Hydraulic Machines Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. Which among the following principles is applicable in hydraulic turbines?

1. Newton’s second law
2. The first law of thermodynamics
3. Bragg’s law
4. None of the above

Ans. The correct answer is a. Newton’s second law

Explanation: Hydraulic machines use the momentum principle, which is governed by Newton's second law.

Ques. Hydraulic Machines fall under the category of _____.

1. Kinetic machinery
2. Roto-dynamic machinery
3. Capacitors
4. Compressors

Ans. The correct answer is b. Roto-dynamic machinery

Explanation: Hydraulic machines are categorized as roto-dynamic machinery because they use the principle of blade rotation to change the speed of the water.

Ques. What is the function of buckets and blades used in a turbine?

1. To switch off the turbine
2. Regulate the speed of the wind
3. Change the direction of the water
4. None of the above

Ans. The correct answer is c. Change the direction of the water

Explanation: A turbine uses blades and buckets to change the direction of the water. The water's momentum is also changed by these blades and buckets. As a result of the momentum change, a force is produced to rotate the shaft of a hydraulic machine.

Ques. Which among the following types of turbine is a Francis Turbine?

1. Impulse Turbine
2. Turbo turbine
3. Screw Turbine
4. Reaction turbine

Ans. The correct answer is d. Reaction turbine

Explanation: The Francis turbine is a reaction turbine because it operates on changing fluid pressure and the response supplied by fluid flow.

Ques. If a turbine is used to run an electric power generator connected to the turbine shaft, then which energy is used by it to generate electricity?

1. Rotational Energy
2. Mechanical Energy
3. Electric Energy
4. Potential Energy

Ans. The correct answer is b. Mechanical Energy

Explanation: The majority of the energies produced in a turbine are kinetic and potential energies, which are eventually transformed into usable mechanical energy.

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Short Answers Questions [2 Marks Questions]

Ques. What are hydraulic machines?

Ans. Hydraulic machines are machines and tools that operate using fluid power. A large amount of power is transmitted through small tubes and hoses in these machines. Fluid is carried throughout the machine to motors and hydraulic cylinders, where it is pressurized and sent to end effectors using control valves and tubes.

Ques. What are hydraulic turbines?

Ans. Hydraulic turbines are machines that transform water's translational kinetic energy into a turbine's rotating kinetic energy, which is subsequently turned to electrical energy by a generator connected to the turbine. In hydropower plants, either impulse or reaction turbines are used.

Ques. What is Pascal’s law?

Ans. Pascal's law (also known as Pascal's principle or the principle of fluid-pressure transmission) is a fluid mechanics principle proposed by Blaise Pascal that states that a pressure change at any point in a confined incompressible fluid is transmitted throughout the fluid, causing the same change to occur everywhere. The law was developed in 1653 by French mathematician Blaise Pascal and published in 1663.

Ques. What are the drawbacks of hydraulic systems?

Ans. One disadvantage of hydraulic systems is that they might leak, and the fluids they contain are typically corrosive to paint and seals. Another drawback is that, as compared to machines that employ gears and shafts, any power transfer results in some losses due to fluid flow resistance during the piping process.

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Long Answers Questions [3 Marks Questions]

Ques. What are the applications of hydraulic machines?

Ans. The following are the applications of hydraulic machines

• Hydraulic Brakes: Breakers, also referred to as hydraulic brakes, are braking mechanism configurations that use suitable brake fluid to transmit pressure from the control mechanism to the brake mechanism. Hydraulic brakes on automobiles work on the same basis.
• Hydraulic Lift: A Hydraulic Lift is a lift that operates by fluid pressure created by a suitable fluid. It is often used to elevate vehicles in service shops and garages.
• Hydraulic Jacks: Hydraulic jacks are more powerful than other tools because they can lift more weight.

Ques. Water is filled in a flask up to a height of 40 cm, the bottom of the flask is square with a side of 10 cm. If the atmospheric pressure is 1.01 x 105 Nm-2. Find the force exerted by the water on the bottom.

Ans. Given

• Height up to which water is filled in the flask, h = 40 cm = 0.4 m
• The side of the flask squared bottom, a = 10 cm = 0.1 m
• Pressure at the top of the flask (P₀) = atmospheric pressure

We have

Pressure at the bottom (P_b) = Pressure at top (P₀) + ⍴gh

Where

• ⍴ is the density of water
• g is the acceleration due to gravity

On substituting the values, we get

P_b = 1.01 x 10⁵ + (10³ x 9.8 x 0.4) = 1.05 x 10⁵ Nm^-2

The force exerted by the water on the bottom is

F = Pressure at the bottom x Area of the bottom surface

⇒ F = P_b x a²

⇒ F = 1.05 x 10⁵ x 0.1² = 1050 N

Ques. What are the advantages of a hydraulic system?

