IMPROVEMENT OF A LOCALLY MADE CENTRIFUGAL PUMP BY MODIFYING THE GEOMETRY OF THE IMPELLER

140
Indonesian Journal of Agriculture 1(2), 2008: 140-144
Agung Prabowo et al.
IMPROVEMENT OF A LOCALLY MADE CENTRIFUGAL PUMP BY
MODIFYING THE GEOMETRY OF THE IMPELLER1)
Agung Prabowoa), Gajendra Singhb), and Chaiyaphal Kaewprakaisaengkulc)
a)Indonesian Center for Agricultural Engineering Research and Development
Situgadung, Legok, Tangerang, PO Box 2, Serpong 15310
b)Asian Institute of Technology, PO Box 4, Klong Luang, Pathumthani 12120, Thailand
c)Faculty of Agricultural Engineering, Asian Institute of Technology, PO Box 4, Klong Luang, Pathumthani 12120, Thailand
ABSTRACT
curves of the pump, so they are not able to choose a
suitable pump to meet their need. Since improvements in
An Indonesian locally made centrifugal pump with a diameter of
design are required and the actual efficiency of utilization
100 mm was selected from field survey to evaluate and improve
of power resources is one of the major components in
its performance. It was tested at three different static suction lifts
farm mechanization, adequate information to the local
(1, 2, and 3 m) and at seven rotational speeds (1700, 1800,
manufacturers as well as pump users is necessary.
1900, 2000, 2100 rpm, 2200, and 2250 rpm). The original
impeller was improved to increase performance of the pump by
In a field survey, it was found that the main problems
modifying the geometry of the impeller. The improved pump was
of the original pump were related to suction side and
tested with the experimental setup same as of the original pump.
rotating parts of the pump, which resulted in reduction of
The results showed that the discharge increased from 28.4% (at
total head, discharge and efficiency. Nemdili and Hellmann
static suction of 1 m and speed of 2250 rpm) to 58.6% (at static
(1999) stated that factors that influence the efficiency of
suction lift of 3 m and speed of 1900 rpm). The efficiency increased
from 13% (at static suction lift of 1 m and speed of 2250 rpm) to
the centrifugal pump are surface roughness, internal
50.7% (at static suction lift of 3 m and speed of 1800 rpm). The
clearances, seal components and bearings, flow rate, head
total head of improved pump and original pump were not
and speed, and balancing of the axial forces of the impeller.
significantly different.
Ludwig et al. (2000) also stated that the shape of the
impeller influences the losses caused by several pump
[Keywords: Centrifugal pump, geometry impeller, efficiency]
components, such as disk friction at the back and front
shroud or the impeller and blade friction losses within the
impeller. Therefore, an original impeller was modified to
increase the performance of the pump by modifying the
INTRODUCTION
geometry of the impeller. So, the objectives of the study
were: (1) to measure the performance of the original design
There are 188,860 centrifugal pumps of various sizes being
of locally made centrifugal pump, (2) to modify the design
used for agricultural irrigation in Indonesia (Central Bureau
of impeller of the original pump to improve the
of Statistics 2000). These pumps are produced by local
performance, and (3) to measure the performance of the
manufacturers. Most of these pumps are small pump with
improved centrifugal pump at different operating
diameter of 50 mm and medium pump with diameter of 100
conditions of static suction lift compared with the original
mm. About 56.8% and 32.4% of the farmers used small
design.
and medium pumps, respectively (Prabowo 2002). All of
medium pumps were powered with diesel engine (8.5 HP)
by pulley-belt transmission.
MATERIALS AND METHODS
Some efforts to evaluate several prototypes have been
done by Indonesian Center for Agricultural Engineering
The type of impeller used in the experiment was selected
Research and Development (ICAERD), but the Indonesian
based on the results of the field survey. It, therefore,
farmers almost know nothing about the actual performance
represents the type of centrifugal pumps impeller
commonly used by Indonesian farmers. The design of the
original impeller was 176 mm outside diameter, 76 mm inlet
diameter, inlet width 37.2 mm, outlet width 37.2 mm, 6 mm
1) Article in bahasa Indonesia has been published in Jurnal Enjiniring
Pertanian Vol. 1 No. 1, 2003, p. ...-....
vane thickness, and 5 vanes.

