Hydraulic Machines Important Questions for R20 JNTU Students
Hydraulic Machines play a key role in mechanical engineering, converting fluid energy into mechanical power and vice versa. This subject is essential for R20 JNTU B.Tech Mechanical Engineering students to understand turbines, pumps, and hydraulic systems used in power plants, industries, and fluid control systems.
This blog provides chapter-wise important theory questions, numerical focus areas, practice problems, and revision tips — all tailored for Hydraulic Machines under the R20 JNTU syllabus.
Unit 1: Introduction to Hydraulic Machines
Key Theory Questions
- Define Hydraulic Machines and explain their classification.
- What is Pascal’s Law? How is it applied in hydraulic systems?
- Describe the construction and working of a hydraulic press.
- Differentiate between hydraulic lift and hydraulic crane.
- What are the advantages of using hydraulic machines over mechanical systems?
- Explain the concept of energy conversion in a hydraulic machine.
- Discuss the importance of hydraulic fluids and their properties (viscosity, compressibility, temperature stability).
- What is the function of a hydraulic accumulator?
- Explain how pressure is transmitted through liquids in a closed system.
- What are the major losses in hydraulic systems and how can they be reduced?
Numerical Focus Areas
- Pressure and force relation:P = F / A.
- Force amplification using hydraulic cylinders: F₂ = (A₂ / A₁) × F₁.
- Work and energy transfer in hydraulic systems.
- Volume displacement and fluid continuity equations.
- Efficiency of hydraulic transmission.
Unit 2: Impact of Jets and Turbines in Hydraulic Machines
Key Theory Questions
What is an impulse turbine? Explain with examples.
What is a reaction turbine? How does it differ from impulse type?
Explain Pelton wheel turbine — construction, working, and velocity triangles.
What is specific speed (Nₛ) of a turbine? Explain its importance.
Define and explain draft tube and its function.
Discuss cavitation — causes, effects, and prevention in turbines.
Compare Francis and Kaplan turbines in terms of efficiency and head.
Explain the term governing of turbines. Why is it required?
What is a hydraulic efficiency of a turbine?
Differentiate between gross head, net head, and effective head.
Numerical Focus Areas
Power developed (P) = ρ × g × Q × H × η.
Specific speed (Nₛ) = N × √P / H^(5/4).
Head loss calculation using Bernoulli’s principle.
Jet velocity and deflection angle problems.
Efficiency curves and characteristic graph interpretation.
Unit 3: Pumps in Hydraulic Machines
Key Theory Questions
- Define centrifugal pump and explain its working principle.
- What is priming and why is it necessary for centrifugal pumps?
- Define manometric head and its components.
- Discuss the classification of pumps based on working principle and flow direction.
- What is NPSH (Net Positive Suction Head) and why is it important?
- Explain the specific speed of a pump and its significance.
- What are the differences between reciprocating and rotodynamic pumps?
- Explain the construction and working of a reciprocating pump.
- Define multistage pumps and explain their purpose.
- What are losses in centrifugal pumps and how can they be minimized?
Numerical Focus Areas
Efficiency (η) = Output Power / Input Power.
Calculation of discharge (Q), head (H), and power (P).
Affinity laws for pump similarity:
Q ∝ N
H ∝ N²
P ∝ N³
NPSH available vs NPSH required.
Calculation of slip, coefficient of discharge, and volumetric efficiency.
Unit 4: Performance Testing and Characteristics of Hydraulic Machines
Key Theory Questions
Explain the purpose of performance testing in hydraulic machines.
What are characteristic curves of a pump and turbine?
Discuss the head-discharge and efficiency curves for pumps.
Explain unit quantities: unit speed, unit discharge, and unit power.
What are the similarity laws in model testing of hydraulic turbines?
Discuss the efficiency of a turbine at part and full load.
What is thoma cavitation factor and how is it determined?
Explain the term specific energy in context of turbine operation.
How are hydraulic coefficients used to analyze performance?
