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 mn = 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

HQn

ns

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 3626014502

550002

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

homQQWheredDCQ

',

4' 22

1

965.0,,0362.1,3.22

287.01,287.0113232 V

sV

orn

21

4h

Vom

dCQD

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

32

210).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.

222UgH

ψ Pump Type0.7-1.3 Radial Impeller

0.25-0.7 Mixed-flow impeller0.1-0.4 Axial Impeller

gHnDU 2

602

2

gH

nD 260

2

11

• Choosing ψ = 1,

2) The specific diameter (δ)

The specific diameter becomes,

mDandsmU

412.0,/32.31

2

2

21

41

nDQ

DnDQ

AUQ

UC

DnY

UgH

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

CDQ

CDQb

omVom

40039.04175.0965.0

0833.0

'

111

mVm CDQ

CDQb

22222

'

smCfigurethefromkgHkC

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

nDC

UC

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

kofvaluethetakingDDDDkZ