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Improvement of a locally made centrifugal pump ...
141
The experiments were conducted at ICAERD. The pump
were calculated by using following equations (Stepanoff
tested was a locally made centrifugal pump with 100 mm
1957; Addison 1966):
outlet diameter. Impeller was semi-open type. Dimensions
of the pump were: length, 602 mm; width, 387 mm; height,
670 mm; and weight, 57.5 kg.
(π.D .n)
u
=
1
................
(1)
The testing facility was equipped with: (1) a concrete
1
60
water tank with size of 8 m length, 4 m width, and 4 m
depth; (2) a suction pipe with diameter of 100 mm and 3 m
u
=
K √ 2gH
................
(2)
1
u
length; (3) a discharge pipe with 100 mm diameter; (4) a
pressure gage and a suction gage; (5) a gate valve on the
(60.u )
D
=
2
................
(3)
discharge pipe; (6) a right-angled triangular weir; (7) a
2
(π.n)
torque-meter; (8) a dynamic strain amplifier; (9) a digital
multimeter; (10) a digital tachometer; (11) an electric motor
V
=
K √ 2gH
................
(4)
r1
m1
of 15 kW, 2920 rpm, 50 Hz; and (12) a varispeed inverter.
Preliminary tests were conducted to determine the
V
=
K √ 2gH
................
(4)
r2
m2
performance characteristics of the original pump. The pump
was tested to measure the total head, discharge, rotational
b
=
D
1
2
speed of pump shaft, and applied torque at pump drive
b
=
D
2
1
shaft.
The evaluation of the improved pump was performed
(Q’/60)
b
=
...............
(7)
similar to that of the original pump. The improved pump
2
(D .π. _ Z.S )V
ave
u
r2
.
was also tested for pumping clean water at three different
static suction lifts of 1, 2, and 3 m. The performance curve
S2
................
(8)
of the pump was evaluated to study the effect of changes
sin (β ) =
2
S
in operating conditions such as pump speed and static
u
.
suction lift.
where:
D
: inlet diameter of impeller (m)
1
D
: outlet diameter of impeller (m)
RESULTS AND DISCUSSION
2
H
: total head (m)
K
: speed constant
Testing and evaluation of the original pump showed that
u
K
: discharge constant at inlet
some deficiencies in the design of the impeller resulted
m1
K
: discharge constant at outlet
low discharge and low efficiency. The impeller was modified
m2
n
: pump rotational speed (rpm)
and fabricated to improve the pump performance.
V
: relative velocity at inlet (m/s)
Following modifications of the impeller dimensions were
r1
V
: relative velocity at outlet (m/s)
considered:
r2
b
: impeller width at inlet (m)
a. To obtain the efficiency > 60%, the outlet vane angle
1
b
: impeller width at outlet (m)
should be 20o (Addison 1966).
2
Q’
: effective discharge at a volumetric
b. Inlet vane angle should be within the range of 15o - 50o
Z
: number of vane efficiency (m3/s)
(Stepanoff 1957).
S
: thickness of vane (mm)
c. Number of impeller vanes varies from a minimum of 6
2
D
: average diameter at outer edge
for very low specific speeds to a maximum of about 12
ave
S
: vane tangential thickness (mm) of impeller (m)
for very high specific speeds (Addison 1966).
u
u
: peripheral velocity at inlet (m/s)
d. Thickness of impeller vanes may range from 4 to 8 mm
1
β
: outlet vane angle (o)
(Addison 1966).
2
u
: peripheral velocity at outlet (m/s)
e. Outer diameter of the improved impeller should be same
2
as the original one because the pump casing is not
modified.
Impeller constants of the improved impeller from
The impeller was fabricated from hot rolled steel sheet
calculation are summarized in Table 1. The comparison of
with thickness of 6 mm (for shroud and vanes) and shafting
test results of the original and the improved pump are
bar with 87.5 and 37.5 mm diameter for the impeller eye and
presented in Table 2, 3, 4, 5, and 6. The discharge, total
the impeller bosch, respectively. The impeller constants
head, power input, efficiency, and potential energy of the

