PNEUMATIC SYSTEM INTERVIEW QUESTIONS AND ANSWERS
1. Mention at least five applications in which compressed air is used?
2. What is the compressed air pressure used in the spraying of paint in Gravity feed spray
gun? What precautions you must take while using the compressed air for spray gun
application?
3. Pneumatic cylinders are used to convert the pressure energy of the compressed air to
mechanical motions. However, the compressed air is also used directly, for example,
inflating a car tyre. Write at least two more such usages of the compressed air.
4. Besides compressed air, what other medium can be used for obtaining linear or rotary
motion?
5. Is it possible to get a linear motion using an electric motor? If yes, briefly outline the
method.
6. What is the function of an intercooler in a two-stage compressor?
7. Is it advisable to tap the compressed air directly from a rotary compressor? Why?
8. What is the need of a pressure switch in a compressor, when there is a regulator in the
air preparation system?
9. If you are buying a compressor from a manufacturer, how would you specify the several
parameters of the compressor?
10. Present-day users are not keen on using a lubricator in the air-preparation system. Why?
11. If you are buying a compressor for a hill station, what factor would you stress to the
manufacturer?
12. What is the difference between signal air and control air?
13. What are the ways by which a 3/2 pneumatic direction control valve can be activated?
14. What are the ways by which a 5/2 pneumatic direction control valve can be activated?
15. A double-pilot valve has a memory. Explain?
1. Applications of Compressed Air
Compressed air is widely used in various industries and applications, including:
- Pneumatic tools: Drills, hammers, and grinders.
- Paint spraying: Automotive and industrial painting.
- Material handling: Conveying materials like grains or powders.
- Cooling systems: Air jet cooling in machinery.
- Inflating tires: Car, bicycle, and aircraft tires.
2. Compressed Air Pressure in Gravity Feed Spray Gun
- Pressure: The compressed air pressure used in gravity feed spray guns typically ranges between 20 to 50 PSI.
- Precautions:
- Ensure the pressure is within the manufacturer's recommended range.
- Use proper personal protective equipment (PPE) like masks and goggles.
- Avoid spraying in poorly ventilated areas to prevent inhalation of fumes.
- Check for leaks in hoses and connections.
3. Other Usages of Compressed Air
Apart from inflating tires, compressed air is used for:
- Cleaning: Blowing off dust and debris from equipment.
- Cooling: Air cooling of electronic components or machinery.
4. Alternative Mediums for Linear or Rotary Motion
Other mediums include:
- Hydraulics: Using pressurized liquids.
- Electric systems: Utilizing motors or actuators.
5. Linear Motion Using an Electric Motor
Yes, linear motion can be achieved using an electric motor through:
- Lead screws or ball screws: Motors drive these screws, converting rotary motion into linear motion.
- Linear actuators: These directly produce linear movement using electric motors.
6. Function of an Intercooler in a Two-Stage Compressor
An intercooler reduces the temperature of the compressed air between stages, which:
- Improves efficiency by reducing the work needed for further compression.
- Prevents overheating and damage to the compressor.
7. Tapping Air Directly from a Rotary Compressor
It is not advisable to tap compressed air directly from a rotary compressor because:
- The air may contain oil, water, or contaminants.
- Proper air preparation, including filtration and drying, is essential to ensure quality.
8. Need for a Pressure Switch in a Compressor
A pressure switch:
- Automatically starts or stops the compressor based on the set pressure range.
- Prevents over-pressurization, which a regulator in the air preparation system cannot control.
9. Parameters for Specifying a Compressor
When buying a compressor, specify:
- Pressure range: Maximum and minimum pressures.
- Flow rate: Cubic feet per minute (CFM).
- Type: Rotary, reciprocating, etc.
- Power source: Electric, diesel, or petrol.
- Operating environment: Temperature and humidity conditions.
10. Declining Use of Lubricators in Air-Preparation Systems
Modern systems avoid lubricators because:
- Many pneumatic tools are now designed as lubrication-free.
