Review Questions

REVIEW QUESTIONS

1. (a) Mention the role of a pump in a hydraulic system.

[Ans. Refer Section 4.1.1]

( b) How can you classify pumps?

 [Ans. Refer Section 4.3]

2. Classify the positive displacement pumps.

 [Ans. Refer Section 4.3]

3. Explain how positive displacement pumps build pressure compared to rotodynamic pumps. What are the advantages of positive displacement pumps?

 [Ans. Refer Section 4.5]

4. Explain the constructional features and working principles of external gear pump with neat sketches. Also determine its theoretical discharge and performance measures. 

 [Ans.  Refer Section 4.7]

5. How does an internal gear pump differ from an external gear pump?

 [Ans. Refer Section 4.8] 

6. Write short notes on lobe pump.

[Ans. Refer Section 4:9]

7. Describe the constructional features of screw pumps.

[Ans. Refer Section 4:11]

8. Explain with suitable sketch the working of vane pump.

 [Ans. Refer Section 4,13]

9. Explain with suitable sketch the working of unbalanced vane pump.

 [Ans. Refer Section 4:13] 

10. How is the capacity of a variable displacement vane pump is adjusted? Explain with a diagram. (or) Draw a neat sketch of variable discharge axial flow piston pump. Also explain its construction. 

 [Ans. Refer Section 4.14]

11. Describe the working principle of pressure-compensated variable displacement vane pump. 

[Ans. Refer Section 4.14] 

12. Enumerate the working principle of balanced vane pump with neat sketch. Also write the advantages and disadvantages.

 [Ans. Refer Section 4.15] 

13. Using a neat sketch explain the construction and operation of an axial piston pump of swash plate type. 

[Ans. Refer Section 4.17.3] 

14. Explain the construction and working of bent axis type piston pump with neat sketch.

 [Ans. Refer Section 4.18]

15. Explain with suitable sketch the working of radial piston pumps.

 [Ans. Refer Section 4.19]

16. How will you measure the pump performance? Explain each with suitable examples. 

[Ans. Refer Section 4.20]

17. Write an engineering brief about the following :

(i) Pump characteristic curves; 

(ii) Pump cavitation;

(iii) Pump noise, and

 (iv) Pump selection.

 [Ans. Refer (i) Section 4.21; (ii) Section 4.22.3; (iii) Section 4.22.1; (iv) Section 4.23]

18. What are the factors to be considered in selection of a pump?

 [Ans. Refer Section 4.23]

PROBLEMS FOR PRACTICE

1. A positive displacement pump has an overall efficiency of 88% and a mechanical efficiency of 94%. Find its volumetric efficiency. [Ans. 93.62%]

2. A hydraulic system working at a pressure of 100 bars has flow rate of 1.5 Lps, calculate the hydraulic power would a pump produce? 

[Hint: Power (W) = P (N/m2) × QA (m3/s)]

[Ans. 15 kW]

3. A gear pump has a 70 mm outside diameter, a 50 mm inside diameter, and a 25 mm width. If the volumetric efficiency is 88% at rated pressure, what is the corresponding flow rate in units of Lpm. The pump speed is 1200 rpm. 

[Ans. 49.76 Lpm]

4. Calculate the volumetric efficiency of a gear pump for the following specifications: Module of gear teeth = 6 mm; Number of teeth in follower = 16; Gear width = 25 mm; Pressure angle = 20°; Pump speed = 1400 rpm; Flow rate = 125 Lpm. 

[Ans. 88.8%]

5. A vane pump has a rotor diameter of 60 mm, a cam ring diameter of 90 mm, and a vane width of 50 mm. If the eccentricity is 10 mm, determine the volumetric displacement. 

[Ans. 117.81 cm3]

6. Find the flow rate in units of Lpm that an axial piston pump delivers at 1200 rpm. The pump has seven 20 mm diameter pistons arranged on a 150 mm diameter piston circle. The offset angle is set at 12° and the volumetric efficiency is 95%. [Ans. 79.93 Lpm]

7. A radial piston pump has the following specifications: Number of plunger = 7; Diameter of plunger 25 mm; Maximum eccentricity = 10 mm; Pump speed = 1200 rpm; Maximum pressure = 150 bars.

Calculate (i) the theoretical discharge, (ii) Actual discharge, (iii) Theoretical power required to operate the pump, and (iv) Actual power delivered to pump. The volumetric and mechanical efficiencies of the pump are 92% and 82% respectively.

[Hint: QT = 0.5 e Ÿ лd2 Ñ; QA = QT × ηvol ; Theoretical power = P (N/m2) × QT  (m3/s); Actual power = Theoretical power ×ηmech]

[Ans. (i) 82.47 Lpm; (ii) 75.87 Lpm; (iii) 20.62 kW; (iv) 16.91 kW] 

8. A pump has a displacement volume of 0.0819 × 10-3 m3. It delivers 0.0758 m3/min at 1000 rpm and 67 MPa. If the prime mover input torque is 100 N-m,

(a) What is the overall efficiency of the pump, and

(b) What is the theoretical torque required to operate the pump. 

 [Hint: Refer Example 4.8] 

[Ans. (a) 80.83%; (b) 87.33 N-m]

9. 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. 

 [Hint: Refer Example 4.8]