Hydraulics and Pneumatics Experimental Questions Mechanical Engineering


1 Classify hydraulic fluids. What are the desirable properties of hydraulic fluid?

  • Hydraulic oil is a non-compressible fluid that is used to transfer power within hydraulic machinery and equipment.
  • Hydraulic fluid, consider the following characteristics: viscosity, viscosity index, oxidation stability, and wear resistance

2 Explain different types of hydraulic fluids.

  • Petroleum-based or mineral-based fluids
  • Water-based fluids
  • Synthetic fluids 

3 What is the efficiency of the vane pump?

The vane pump volumetric efficiency at 1200 rpm decreases from 97.3% at 500 psi to 84% at 2500 psi.

4 Differentiate between the hydraulic system and the Pneumatics system.

  • Hydraulic systems use liquids like water and oil to transmit power
  • Where pneumatic systems use air to transmit power. 

5 What are the energy losses in the hydraulic system?

frictional energy loss

6 Classify pumps in the hydraulic system. Define various efficiencies of the pump.

  • Pumps are classified as either positive-displacement or non-positive-displacement
  • Efficiencies—mechanical, volumetric, and hydraulic.

7 What is the performance characteristic of the gear pump?

It delivers a smooth pulse-free flow proportional to the rotational speed of its gears.

8 What is the efficiency of the piston pump?

Piston pumps have very high volumetric efficiency (over 98%) 

9 What is the difference between gear pump and vane pump?

  • A gear pump is a type of positive displacement (PD) pump
  • vane pump is a positive-displacement pump

10 What is the efficiency of the gear pump?

Volumetric efficiencies of gear pumps run as high as 91 percent

11 What are various factors are to be considered for the selection of pumps for specific applications.

  • The fluid to be pumped, its chemical characteristics, its viscosity and density, and temperature
  • The volume and head at which the volume is required
  • The availability of electric power
  • The initial and running costs
  • The nature of pumping
  • The duty cycle needed
  • Maintenance considerations

12 Explain the factors that justify the pump selection.

  • Capacity
  • Power: The power which is used for running pumps should be available easily at a low cost.
  • Maintenance
  • Efficiency
  • Depreciation
  • Cost of labor
  • The number of pumping

13 State advantages, disadvantages, and applications of the hydraulic system.

  • Advantages of hydraulic systems include power, accuracy, efficiency, and ease of maintenance.
  • Disadvantages are they can leak, which makes them messy, and the fluids inside them are often caustic to paint and some seals.
  •  Power steering, shock absorbers, windshields, and brake are the common applications of hydraulics in vehicles.

14 Explain the construction and working of the gear pump.

Gear pumps use the actions of rotating cogs or gears to transfer fluids. The rotating element develops a liquid seal with the pump casing and creates suction at the pump inlet. Fluid, drawn into the pump, is enclosed within the cavities of its rotating gears and transferred to the discharge.

To study demonstration of Hydraulic Trainer

1 Draw the regenerative circuit.

A Regenerative circuit is a system that is used to speed up the extension stroke of the double-acting single rod hydraulic cylinder.

2 What are the applications of Speed control circuits?

Speed controllers are mainly used in remote control boats and cars 

3 Draw the Sequencing circuit.

Sequencing circuits are those that automatically program two or more cylinders on a machine to cause them to extend and retract in a predetermined sequential order on every cycle.

4 Draw the Speed control circuit.

An electronic speed control (ESC) is an electronic circuit that controls and regulates the speed of an electric motor. 

5 What are the applications of the Sequencing circuit?

A typical application would be when maintained clamping pressure is required in the primary circuit while work is being performed in the secondary circuit.

6 Draw the Transverse and feed circuit.

Raoid transverse and feed circuits are mostly used where two different speeds for operations are needed. Examples like punch and press, drill, etc. here the main components are reservoir tank, feed pump, one-directional flow control valve, 2 DCV (3/2 & 4/3), and double-acting cylinder.

8 What are the applications of the Regenerative circuit?

The rod end of the cylinder is connected to the main pressure line, so the oil which normally would be discharged to a tank will join with the pump oil, increasing the speed of the piston.

9 What is a meter in the circuit?

A meter is any device built to accurately detect and display an electrical quantity in a form readable by a human being.

10 Explain the significance of the meter-out circuit? or What is the meter-out circuit?

Meter-out circuits provide accurate speed control even with reversing loads.

