B.E./B.Tech. Degree Examination, May/June 2012

B.E./B.Tech. Degree Examination, May/June 2012

Fifth Semester-Mechanical Engineering (Regulation 2008)

ME 2305/ME $5/ME 1305/10122/ME 506 – APPLIED HYDRAULICS AND PNEUMATICS

 Time: Three hours

Maximum: 100 marks

Answer ALL questions. 

Part A - (10 × 2 = 20 marks)

1. Compare hydraulic and pneumatic drives for automation.

Ans. Refer Chapter 1, Q. No. 18, Two Marks Q&A, Page No. 1.25.

2. State Pascal's law with an industrial example.

Ans. Refer Chapter 3, Q. No. 2, Two Marks Q&A, Page No. 3.28.

3. What are positive displacement pumps?

Ans. Refer Chapter 4, Q. No. 6, Two Marks Q&A, Page No. 4.45.

4. Mention the significance of a telescopic cylinder with an industrial example. 

Ans. Refer Chapter 5, Q. No. 14, Two Marks Q&A, Page No. 5.32.

5. Identify the following elements, represented in Fig.2 and Fig.3.

Ans. Refer Chapter 6, Q. No. 15, Two Marks Q&A, Page No. 6.48.

6. List any four basic types of electric switches used in electrically controlled fluid power Postek circuits.

Ans. Refer Chapter 14, Q. No. 2, Two Marks Q&A, Page No. 14.16.

7. ‘Quick exhaust valve is used to increase the piston speed of spring return single acting pneumatic cylinder' - Justify.

Ans. Refer Chapter 12, Q. No. 5, Two Marks Q&A, Page No. 12.16.

8. State any four advantages of pneumo-hydraulic circuits.

Ans. Refer Chapter 8, Q. No. 16, Two Marks Q&A, Page No. 8.38. 

9. List the three types of proportional control valves.

Ans. Refer Chapter 9, Q. No. 45, Two Marks Q&A, Page No. 6.53. 

10. State any four common causes for hydraulic system breakdowns. 

Ans. Refer Chapter 17, Q. No. 3, Two Marks Q&A, Page No. 17.25. 

PART B - (5 × 16 = 80 marks)

11. (a) (i) Explain in detail an eight desirable properties of a good hydraulic fluid. 

Ans. Refer Chapter 2, Section 2:5, Page No.2.12.

(ii) Explain the advantages and limitations of using petroleum based hydraulic oils.

Ans. Refer Chapter 2, Section 2.6.1, Page No.2.14.

[OR]

 (b) (i) Hydraulic oil of kinematic viscosity 0.9 stokes, flows through a 35 mm diameter pipe at a velocity of 4 m/s for a length of 100 m. Find the head loss due to friction (in units of bar). Assume specific gravity of oil as 0.90. 

Ans. Refer Chapter 3, Example 3.13, Page No.3.24.

 (ii) State the significance of ‘K-factor' in determining the losses in valves and fittings. Determine the head loss (in units of bar) across a 40 mm wide open gate valve, when hydraulic oil of specific gravity 0.9 flows through it at a rate of 0.015 m3/s. The K-factor for wide open gate valve is 0.19.

Ans. Refer Chapter 3, Section 3.15 & Example 3.4, Page Nos.3.17 & 3.24.

12. (a) (i) With a neat sketch, explain the construction and working principle of an (10) external gear pump.

Ans. Refer Chapter 4, Section 4.7, Page No.4.8.

(ii) A pump having a displacement of 80 cm3, delivers oil at the rate of 1.25 lps at 1200 rpm and 75 bar. If the prime mover input torque is 90 N-m, calculate the overall efficiency of the pump and the theoretical torque required to operate the pump. 

Ans. Refer Chapter 4, Exercise 9, Page No.4.52.

[OR]

(b) With a neat sketch, explain the construction and cushioning mechanism in a cylinder.

Ans. Refer Chapter 5, Section 5.5, Page No.5.6.

(ii) With a neat sketch, explain the working principle of balanced Vane pump. 

Ans. Refer Chapter 4, Section 4.15, Page No.4.19.

13. (a) Write short note on:

(i) Direct acting pressure reducing valve

Ans. Refer Chapter 6, Section 6.17, Page No.6.23.

(ii) Pilot operated sequence valve.

Ans. Refer Chapter 6, Section 6.18, Page No.6.23.

[OR]

(b) (i) List the advantages and limitations of a spring loaded accumulator. 

Ans. Refer Chapter 9, Section 9.3, Page No.9.4.

 (ii) A pump/accumulator power pack is to supply the fluid flow demanded by a hydraulic system as shown in Fig.4. The system working pressure is 125 bar and the maximum pressure at the accumulator is 200 bar. Assuming the accumulator precharge pressure is 90% of its maximum working pressure, determine

(1) the actual pump delivery required,

(2) the maximum volume of fluid to be stored in the accumulator, and

(3) the accumulator volume, assuming an isothermal charge and discharge of the accumulator.

14. (a) With a neat sketch, explain the working principle of a screw compressor.

Ans. Refer Chapter 11, Section 11.4, Page No.11.5.

 (ii) With neat sketches, explain the importance of a filter and regulator unit in a pneumatic system.

Ans. Refer Chapter 11, Section 11.10, Page No.11.15.

[OR]

 (b) Valve bodies are to be marked with the letters. P, A, B and R (Fig.Error! Reference source not found.). The valve bodies are placed in the holder manually. Stamping cylinder A stamps the letter in the body and returns. Cylinder B pushes the parts from the holder into a basket and returns to its initial position. Design a pneumatic sequential circuit for the above operation using cascade method.

15. (a) (i) Explain the hydromechanical servo valve with an industrial example. 

Ans. Refer Chapter 6, Sections 6.24 & 8.19, Page Nos.6.30 & 8.32. 

(ii) Write short notes on Bistable Flip-Flops.

Ans. Refer Chapter 15, Section 15.4.1, Page No.15.4.

 (b) (i) Two pneumatic cylinders are used to transfer parts from a magazine onto a chute (Fig.Error! Reference source not found.). When a pushbutton is pressed, cylinder (A) extends, pushing the part from the magazine and positions it in preparation for transfer by cylinder (B) onto the outfeed chute. Once the part is transferred, the cylinder (A) retracts, followed by the cylinder (B). Sketch the ladder (10) logic diagram for the above operation.

Ans. Refer Chapter 13, Example 13.6, Page No.13.24.

 (a) With a block diagram, explain the major units of a PLC. 

Ans. Refer Chapter 15, Section 15.9, Page No.15.21.