1

Radial Pump Impeller Design (Example)

2

• Design a rotor(impeller) of a radial water pump for the following given values

Q = 300 m3/h (0.0833 m3/s)

H = 50 m

n = 1450 rpm

3

• The Specific speed for the pump is calculated from the following formula for the given values

• After finding the specific speed the shape of the impeller can be decided using the following table.

The specific speed is in the radial type pump range

3.2250

0833.014504343

H

Qnns

Shape No. Range Shape of the Impeller

10<ns<50 Radial Type

50<ns<150 Mixed Type

150<Ns<400 Axial Type

4

• The shaft Power is given as:

• The overall efficiency, ηo, for a single stage, single entry, radial pump can be read from the figure below to be ηo = 0.85.

• The pump power becomes,

o

QgHP

kWkWP 551.5185.0

5081.90833.0103

5

(Source: Centrifugal Pumps, Johann Friedrich Gülich, 2nd ed)

6

• Shaft diameter can be found using the following formula

• The torque can be calculated as it follows:

• The allowable shear stress for most of the shafts is in the range between 40 -60 N/mm2. Thus the shaft diameter becomes:

• The hub diameter, dh = 1.1 to 1.3 ds

316

ts

Td

Nmn

PPT 362

6014502

55000

2

mmdsaymmd ss 40,64.3513.32

mmdd sh 502.1

7

• The eye diameter (D1) can be calculated by assuming inlet number . The radial velocity at the inlet is given by:

• The volume flow rate at the suction end is given by:

• Calculating for the eye diameter,

• The volumetric efficiency is given by:

YCom 2

V

hom

QQWheredDCQ

',4

' 221

965.0,,0362.1,3.22

287.01,

287.01

13232

VsV

orn

21

4h

Vom

dC

QD

8

• The inlet number can be found from the following table.

Guidelines to choose ε

9

• From the table,

• Thus,

• Another option to estimate the value of inlet number is to use the formula by Pfleiderer,

• Thus, D1 becomes,

3.22,13.008.0 snfor

smsmCom /4/52.75.2

3

2210).35.1( sn

mmD 175.0173.005.0965.04

0833.04 21

10

The outer diameter D2 can be calculated using:

1) The head coefficient (ψ)

The head coefficient for different type of pumps is given below.

222U

gH

ψ Pump Type

0.7-1.3 Radial Impeller0.25-0.7 Mixed-flow impeller0.1-0.4 Axial Impeller

gHnD

U2

602

2

gH

nD

2602

11

• Choosing ψ = 1,

2) The specific diameter (δ)

The specific diameter becomes,

mD

andsmU

412.0

,/32.31

2

2

21

41

nD

Q

DnDQ

AU

Q

U

C

Dn

Y

U

gH

m322

22222

4

4

22

2/1

4/12

2/1

32

4/1

22221

41 05.142Q

YDnD

QDnY

12

• D2 becomes,

• The specific diameter is plotted in the following diagram for various specific speeds,

• From the table, δ = 6.5.

• Thus the outer diameter can be taken to be

D2 = 0.4m

4/122/05.1 QgH

D

mD 397.00833.0/5081.905.1

5.64/122

13Cordier Diagram

14

• Blade width b1

• The Blade width at the outlet b2

• C2m can be found from figure below.

mmm

CD

Q

CD

Qb

omVom

40039.04175.0965.0

0833.0

'

111

mVm CD

Q

CD

Qb

22222

'

smC

figurethefromkgHkC

m

mmm

/45.3

,11.0,2

2

222

mmmb 200199.045.34.0965.0

0833.02

15

16

• Blade angle β0

• Blade angle β2 can be estimated from the previous figure.

• Number of blades

o

omom

nD

C

U

C

75.1660/1450175.0

4tan

tantan

1

1

1

1

10

oo to 3.238.21

43.04.0tan

2

2

approachStepanoffZ ,73

2

6

7,2

sin 21

12

21

Z

kofvaluethetakingDD

DDkZ