11 Explain the significance of meter in the circuit?

 In the analysis and testing of circuits, there are meters designed to accurately measure the basic quantities of voltage, current, and resistance.

To study demonstration of Pneumatic Trainer

1 Draw automatic reciprocating circuit.

The hydraulic circuit produces continuous reciprocation of a double-acting cylinder using two sequence valves. Each sequence valve senses the completion of stroke by the corresponding build-up pressure. Each check valve and the corresponding pilot line prevent the shifting of the four-way valve until the particular stroke of the cylinder is completed.

2 Explain the significance of the automatic reciprocating circuit

Produces continuous reciprocation of a double-acting cylinder using two sequence valves

5 What is an Electro-pneumatic circuit?

In electro-pneumatics, the pneumatic components are controlled by using electrical and electronic circuits. Electronic and electromagnetic sensors, electrical switches and industrial computers are used to replace the manual control of a pneumatic system.

6 Explain pneumatic circuit involving Shuttle valve.

A shuttle valve is a type of valve which allows fluid to flow through it from one of two sources. Generally, a shuttle valve is used in pneumatic systems, although sometimes it will be found in hydraulic systems.

7 Explain pneumatic circuit involving Quick exhaust valve.

Quick exhaust valves operate by increasing the speed of the pneumatic cylinder's rod in order to expel the exhaust air at the port of the cylinder directly. One quick exhaust valve is used in each port of the cylinder to ensure an increase in the speed of the rod in both directions.

9 What is the significance of the Quick exhaust valve?

One quick exhaust valve is used in each port of the cylinder to ensure an increase in the speed of the rod in both directions. The use of a quick exhaust valve in a pneumatic system helps to increase cycling speed, in turn, ensures a much smaller valve to be effectively used for the process.

10 What is the significance of the Shuttle valve?

Its purpose is to seal off one or the other of the inlet ports. There is a shuttle seat at each inlet port. When a shuttle valve is in the normal operating position, fluid has a free flow from the normal system inlet port, through the valve, and out through the outlet port.

11 Explain FRL Unit. Draw its symbol.

An FRL unit is comprised of a filter (F), regulator (R), and lubricator (L). They are often used as one unit to ensure clean air in a pneumatic system but can also be used individually.

Pressure Relief Valve

1 What is a pressure relief valve?

A pressure Relief Valve is a safety device designed to protect a pressurized vessel or system during an overpressure event

3 What are the applications of pressure relief valves?

Pressure relief valves are used in a wide range of specifications where pressure levels are critical for smooth operations such as oil and gas, petrochemical, and power generation using steam, air, gas or liquid.

4 What is a flow control valve?

A flow control valve regulates the flow or pressure of a fluid. Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges.

5 What are the applications of flow control valve

System operators can use a flow control valve to rapidly depressurize a serviceable hose and change fittings quickly.

6 What are the advantages of a pressure relief valve?

  • They vent the fluid to safeguard the system from overpressure.
  • They reclose and prevent loss of fluid when system pressure returns back to acceptable.
  • Installation of the PRV system minimizes damage to system components.

7 What are the types of flow control valves?

Types of valves are available such as ball, diaphragm, needle, butterfly, and plug valves. 

8 Which are the other types of valves?

  • Isolation Valves: Ball, butterfly, diaphragm, gate, pinch, piston, and plug valves.
  • Regulation Valves: Ball, butterfly, diaphragm, globe, needle, pinch, and plug valves.
  • Safety Relief Valves: Pressure release and vacuum relief valves.

9 Explain the working of the pressure relief valve.

Pressure relief valves (safety relief valves) are designed to open at a preset pressure and discharge fluid until the pressure drops to acceptable levels.

10 Explain the working of the flow control valve.

A flow control valve adjusts and controls the volume flow of air within a pneumatic system. They can often be used to adjust the speed of operation of an actuator. They should not be confused with pressure controllers or regulators.

Linear and Rotary Actuators

1 What is the difference between linear and rotary actuators?

  • Linear actuators are a type of actuator that converts the rotational motion in motors into linear or straight.
  • A rotary actuator is an actuator that produces a rotary motion or torque.

2 Explain the linear actuators.

A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor.

3 What are the types of linear actuators?

  • Mechanical or electromechanical linear actuators.
  • Hydraulic linear actuators.
  • Pneumatic linear actuators.
  • Piezoelectric actuators.

4 What are the types of rotary actuators?

The three most commonly used types are rack and pinion, vane, and helical. 

