

Explanation: Overall efficiency is defined as ratio of power available at shaft of turbine to power supplied at the inlet of turbine which is also product of mechanical and hydraulic efficiency. Its expression is given by p/ (k*g*q*h) where k is density of liquid.

10. In Pelton turbine hydraulic efficiency is product of mechanical efficiency and overall efficiency.
a) True
b) False

Explanation: The above statement is false generally overall efficiency is product of mechanical and hydraulic efficiency.

11. The expression for hydraulic efficiency is given by
a) 2(V1-u)[1+cos k]u/V1*V1
b) 2(V1+u)[1+cos k]u/V1*V1
c) 2(V1-u)[1-cos k]u/V1*V1
d) 2(V1+u)[1+cos k]u/V1*V1

Explanation: Hydraulic efficiency is ratio of power delivered to runner to power supplied at inlet of turbine upon substituting the mathematical terms we get expression as follows.
Where, V1=inlet jet velocity, u=blade velocity, k=outlet blade angle

12. In Pelton turbine inlet velocity of jet is 85.83m/s, inlet and outlet whirl velocities be 85.83 and 0.143 and blade velocity be 38.62 then its hydraulic efficiency is ___________
a) 90.14%
b) 80%
c) 70%
d) 85%

Explanation: Substitute the above given values in expression for hydraulic efficiency which is given by expression 2[Vw1+Vw2] u/V1*V1 and we get it as 90.14%.

Sanfoundry Global Education & Learning Series – Hydraulic Machines.

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