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Affinity laws
Pumping Terms
Effect of Impeller diameter change

### 1. Affinity law

Centrifugal pump is a dynamic device which generates discharge pressure with impeller rotation.

Impeller rotation is directly connected to fluid peripheral velocity and generated head.

Centrifugal pump affinity laws states relation between impeller rotation with Flow rates, Generated head,  Power consumption.

Flow rate [Q] is directly proportional to rotational speed of Impeller [N].
Impeller Diameter [D] is directly proportional to rotational speed of Impeller [D].

Q ∝ N  ;  Q ∝ D

Head [H] is directly proportional to square of impeller rotational speed [N].
Head [H] is directly proportional to square of impeller diameter [D].

H N2 ;  D2

Suction requirement is also increasing in square proportion with increasing in flow.

NPSHR ∝ N²

Power [P] is proportion to cube of impeller rotational speed [N].
Power [P] is proportion to cube of impeller diameter [D].

P N ;  D3

Example : 1

If Pump RPM is 1750 and giving 100 m3/hr discharge flow. If we double Pump RPM then how much flow will be generated

Q1 = 100 M3
Q2 = ?
N1 = RPM1 = 1750
N2 = RPM2 = 3500

Q2 = 200 m3/hr

Example : 2

Pump head is 100 meter on 1750 RPM then how much head generated on 3500 RPM?

H1 = 100 meter
H2 = ?
N1 = RPM1 = 1750
N2 = RPM2 = 3500

H2 = 400 meter

Example : 3

Pump power consumption 5kW on 1750 RPM then how much power consumption will be on 3500 RPM?
P1 = 5 kW
P2 = ?
N1 = RPM1 = 1750
N2 = RPM2 = 3500

P2 = 40 kW

#### Conclusion

When we double pump RPM then
• Head will be 4 Times
• Power consumption will be 8 Times
Pumping Terms

Pump diacharge pressure is required to transfer liquid.

But there are resistance in system called losses.

Losses in pumping system are two types.

1. Static loss or static head
2. Friction loss or Dynamic loss