Pneumatics and Hydraulics MCQ Quiz - Objective Question with Answer for Pneumatics and Hydraulics - Download Free PDF

Explanation:

4/2 Valve

• A 4/2 valve is a type of directional control valve commonly used in hydraulic and pneumatic systems. The numbers 4/2 denote that the valve has four ports and two positions. These valves are essential components in systems where the control of fluid flow direction is necessary for the operation of actuators such as cylinders or motors.
• The 4/2 valve operates by shifting its internal mechanism to connect different ports, thus controlling the direction of fluid flow. The two positions of the valve determine which ports are connected and which are blocked. Typically, these positions are controlled by a solenoid, a lever, or pneumatic pilot pressure. In one position, the valve directs the fluid to one side of the actuator, and in the other position, it reverses the flow, directing the fluid to the opposite side.

Advantages:

• Provides precise control over the direction of fluid flow.
• Can be easily automated using solenoids or other control mechanisms.
• Reliable operation with minimal maintenance requirements.

Disadvantages:

• More complex and expensive compared to simpler valves.
• Potential for internal leakage if not properly maintained.

Applications: 4/2 valves are used in a wide range of applications, including industrial machinery, automotive systems, and other equipment where directional control of hydraulic or pneumatic actuators is required.

Explanation:

Centrally Closed 4-Way 3-Position Solenoid Operated D. C. Valve

• A centrally closed 4-way 3-position solenoid operated directional control (D. C.) valve is a type of hydraulic or pneumatic valve that controls the direction of fluid flow.
• It features four ports and three positions, with the center position being closed.
• It is operated electrically by a solenoid, which provides the actuation force to shift the valve positions.
• In this type of valve, the solenoid coil is energized to move the spool, which directs the fluid flow to different ports.
• When the solenoid is de-energized, the spool returns to its central position, blocking all ports and stopping the flow of fluid. The three positions typically include:
  • Position 1: Directs fluid from the pump port to an actuator port and returns fluid from the other actuator port to the tank.
  • Position 2: Central position where all ports are closed, stopping the fluid flow.
  • Position 3: Directs fluid in the reverse direction compared to Position 1.

Advantages:

• Precise control of fluid flow direction, enabling accurate operation of hydraulic or pneumatic systems.
• Electrical operation via solenoids allows for easy integration with automated systems and remote control.
• When in the central position, all ports are closed, which can be useful for holding a load or stopping a motion in mid-position.

Disadvantages:

• More complex than simpler valve types, requiring electrical connections and solenoid maintenance.
• Potential for solenoid failure, which could lead to loss of control over the fluid flow.

Applications: Centrally closed 4-way 3-position solenoid operated D. C. valves are commonly used in hydraulic and pneumatic systems for industrial automation, machinery control, and various fluid power applications where precise control of actuator movement is required.

Explanation:

Air compressor:

• Air compressors are a type of machine tool and they work great with other power tools too.
• It basically provides other tools the ability to function and the power to do household as well as industrial improvement projects and installations.
• In order for tools to function their best, the air compressor must be working at its optimum power and efficiency and that means that the parts of an air compressor must be working 100% of the time to make sure the work is done.

• Motor
• Tank
• Pressure switch
• Drain valve
• Pressure gauge
• Inlet port
• Inlet valve assembly
• Cooling fins
• Discharge Port
• Discharge valve assembly
• Air filter
• Safety valve
• Regulator
• Check valve/Non-return valve (NRV) and unloader tube
• Compressor fan

• The pressure switch automatically shuts down the motor when the receiver reaches the factory-set limit.
• Once the pressure level drops to a pre-set level then the pressure switch restarts the motor, therefore, resuming the pumping of air by the compressor.
• We can also call this an emergency switch that regulates how much pressure in the tank can take.

Explanation:

Pascal's Law:

• It states that the pressure exerted on a liquid is transmitted equally in all directions.
• Thus if a small amount of pressure is exerted on a smaller piston, a higher force can be attained at the larger piston, since the pressure is equally applied on a larger area.

Additional Information
Archimedes’ Principle:

• It states that the upward buoyant force that is exerted on a body immersed in a fluid, whether partially or fully submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.

Explanation:

Electro-pneumatics:

• Electro-pneumatic control consists of electrical control systems operating pneumatic power systems.
• In this, solenoid valves are used as interfaces between the electrical and pneumatic systems.
• Devices like switches are used as feedback elements. In electro pneumatics, the signal medium is the electrical signal either AC or DC source is used.
• The working medium is compressed air.

Basic electrical devices:

Basic electrical devices commonly used in the control of fluid power systems are:

• Manually-actuated push button switches
• Limit switches
• Pressure switches
• Solenoids
• Relays
• Temperature switches

Relay:

• A relay is an electromagnetically actuated switch.
• It is a simple electrical device used for signal processing.
• Relays are designed to withstand heavy power surges and harsh environmental conditions.
• When a voltage is applied to the solenoid coil, an electromagnetic field is developed.
• This causes the armature to be attracted to the coil core.
• The armature actuates the relay contacts, either closing or opening them, depending on the design.
• A return spring returns the armature to its initial position when the current to the coil is interrupted.