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142
Agung Prabowo et al.
Table 1. Impeller constants of the improved centrifugal pump.
28.4-58.6%. Increase in discharge of the improved pump
was mainly due to change in impeller design. Since the
Impeller constant
Value
inner diameter of impeller was increased, the flow through
the impeller also increased. The peripheral velocity at inlet
Specific speed
281.50
Speed constant
1.05
and outlet increased from 9.751 to 10.37 m/second and
Discharge constant at inlet
0.18
from 20.105 to 20.79 m/second, respectively. Increase in
Discharge constant at outlet
0.133
outlet peripheral velocity tends to reduce the outlet vane
Peripheral velocity at inlet
10.37
angle. Outlet angle of the impeller also has effect on the
Peripheral velocity at outlet (m/s)
20.79
discharge. Addison (1966) found that the smaller angle,
Relative velocity at inlet (m/s)
3.56
the more quickly did the discharge increase. The outlet
Relative velocity at outlet (m/s)
2.63
Inner diameter (m)
88.09
vane angle of the improved impeller was reduced by 44.3%
Outer diameter (mm)
176
from 34.04o to 18.96o.
Inlet vane angle (o)
18.96
Table 3 shows the difference between each pair of the
Outlet vane angle (o)
2 0
total head results. For 63% of 35 pairs there was no increase
Outlet width of impeller (mm)
19.26
in total head. Comparison of total head between improved
Inlet width of impeller (mm)
38.59
Thickness of vane (mm)
6
and original pump showed no significant difference at 95%
Numbers of vane
6
confidence level. Maximum total head obtained by the
improved pump was 19.34 m, which was not significantly
different from 19.44 m of total head of the original pump.
Modification in impeller had no effect on the total head of
the improved pump. The change in the total head was due
improved pump at seven different static suction lifts were
to the change in the peripheral velocity at outlet, the relative
compared with the performance of the original pump. The
velocity at outlet, and inner diameter of impeller. Stepanoff
confidence level of statistical analysis used to compare
(1957) stated that increased peripheral velocity at outlet
the performance of the each two types of pumps at static
and the relative velocity at outlet could improve the total

suction lift was 95%.
head. In this experiment, increasing these velocities had
.
Table 2 presents the comparison between discharge of
no significant effect on the total head of the improved
the improved pump and the original pump. Comparison
pump. The experimental measurements showed that the
between each pair of the results show improvement in
total head of the improved pump was reduced as the inner
discharge of the improved pump. The improvement of
diameter was increased from 36.60 to 88.09 mm.
discharge varied from 0.326 m3/minute for 1 m static suction
The improved pump with a six-vane impeller showed
lifts at 2100 rpm to 0.496 m3/minute for 3 m static suction lift
significant increase in the power input when compared
at 1900 rpm. At 95% confidence level, the difference between
with the original pump with a five-vane impeller. Table 4
each pair of the results indicated that there were significant
presents the differences between each pair of the power
differences in the discharge. Discharge of the improved
input results. All of the differences denote increase in power
pump was higher than that of the original pump by about
input of the improved pump. The power input of the
Table 2. Comparison of discharge of improved and original centrifugal pump.
Static
Discharge at the following speeds (m3/min)

Type of pump
suction lift
1700 rpm
1800 rpm
1900 rpm
2000 rpm
2100 rpm
2200 rpm
2250 rpm
(m)
1
Original pump
0.929
0.972
1.046
1.092
1.124
1.172
1.188
Improved
pump
1.359
1.395
1.413
1.432
1.450
1.506
1.525
Increase*
0.430
0.423
0.367
0.340
0.326
0.334
0.337
2
Original pump
0.915
0.929
0.943
0.986
1.046
1.077
1.092
Improved
pump
1.289
1.342
1.377
1.395
1.413
1.469
1.487
Increase*
0.374
0.413
0.434
0.409
0.367
0.392
0.395
3
Original pump
0.793
0.833
0.846
0.887
0.929
0.986
1.001
Improved
pump
1.255
1.307
1.342
1.359
1.377
1.413
1.432
Increase*
0.462
0.474
0.496
0.472
0.448
0.427
0.431
*Increase in dicharge of the improved impeller over the original impeller statistically significant at 95% level.