5 Explain the rotary actuators.

A rotary actuator is a pneumatic cylinder used to provide a turning or angular movement, allowing a stroke in an oscillating motion through a defined angle.

6 What are the applications of linear actuators?

Applications involve lifting, lowering, sliding, adjusting, and tilting objects. 

7 What are the functions of rotary actuators?

A rotary actuator is a pneumatic cylinder used to provide a turning or angular movement, allowing a stroke in an oscillating motion through a defined angle. 

8 What are the applications of rotary actuators?

Rotary actuators are used in many motion-control systems as well to operate, for instance, pick-and-place handlers or clamps. These are often air-powered but can be electrically or even hydraulically powered. Miniature actuators capable of very fine movement may be sourced as well.

9 What are the functions of linear actuators?

An electric linear actuator is a device that converts the rotational motion of an AC or DC motor into linear motion. 

10 Explain the construction and working of the single-acting cylinder.

The working principle of single-acting cylinders is to transfer hydraulic fluids or an output force in one direction only. Within the cylinder, the piston rod can push outwards but cannot pull back, therefore requiring a force in the opposite direction to return the rod back to its original position.

11 Explain the construction and working of the double-acting cylinder.

Double-acting cylinder: The force exerted by the compressed air moves the piston in two directions in a double-acting cylinder. They are used when the piston is required to produce thrust not only on the advanced movement but on the return. 


1 Explain the simple hydraulic system.

The simplest hydraulic system consists of a pair of cylinders with moveable pistons in each and the whole system is filled with fluid. 

2 How the best hydraulic system is designed?

The design of a hydraulic system involves the following basic steps

(1) selection and sizing of components,

(2) determining the system operating pressure and flow rate, and

(3) finding the component specifications to meet the design objectives.

3 List the different hydraulic systems used in industries.

  • Internal Gear Pumps.
  • External Gear Pumps.
  • Screw pumps.

4 What is a hydraulic power pack?

A hydraulic power pack is a stand-alone assembly consisting of a drive motor, hydraulic pump, and hydraulic fluid tank.

5 What is the difference between the hydraulic system and a pneumatic system?

Hydraulic systems

  • The working fluid is hydraulic oil.
  • As oil is incompressible, oil can be pressurized to very high pressure. (500 bar or even more)

Pneumatic systems

  • Working fluid is compressed air.
  • Air is compressible; hence air can be pressurized to lesser pressure. (Only up to 10 bar approx.)

6 What are factors to be considered to design a hydraulic system?

Answer: Size, Temperature, Application, Media, and Pressure all must be taken into consideration..

7 What are the components of a hydraulic system?

  • Reservoir. ...
  • Filters. ...
  • Shut Off Valves. ...
  • Control Valves. ...
  • Pressure Relief Valve. ...
  • Hydraulic Fuses. ...
  • Accumulators.

8 What is a hydraulic system consist of?

The major components that make up a hydraulic system are the reservoir, pump, valve(s), and actuator(s) (motor, cylinder, etc.).

9 What are the components of the reservoir?

A reservoir system has three main components: a reservoir, an aquifer, and a transition zone (interface) between the two. A reservoir is a porous and permeable rock saturated with oil or gas in buoyancy pressure equilibrium with a free water level

Design of air distribution in a pneumatic system

1 Explain the simple pneumatic system.

A pneumatic system is a collection of interconnected components using compressed air to do work for automated equipment.

3 List the different pneumatic systems used in industries.

Processing industries, such as chemical, petrochemical, food processing, textiles, paper, etc. Used in the brake system of automobiles, railway coaches, wagons, and printing presses. The application of Pneumatics systems is widely in industrial robots.

4 What is the difference between the hydraulic system and a pneumatic system?

  • The main difference between these two is, Hydraulic systems use liquids like water and oil to transmit power.
  • Where pneumatic systems use air to transmit power. In hydraulics, liquids are relatively incompressible.

6 What are the components of the pneumatic system?

  • Air Compressor. As an air exhausting mechanism, this pneumatic equipment component sucks in outside air compresses it and harnesses the air for use in your process.
  • Pneumatic Cylinders.
  • Pneumatic Fittings.
  • Tubing.
  • Pneumatic Valves.

7 What is a pneumatic system consist of?

A method of generating compressed air to power the system.

9 What are the air properties?

The properties of air are:

  • Air takes up space.
  • Air has mass.
  • Air is affected by heat.
  • Air exerts pressure.
  • Air can be compressed.
  • Air is affected by altitude.
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