B.E./B.Tech. Degree Examination, November/December 2006

B.E./B.Tech. Degree Examination, November/December 2006 

Sixth Semester - Mechanical Engineering (Regulation 2004) 

ME 1305-HYDRAULIC AND PNEUMATIC CONTROLS

Time: Three hours

Answer ALL questions.

Part A-(10 x 2 = 20 marks)

Maximum: 100 marks

1. Differentiate pressure compensated and non-pressure compensated pumps.

Ans. Refer Chapter 6, Q. No. 25, Two Marks Q&A, Page No. 6.47.

2. Draw the hydraulic symbols for a pressure-temperature compensated flow control valve and bidirectional motor.

Ans. Refer Chapter 6, Q. No. 23 & 33, Two Marks Q&A, Page Nos. 6.51 & 6.52.

3. What is "meter-out” circuit? What are its limitations?

Ans. Refer Chapter 6, Q. No. 23, Two Marks Q&A, Page No. 6.2.

4. Define pressure override' in pressure control valves.

Ans. Refer Chapter 6, Q. No. 21, Two Marks Q&A, Page No. 6.49.

5. Highlight the need of using an accumulator in hydraulic circuits. 

Ans. Refer Chapter 9, Q. No. 5, Two Marks Q&A, Page No. 9.34.

6. State the role of PLC in fluid power industry.

Ans. Refer Chapter 15, Q. No. 18, Two Marks Q&A, Page No. 15.29.

7. Draw a circuit to automatically reciprocate a pneumatic cylinder using a pressure switch.

Ans. Refer Chapter 14, Section 14.5.1, Page No. 14.9.

8. What is twin pressure valve?

Ans. Refer Chapter 6, Q. No. 24, Two Marks Q&A, Page No. 6.50.

9. How do you rate a compressor?

Ans. Refer Chapter 11, Q. No. 8, Two Marks Q&A, Page No. 11.21. 

10. What are the important components of a hydraulic power pack?

Ans. Refer Chapter 16, Q. No. 7, Two Marks Q&A, Page No. 16.40. 

Part B - (5 × 16 = 80 marks)

11. (a) (i) What are the advantages of oil hydraulic systems over other methods? 

Ans. Refer Chapter 1, Section 1.7.5, Page No.1.14.

 (ii) A gear pump has a displacement of 60,000 m3. It delivers 100 liters per minute at 1440 rpm and 8 N/mm2. If the prime mover input torque is 75 N.m.,

(1) Find overall efficiency of the pump.

(2) The theoretical torque required to operate the pump.

Also derive the equations for the volumetric discharge, efficiency and torque.

Ans. Refer Chapter 4, Example 4.8, Page No. 4.41.

[OR]

(b) With a neat sketch explain the principle, construction, working, advantages, limitations and applications of a non-pressure compensated reciprocating vane pump. 

Ans. Refer Chapter 4, Section 4.12, Page No.4.16. (16)

12. (a) (i) Explain with a circuit how in a shaping operation a fast approach, slow feed and rapid return can be achieved.

Ans. Refer Chapter 16, Section 16.3, Page No.16.2.

 (ii) Explain with a circuit the technique of how a punching operation can be achieved. 

Ans. Refer Chapter 16, Section 16.7, Page No.16.8.

[OR]

 (b) Explain with suitable circuits how the following requirements can be achieved in an industry.

(i) Safety of the operator by using two handed push buttons.

(ii) The system can be protected from high pressures.

Ans. (i) Refer Chapter 8, Section 8.13.3, Page No.8.21.

(ii) Refer Chapter 8, Section 8.13.2, Page No.8.20.

13. (a) Designa punching press with five working stations operated by five single acting cylinders connected to an intensifier. The cylinders require 20 mm travel and used to punch 20mm diameter holes on sheet metals of 5 mm thick of mild steel whose strength is 360 MPa. Determine the oil pressure of the hydraulic system and length of the intensifying cylinder if the load piston area is 20000 mm2, ram piston area and small piston area of the intensifier are 15000 mm2 and 900 mm2. 

Ans. Refer Chapter 9, Example 9.10, Page No.9.28.

[OR]

 (b) Design a car crushing system. The crushing force required is such that a 20 cm diameter cylinder is required at a working pressure of 130 kg/cm2. Time for crushing is about 10 sec and the stroke required to flatten the car is 300 cm. Compare the power requirements of a circuit without and with accumulator.

Accumulator details: It is a gas loaded accumulator.

Time taken for charging = 6 min

Initial pressure of charging (precharged), P1 = 100 kg/cm2

Charged pressure of accumulator, P2 = 225 kg/cm2

Minimum pressure for crushing, P3 = 130 kg/cm2

Ans. Refer Chapter 9, Exercise 3, Page No.9.37. 

14. (a) (i) Describe the operation of an “FRL” trio unit. 

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

(ii) Explain with ANSI symbols.

(1) All the types of actuators used in pneumatics.

(2) Quick exhaust valve and silencer.

Ans. (1) Refer Chapter 12, Sections 12.7-12.9, Page No. 12.10.

(2) Refer Chapters 12, Section 12.4.4, Page Nos. 12.7.

[OR]

 (b) (i) Highlight the advantages of an air over oil circuit and explain it with a suitable application.

Ans. Refer Chapter 9, Section 9.13.2, Page No.9.31.

(ii) Brief on a electro hydraulic servo system used in industries. 

Ans. Refer Chapter 6, Section 6.25, Page No.6.32.

15. (a) Three pneumatic cylinders A, B, C are used in an automatic sequence of operation. A cylinder extends, B cylinder retracts, C cylinder retracts and then A cylinder retracts, C cylinder extends and B cylinder extends. Develop pneumatic circuits by cascade method. Sketch also travel-step diagram and explain briefly.

Ans. Refer Chapter 13, Example 13.1, Page No.13.19.

[OR]

 (b) (i) Brief on the methodology adopted to install and maintain a pneumatic power pack.

Ans. Refer Chapter 17, Sections 17.5 & 17.6, Page No. 17.14.

 (ii) Writé short notes on low cost automation.

Ans. Refer Chapter 16, Section 16.15, Page No.16.30.