Lesson 5.8: Hydraulic Machines (Turbines & Pumps)

Hydraulic Machines convert fluid energy into mechanical energy (turbines) or mechanical energy into fluid energy (pumps). GATE and PSU exams often test types, working principles, performance parameters, and efficiency calculations.

🔹 1. Introduction

• Definition:

  • Turbines: Convert fluid energy into shaft work

  • Pumps: Convert mechanical work into fluid energy

• Applications: Power plants, irrigation systems, water supply networks

• Key Concepts:

  1. Head: Total energy per unit weight of fluid

  2. Efficiency: Ratio of output to input energy

  3. Specific speed: Determines type of turbine or pump

🔹 2. Turbines

• Types:

  1. Impulse Turbine: Energy converted by jet striking blades (e.g., Pelton wheel)

  2. Reaction Turbine: Energy converted by pressure drop over moving blades (e.g., Francis, Kaplan)

• Key Parameters:

  • Head (H): Height of fluid column

  • Flow rate (Q): Volume per second

  • Power (P): $P=\rho gQH\eta$

  • Efficiency ($\eta$)

• Example: Pelton wheel, H = 100 m, Q = 2 m³/s, η = 90% → Power?

$$P=\rho gQH\eta =1000\ast 9.81\ast 2\ast 100\ast 0.9\approx 1.77MW$$

🔹 3. Pumps

• Types:

  1. Centrifugal Pump: Rotating impeller imparts velocity → converts to pressure

  2. Reciprocating Pump: Positive displacement using piston or plunger

  3. Gear Pump / Screw Pump: Positive displacement for viscous fluids

• Key Parameters:

  • Head (H): Energy per unit weight delivered

  • Flow rate (Q)

  • Efficiency ($\eta$)

  • Pump Power: P=ρgQHηP = \frac{\rho g Q H}{\eta}P=ηρgQH​

• Example: Centrifugal pump, Q = 0.05 m³/s, H = 15 m, η = 70% → Power?

P=1000∗9.81∗0.05∗150.7≈10.5kWP = \frac{1000*9.81*0.05*15}{0.7} ≈ 10.5 kWP=0.71000∗9.81∗0.05∗15​≈10.5kW

🔹 4. Performance Curves

• Turbine Curves: Head vs flow rate, efficiency vs flow rate

• Pump Curves: Head vs flow rate, power vs flow rate

• Specific Speed (Ns):

Ns=NP/H5/4(Turbine)Ns = N \sqrt{P} / H^{5/4} \quad (\text{Turbine})Ns=NP​/H5/4(Turbine)

• Example: Select turbine type for given head and flow rate using Ns

🔹 5. Solved Examples (PYQ Style)

Example 1 (GATE ME 2017):
Calculate shaft power of Pelton turbine: Q = 3 m³/s, H = 80 m, η = 85%

Example 2 (PSU Exam):
Determine pump power for centrifugal pump: Q = 0.04 m³/s, H = 20 m, η = 75%

Example 3:
Select suitable turbine type (Pelton, Francis, Kaplan) for given head and flow conditions

🔹 6. Practice Exercises

1. Calculate turbine/pump power for given head, flow, and efficiency.

2. Draw and interpret performance curves of turbine/pump.

3. Determine specific speed for given turbine/pump and select appropriate type.

4. Compare centrifugal vs reciprocating pumps for given application.

5. Solve efficiency improvement problems using velocity triangles for turbines.

🔹 7. Summary

• Turbines: Convert fluid energy → mechanical work (Impulse & Reaction)

• Pumps: Convert mechanical energy → fluid energy (Centrifugal, Reciprocating)

• Key Parameters: Head, flow rate, power, efficiency, specific speed

• Applications: Power generation, irrigation, water supply, industrial systems