# Hydraulic Machines Questions and Answers – Efficiency of Draft Tube

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

1. The efficiency of the draft tube depends on the ______
a) Heat
b) Pressure
c) Temperature
d) Pressure and temperature

Explanation: The efficiency of the draft tube is defined as the ratio of actual conversion of kinetic energy into the pressure energy. The pressure energy and kinetic energy is present at the inlet of the draft tube.

2. Draft tubes have _________ shafts
a) Horizontal
b) Vertical
c) Circular
d) Cross sectional

Explanation: Draft tubes have vertical shafts. The pressure energy and kinetic energy is present at the inlet of the draft tube.

3. Draft tubes are situated at the outlet in____________
a) Pelton
b) Reaction
c) Kaplan
d) Francis

Explanation: Turbine extracts energy and converts it into useful work. Turbine is a vortex related device. Draft tubes are not used in Pelton wheels. Draft tube is a tube that is installed in power turbines.

4. Efficiency of a draft tube is directly proportional to its __________
a) Temperature
b) Pressure
c) Velocity
d) Density

Explanation: The efficiency of the draft tube gives difference of the kinetic energy between the inlet and the outlet tube losses. It is directly proportional to its velocity.

5. Z is a draft tube is _______
a) Temperature difference
b) Pressure drop
c) Kinetic energy difference

Explanation: Height of tail race which is referenced as datum line is equal to zero. It is denoted as ‘Z’. It plays an important role to determine its efficiency.

6. Draft tube operates at ______
a) Same efficiency
b) Different efficiency
c) Turbine
d) Pump

Explanation: Draft Tube allows turbine to be placed above the tail race and simultaneously allows it to operate at the same efficiency if it was placed at the tail race.

7. The draft tube is an ________
a) Interior tube
b) Exterior tube
c) Tank depth alternator
d) Nozzle tube

Explanation: The simple elbow draft tube is placed close to the tail race. It consists of an extended elbow type tube. It is mainly used in the Kaplan turbine. It is placed close to the tail race of the turbine.

8. What type of pressure does the draft tube depend upon?
a) Gauge pressure
b) Atm pressure
c) Normal pressure
d) Normal and Atm pressure

Explanation: Draft tube is mainly used to determine the gauge pressure of the turbine and pumps and is located at the inlet of the turbine.

9. Gauge pressure of the draft tube is denoted by _____
a) P
b) h
c) z
d) x

Explanation: Gauge pressure of the draft tube is denoted by ‘P’. It helps to determine the pressure of the fluid in the draft tube.

10. Draft tube allows turbine to be placed below the tail race.
a) True
b) False

Explanation: The draft tube helps to cut down the cost of excavation. The draft tube is placed close to the tail race. The turbine pressure head is increased by decreasing the velocity at the draft tube. Draft tube allows turbine to be placed above the tail race.

Sanfoundry Global Education & Learning Series – Hydraulic Machines.

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