Ans. The advantages of a hydraulic system are

• Hydraulic systems are simple to use and precise. By employing simple levers and push buttons, a system operator may quickly start, halt, accelerate, and slow down the system.
• Because hydraulic systems have fewer moving components, they are simpler and easier to maintain.
• Only hydraulic systems can maintain constant torque or force despite variations in speed.
• Leaks in a hydraulic system are easily detected.

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Very Long Answers Questions [5 Marks Questions]

Ques. Two pistons of a hydraulic machine have diameters of 30 cm and 2.5 cm. What is the force exerted on the larger piston when 40 kg wt is placed on the smaller piston? If the smaller piston moves in through 6 cm, how much does the other piston out?

Ans. Given

• The diameter of the smaller piston, d₁ = 2.5 cm
• The diameter of the larger piston, d₂ = 30 cm
• Force exerted on the small piston, F₁ = 40 kg wt = 40 x 9.8 N

Radius of the smaller piston, r₁ = d₁/2 = 2.5/2 = 1.25 cm

Therefore, the area of the smaller piston, a₁ = πr²₁ = π(1.25)²

The radius of the larger piston, r₂ = d₂/2 = 30/2 = 15 cm

Therefore, the area of the larger piston, a₂ = πr²₂ = π(15)²

The force exerted on the larger piston is given by

F₂ = Mechanical advantage x F₁

⇒ F₂ = a₂/a₁ x F₁

⇒ F₂ = π(15)²/π(1.25)² x 40 x 9.8

⇒ F₂ = 56448 N

Now liquids are incompressible, therefore the volume of liquid moved by the smaller piston is equal to the volume of liquid moved by the larger piston i.e.

a₁X₁ = a₂X₂

Where x₁ and x₂ are the distances through which the liquid moves in smaller and larger pistons respectively.

X₂ = a₁/a₂ x X₁

⇒ X₂ = π(1.25)²/π(15)² x 6

⇒ X₂ = 0.042 cm

Hence if the smaller piston moves in through 6 cm, the larger piston moves out through 0.042 cm.

Ques. A force of 50 kgf is applied to the smaller piston of a hydraulic machine. Neglecting friction, then find the force exerted on the large piston, the diameters of the piston being 5 cm and 25 cm respectively.

Ans.Given

• The diameter of the smaller piston, d₁ = 5 cm
• The diameter of the larger piston, d₂ = 25 cm
• Force exerted on the small piston, F₁ = 50 kilogram-force = 50 x 9.8 N

Radius of the smaller piston, r₁ = d₁/2 = 5/2 = 2.5 cm

Therefore, the area of the smaller piston, a₁ = πr²₁ = π(2.5)²

The radius of the larger piston, r₂ = d₂/2 = 25/2 = 12.5 cm

Therefore, the area of the larger piston, a₂ = πr²₂ = π(12.5)²

The force exerted on the larger piston is given by

F₂ = Mechanical advantage x F₁

⇒ F₂ = a₂/a₁ x F₁

⇒ F₂ = π(12.5)²/π(2.5)² x 50 x 9.8

⇒ F₂ = 12250 N

Hence the force exerted on the larger piston is 12250 N.

Ques. What are the uses of hydraulic machines?

Ans. The following are the uses of hydraulic machines

• Cranes in construction, tractors in agriculture, forklifts in industry, and brakes in transportation are a few examples.
• Hydraulic machines utilize hydraulic fluid pressure to power movement or as a fundamental energy source.
• Hydraulic machinery includes dump trucks, aluminum or plastic extruders, cranes, jackhammers, and hose crimpers.
• Hydraulic machinery also does metal stamping, injection molding, and hose crimping.
• In amusement parks, spinning motors such as the Ferris wheel provide hours of entertainment. They use hydraulic technology to power rides and then provide motion to them.
• Hydraulics is a concept that is employed in practically every vehicle on the road. Brake fluid is an important part of a vehicle's braking system. The act of pushing the brake pedal causes a rod and piston within the master cylinder to move, resulting in the intended effect of slowing or stopping the automobile.

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