- Minimum speed required for starting a centrifugal pump
- In multistage centrifugal pump− For high head, pumps are coupled in series− For high discharge, pumps are coupled in parallel− Specific speed,
- Priming of centrifugal pump: Priming of a centrifugal pump is defined as the operation in which the suction pipe, casing of the pump and a part of the delivery pipe up to the delivery valve is completely filled with water and air from these parts of the pump is removed.
Example 9.13: A centrifugal pump running at 1,500 rpm has internal and external impeller diameter of 200 and 300 mm, respectively. The vane angles of impeller at inlet and outlet are 25° and 30°, respectively. If water enters the impeller radially and velocity of flow remains constant, determine the work done by the impeller per unit weight of water.
Solution:
Work done by impeller per kg of water per second = 
= 26.1287Nm/s
Example 9.14: A centrifugal pump having internal and external diameter of impeller 150 and 600 mm, respectively, is running at 800 rpm. It has constant velocity of flow of 3 m/s and discharge through pump is 0.03 m3/s. The diameters of suction and delivery pipes are 100 and 75 mm, respectively and suction and delivery heads are 5 and 25 m of water, respectively. If outlet vane angle is 40° and power required to drive the pump is 15 kW, determine (i) vane angle at inlet, (ii) overall efficiency of pump, and (iii) manometric efficiency of pump.
Solution:
Given: D1 = 150mm; D2 = 600mm; N = 800rpm; Vf1 = Vf2 = 3m/s;
Q = 0.03m3/s; ds = 100mm; dd = 75mm; Hs = 5m; Hd = 25m; ɸ = 40; P = 15kW.
Here, subscript o stands for outlet and i stands for inlet
Example 9.15: Following data of a centrifugal pump are given as: Diameter at inlet = 0.5 m; Diameter at outlet = 1.0 m; Speed = 250 rpm; Flow rate = 1,800 l/s; Vane exit angle = 25°; Velocity of flow = 3 m/s; Head = 8 m. Find the least speed to start the pump and manometric efficiency.
Solution:
Least speed to start the pump
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