Differentiate between model testing and prototype testing.
Numerical Focus Areas
- Use of characteristic equations to find head and flow at different speeds.
- Determination of best efficiency point (BEP).
- Performance under varying heads.
- Calculation of unit parameters for scaling models.
- Head losses due to friction and fittings in suction/delivery pipes.
Unit 5: Hydraulic Systems and Applications
Key Theory Questions
- Explain working of hydraulic brakes and hydraulic steering.
- What is a hydraulic accumulator and its applications?
- Describe hydraulic intensifier — working and advantages.
- Discuss fluid coupling and torque converter operation.
- Explain hydraulic lift system with neat sketch.
- Compare hydraulic and pneumatic systems.
- What are servo mechanisms in hydraulic control?
- Explain flow control valves and pressure relief valves.
- What are filters and strainers, and why are they essential?
- Discuss the role of hydraulic fluids and the importance of maintenance.
Numerical Focus Areas
- Power transmission through hydraulic circuits.
- Flow rate and actuator speed calculations.
- Pressure loss in pipelines and valves.
- Design of hydraulic jack and press based on load capacity.
- Energy efficiency in hydraulic drives.
Practice Questions & Problems for Hydraulic Machines
A turbine runs at 300 rpm, delivers 500 kW under a head of 50 m with an efficiency of 85%. Determine the flow rate.
A centrifugal pump has a flow of 0.08 m³/s under a head of 20 m at 1450 rpm. If speed is reduced to 1000 rpm, determine the new flow and head using affinity laws.
Determine the specific speed (Nₛ) of a pump which runs at 1460 rpm, has flow 0.12 m³/s and head 25 m.
A hydraulic press has a small piston of diameter 50 mm and large piston of diameter 250 mm. If force on small piston is 500 N, determine the force on large piston (neglect friction).
For a Kaplan turbine, if the head is 15 m, flow is 30 m³/s and efficiency is 92%, calculate the power output.
A pump test is done at 2900 rpm giving H=40 m, Q=0.06 m³/s, P=10 kW. Find the head, flow, and power at 1450 rpm assuming similarity.
Determine NPSH (available) for a pump operating at inlet pressure of 150 kPa, vapor pressure of liquid 0.02 MPa, fluid density 1000 kg/m³, suction head 2 m, velocity head negligible.
A reaction turbine has specific speed Nₛ=1200, head is 10 m and flow 20 m³/s. Determine the rotational speed if power is 950 kW.
The efficiency of a pump is 78% at design operating point. The brake power input is 12 kW. Calculate the delivered fluid power.
A hydraulic machine has piston area ratio of 4:1. If the smaller piston moves 0.1 m, how far does the larger piston move? Also determine force amplification if F_small = 400 N
Tips & Revision Strategy for Hydraulic Machines
- Memorise all important formulas for hydraulic machines — power, head, specific speed, affinity laws.
- Always label diagrams clearly: turbine runner, pump impeller, suction pipe, draft tube etc.
- Practice derivations for performance and selection of hydraulic machines (specific speed, NPSH, affinity laws).
- Solve previous year R20 JNTU papers focusing on hydraulic machines topics.
- Use units consistently (m, m³/s, kW, rpm) and note conversions — avoid mistakes due to unit mismatch.
- For numerical problems, always state assumptions (neglect losses, frictionless shaft, etc).
- Understand real‐world applications of hydraulic machines to relate theory and improve understanding (e.g., in dam turbines, pump stations).
Conclusion
Mastering the subject of Hydraulic Machines is not just about formula memorisation but understanding the energy conversion, fluid‐mechanics principles, machine performance, and selection criteria. If you focus on the chapter‐wise key theory, practice the numerical focus areas, and reinforce your understanding through the problems given above, you’ll be well prepared for your R20 JNTU exams and real‐life design applications.
Stay consistent in practice, use the diagrams and formulas intelligently, and connect the questions to real hydraulic systems. Good luck building your hydraulic machines expertise with Mechworlz!