- Excessive lubrication can contaminate processes (e.g., in food or pharmaceutical industries).
11. Consideration for Compressors in Hill Stations
Stress the following factors:
- Altitude: Higher altitudes reduce air density, affecting compressor performance.
- Cooling system: Ensure it is suitable for lower ambient temperatures.
12. Difference Between Signal Air and Control Air
- Signal air: Used to transmit signals for controlling operations.
- Control air: Directly operates actuators or control devices.
13. Activation of a 3/2 Pneumatic Direction Control Valve
A 3/2 valve can be activated by:
- Manual actuation (push buttons).
- Mechanical actuation (cams or levers).
- Pneumatic actuation (pilot air).
- Electrical actuation (solenoids).
14. Activation of a 5/2 Pneumatic Direction Control Valve
A 5/2 valve can be activated by:
- Electrical solenoids.
- Pneumatic pilots.
- Mechanical levers or rollers.
15. Memory in a Double-Pilot Valve
A double-pilot valve has a memory because:
- It retains its last actuated position even after the control signal is removed.
- This feature is useful in maintaining the state of an operation during power or signal loss.
2. Do you think that the direction control valves can be used for signal air as well as for
control air?
3. What do you mean by a normally-closed direction control valve? What mechanism would
make the valve to stay in a continuously-open or closed position?
4. In the numbering system, what number is allotted to the flow control valve located closer
to the cylinder ports?
5. Identify the number of air connections that a 5/2 valve and a 3/2 valve direction control
valve have?
6. In a circuit, what does the number 2.1 signify to you?
7. What are the alternate names given to an AND gate and an OR gate?
8. Is it possible to use both AND and OR gates in a single circuit?
9. What is the essential difference in the function of an AND gate as compared to an OR
gate?
10. In an OR gate, in case, two input signals are given, will there be an output signal? Mention
a practical situation or an application when an OR gate is needed in a pneumatic circuit.
11. How many input signals and output signal connections are available in AND gate and OR
gate valves?
1. Differentiation Between Control Air and Signal Air
- Control Air: Air used to operate actuators or move mechanical components directly.
- Signal Air: Air used to transmit commands or signals to control devices without directly operating actuators.
2. Can Direction Control Valves Be Used for Both?
Yes, direction control valves can be used for both signal air and control air, but the size, flow capacity, and application requirements may differ. Signal air typically uses smaller valves due to lower flow demands.
3. Normally-Closed Direction Control Valve
- Definition: A valve that remains closed under normal conditions and only opens when actuated.
- Mechanism: Springs or mechanical stops keep it closed, while pneumatic, electrical, or manual actuation opens it.
4. Numbering System for Flow Control Valves Near Cylinder Ports
In the numbering system, 1.2 or 2.2 is commonly allotted to flow control valves near cylinder ports, depending on the circuit design.
5. Number of Air Connections
- 5/2 Valve: Five ports and two positions.
- 3/2 Valve: Three ports and two positions.
6. Significance of 2.1 in a Circuit
2.1 indicates the signal path from port 2 to port 1 in a circuit, often showing a transition or connection in a specific direction.
7. Alternate Names for AND and OR Gates
- AND Gate: Known as a Series Valve.
- OR Gate: Known as a Parallel Valve.
8. Using AND and OR Gates in a Single Circuit
Yes, it is possible to use both gates in a single circuit to create complex logic, such as enabling an actuator only when multiple conditions (AND) or any one condition (OR) is satisfied.
9. Difference Between AND and OR Gates
- AND Gate: Requires all input signals to be present simultaneously to produce an output.
- OR Gate: Produces an output if at least one input signal is present.
10. OR Gate Output with Two Input Signals
Yes, an OR gate will produce an output signal if either or both input signals are present.
- Application: Used in safety systems where multiple emergency stop signals can trigger a shutdown.
11. Connections in AND and OR Gate Valves
- AND Gate: Two input signal connections and one output signal connection.
- OR Gate: Two input signal connections and one output signal connection.