# Pneumatic Circuit Design | Interview Question and Answers

Pneumatic Circuit Design | Interview viva, oral  Question and Answers

1. What is the main advantage of hydro pneumatics?

The hydropneumatic systems use air and oil. By the use of both media, the quick action of air and smooth high pressure action of oi I both can be achieved.

2. Name the different hydropneumatic appliances.

(i) Air-oil reservoir (ii) Air-oil cylinder (iii) Air-oil intensifier.

3. What do you mean by logic control?

The logic control is a control based on logic functions like AND, OR, NOT etc. The components of logic control are sensors and switching elements called binary elements, i.e. at any moment they can be in one of the two states. “ON-OFF”.

4. Name the different pneumatic position sensors.

(i) Pneumatic limit valves (ii) Back pressure sensor (iii) Proximity sensor (iv) Gap sensor or Interruptible jet sensor (v) Limit switch.

5. What are moving part logic elements (MPL)?

The MPL elements are miniature pneumatic elements. These elements are available as AND, OR, NOT logic elements. The elements use moving parts such as diaphragms, springs, disk, balls, poppets.

6. What is Fluidics?

Fluidics is fluid logics. It is based on jet interaction. Fluidic elements have no mechanical moving parts.

7. What are the advantages of fluidic elements?

(i) A wear and tear of elements. (ii) No actuating force needed. (iii) Very little space needed for mounting. (iv) Quite insensitive to temperature, vibration, shock, electric noise and radiation.

8. Draw the symbol for fluidic OR element and write its truth table.

10. Name the common methods used for designing logic circuits?

1. Classic method 2. Cascade method 3. Step counter method 4. KV map method 5. Combinational circuit design.

11. What is a step counter?

A step counter is a digital modular counter constructed from stepping units. A stepping unit is built from memory valve and a preswitched AND valve with two inputs.

12. What is the difference between pressure switch and a temperature switch?

Pressure switches open or close contacts based on the system pressure. Temperature switches senses change in temperature and open or close contacts when a predetermined temperature is reached.

13. How does a limit switch differ from a push button switch?

Push button switches are momentary switches. They make or break contact only as long as they are held pressed. But limit switches make or break contact permanently when they are actuated.

14. What is an electrical relay?

Electrical relay is a switch whose contacts open or close when its coil is energised. Relays are used for energising and de-energising solenoids.

15. What is the purpose of an electrical timer?

Timers are used to control the time duration of a working cycle. In this way, a dwell can be provided when needed.

16. What is a ladder diagram?

The ladder diagram is a representation of hardware connections between switches, relays and solenoids etc., which constitute the basic components of an electrical control system. The left leg of the ladder connected to the power and the right to the ground.

17. What is the advantage of using microelectronic control for fluid power compared to electro-mechanical control?

When the sequence changes, the hardwired electro-mechanical has to be changed. This is expensive, but microelectronic control is programmable. So when the sequence changes, the program only has to be changed.

18. What is a Programmable Logic Controller (PLC)?

Programmable Logic Controller is defined as a digital electronic device that uses a programmable memory to store instructions such as logic, sequencing, timing, counting and arithmetic to control machine or processes.

19. What are the basic elements of PLC?

(i) Central processing unit with an associated memory (ii) Input modules (iii) Output modules.

20. What are the various approaches for entering the program in PLC?

(ii) Low-level language based on Boolean expressions
(iii) Functional blocks (iv) High-level languages.

21. Explain why interfacing is necessary in a microprocessor control of fluid power?

Microprocessors usually works with different levels of voltages and currents than those used by sensors and actuators. So an interface is needed to connect the items which are not directly compatible.

22. Compare PLC and a computer on the basis of fluid power applications.

PLC can be interfaced with hundreds of input and output lines. PLCs are designed for industrial environments where they may be exposed to heat, humidity, and corrosive atmosphere. Microcomputers are used where the input and output lines are limited and more data processing is required.

23. What is the important requirement to get a maximum trouble-free life from fluid power systems?

(i) Properly installed equipments (ii) Properly trained personnel
(iii) Planned bolts preventive maintenance
(iv) Effective troubleshooting.

24. What is the meaning of the term “troubleshooting”?

The tenn troubleshooting means an organised and systematic study of the problem and a logical approach to the difficulty faced in the system.

25. List five things that can cause a noisy pump.

(i) Misalignment of pump and prime mover (ii) Air remains in pump casing (iii) Pump bolts very loose (iv) Very high viscosity of oil (v) Pump running too fast.

26. List three causes for low or erratic pressure in a hydraulic system.

(i) Very low relief valve setting
(ii) Leakage of pump delivery within the system
(iii) Pump slipping its entire volume.

27. If a pneumatic cylinder has erratic motion, name the causes.

(i) Valve sticking or binding (ii) Cylinder sticking or binding.

28. What is a tree-branching chart?

Tree-branching chart is a chart used to simplify the troubleshooting process. This chart asks a question which has only two possible answers-Yes or No. The answer determines the next step to be taken in fault analysis. This chart helps to develop a logical and rapid approach to fault diagnosis.

29. Define Low-Cost Automation and what are its features?

Low-cost automation is defined as a technology that creates some degree of automation around the existing equipment, tools and methods, using mostly the standard equipment available in the market.

The features of LCA are,
(i) The automation of small to medium scale industries can be made viable.
(ii) Since it is built using the existing resources, in a systematic way,
the investment risks are low.
(iii) Labour productivity can be enhanced substantially.