Explanation:

Desirable qualities of an actual working substance for transmitting load in a hydraulic piston: 

• Wear resistance
• Negligible compressibility

\({\rm{C\;}} = {\rm{\;}}\frac{1}{{\rm{K}}}{\rm{\;}} = {\rm{\;}}\frac{{\Delta {\rm{V}}/{\rm{V}}}}{{\Delta {\rm{P}}}}\)

• Infinite bulk modulus 

​Bulk Modulus is reciprocal of compressibility.

Hydraulic fluid is nearly incompressible.

Explanation:

An actuator is an element of hydraulic and pneumatic systems where work is done. In this, the basic elements of the system are the power source, control valves and actuators which is usually a cylinder.

Explanation:

• Pneumatic technology deals with the study of behavior and applications of compressed air.
• Pneumatic systems use air as the medium which is abundantly available and can be exhausted into the atmosphere after completion of the assigned task.
• The compressor is the power source in the pneumatic system.

Explanation:

• One of the most commonly used Gate driving mechanisms is the hydraulic cylinders.
• Hydraulic cylinders are operated by oi pressure supplied by a pumping unit.
• It is classified into two types:
  • Single cylinder 
  • Double cylinder
• The choice of the cylinder is determined by the force required to move the load and the speed required.
• Hydraulic cylinders are capable of much larger forces then pneumatic cylinders.
• The force produced by a cylinder is equal to the cross-sectional area of the cylinder multiplied by the working pressure. 
• Therefore, the working pressure of a hydraulic cylinder depends on the diameter of cylinder.

Explanation:

Pascal’s principle: Pascal’s Law is the principle of transmission of fluid pressure.

• It says that "a pressure exerted anywhere in a point of the confined fluid is transmitted equally in all directions throughout the fluid”.

Additional Information

Hydraulic Lift: Given that area of the piston, B is greater than the area of piston A i.e. AA < AB

From Pascal's Law, the pressure inside the liquid will be equal at every place. So the pressure at A and B will be equal.

PA = PB

\(Pressure = {Force\over Area}\)

\( {F_A \over A_A}={F_B \over A_B}\)

\( {m_Ag \over A_A}={m_B g\over A_B}\)

\( {m_Ag \over A_A}={m_B g\over A_B}\)

\( {m_A\over m_B}={ A_A \over A_B}\)

if  AA < AB

then mA < mB

Explanation:

AND Function

• In a pneumatic system, a two pressure-valve or dual-pressure valve works as an AND gate.
• If a compressed air signal is applied to input X and input Y at the same time, this will produce a signal at output Z.

   ​  

• However, if there is no signal, there is also no output signal. 
• If only one input signal is applied, there will be no output signal.

​

• In case of time differences between the input signals, the signal arriving last reaches the output.
• In case of pressure differences between the input signals, the signal with the lower pressure reaches the output. 

Important Points

OR Function

• The single-acting cylinder in Fig can be operated by two different circuits.
• Examples include manual operation and relying on automatic circuit signals, that is, when either control valve or control valve is operated, the cylinder will work.
• Therefore, the circuit in Fig. possesses the OR function. However, if the output of two 3/2 directional control valves is connected through the port of a triode, the air current from the control valve will be released through the exhaust of the control valve, and so the cylinder will not work.
• This problem can be solved by connecting a shuttle valve to the port of the triode.
• The shuttle valve allows fluid flow from one of two sources just like OR logic. The basic structure of a shuttle valve is like a tube with three openings.

Explanation:

• Pneumatic roller lever valves are used to sense the position of parts mechanically within machine automation systems; a moving part passes over the roller and operates the valve.
• It is also used to avoid the overlapping signals in pneumatic systems
• Pneumatic roller lever valves sense moving machine parts, often used for detecting the stroke of pneumatic cylinders, as a limit switch for door or barrier closure, or used to identify the correct placement of components before machine operation.

Explanation:

The study of pneumatic deals with systems operated with air. Pneumatic control systems operate on a supply of compressed air. Advantages of air:

• Air is available everywhere
• Air requires no return valve
• Air is explosion free
• Air is non-pollutant
• Speeds and forces can be varied with pneumatic components.

Explanation:

Pneumatic systems

• The study of pneumatic deals with systems operated with air. 
• Pneumatic control systems operate on a supply of compressed air.

Advantages of air:

• Air is available everywhere
• Air requires no return valve
• Air is explosion free
• Air is non-pollutant
• Speeds and forces can be varied with pneumatic components.

Explanation:

Fluid Link:

• A fluid link is one that is deformed by having an incompressible fluid in a closed vessel and the motion is transmitted through the fluid by pressure, as in the case of a hydraulic press, hydraulic jack, and hydraulic brake.

Rigid Link:

• A rigid link is one that does not undergo any deformation while transmitting motion. Links in general are elastic in nature.
• They are considered rigid if they do not undergo appreciable deformation while transmitting motion, for example connecting rod, crank, tappet rod etc.

Resistant Link:

• A link that is rigid for the purposes it serves.
• Apart from rigid links, there are some semi-rigid links that are normally flexible, but under certain loading conditions act as a rigid link for limited purposes and thus are the resistant link.
• These days resistant links are usually referred to as rigid links.

Flexible Link:

• A flexible link is one which while transmitting motion is partly deformed in a manner not to affect the transmission of motion, for example, belts, ropes, chains, springs, etc.

Floating Link:

• This is a link that is not connected to the frame.