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Improvement of a locally made centrifugal pump ...
143
Table 3. Comparison of total head of improved and original centrifugal pump.
Static
Type of pump
Total head at the following speeds (m)

suction lift
1700 rpm
1800 rpm
1900 rpm
2000 rpm
2100 rpm
2200 rpm
2250 rpm
(m)
1
Original pump
10.04
11.34
12.74
13.94
15.64
17.34
18.74
Improved
pump
10.14
10.94
12.54
13.64
16.84
17.34
17.74
Differences
0.10
-0.40*
-0.20*
-0.30*
1.20
0.00*
-1.00*
2
Original pump
9.94
11.14
13.24
14.94
16.04
17.54
18.94
Improved
pump
10.44
11.64
12.94
14.74
17.44
17.74
18.74
Differences
0.50
0.50
-0.30*
-0.20*
1.40
0.20
-0.20*
3
Original pump
11.14
12.04
13.84
15.24
16.84
17.94
19.44
Improved
pump
10.94
12.04
13.74
15.24
17.84
18.84
19.34
Differences
-0.20*
0.00*
-0.10*
0.00*
1.00
0.90
-0.10*
*Differences in total head are not significant differences at 95% level.
Table 4. Comparison of power input of improved and original centrifugal pump.
Static
Type of pump
Power input at te following speeds (kW)

Suction lift
1700 rpm
1800 rpm
1900 rpm
2000 rpm
2100 rpm
2200 rpm
2250 rpm
(m)
1
Original pump
3.27
3.74
4.40
4.96
5.44
6.12
6.46
Improved
pump
3.61
3.98
4.67
5.06
6.30
6.72
6.94
Increase*
0.34
0.24
0.27
0.10
0.86
0.60
0.48
2
Original pump
3.45
3.88
4.53
5.08
5.59
6.25
6.68
Improved
pump
3.65
4.18
4.76
5.46
6.46
6.81
7.19
Increase*
0.20
0.30
0.23
0.38
0.87
0.56
0.51
3
Original pump
3.62
4.13
4.87
5.16
5.85
6.59
6.91
Improved
pump
3.80
4.30
5.00
5.60
6.50
7.01
7.25
Increase*
0.18
0.17
0.13
0.44
0.65
0.42
0.34
*Increase in power input of improved impeller statistically significant at 95% level.
Table 5. Comparison of efficiency of improved and original centrifugal pump.
Static
Type of pump
Efficiency at the following speeds (%)

suction lift
1700 rpm
1800 rpm
1900 rpm
2000 rpm
2100 rpm
2200 rpm
2250 rpm
(m)
1
Original pump
46.5
48.0
49.4
50.0
52.7
54.2
56.2
Improved
pump
62.2
62.5
62.6
63.0
63.1
63.4
63.5
Increase*
15.7
14.5
13.2
12.9
10.5
9.2
7.3
2
Original pump
42.9
43.5
44.9
47.3
48.9
49.3
50.5
Improved
pump
60.1
60.9
61.0
61.4
62.1
62.4
63.2
Increase*
17.2
17.4
16.1
14.0
13.1
13.1
12.7
3
Original pump
39.8
39.6
41.2
42.4
43.3
43.8
45.9
Improved
pump
58.9
59.6
60.0
60.2
61.6
61.9
62.3
Increase*
19.2
20.0
18.8
17.8
18.3
18.1
16.4
*Increase in efficiency statistically significant at 95% level.

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144
Agung Prabowo et al.
Table 6. Comparison of potential energy of improved and original centrifugal pump.
Static
Type of pump
Potential energy at the following speeds (kJ/m3)

Suction lift
1700 rpm
1800 rpm
1900 rpm
2000 rpm
2100 rpm
2200 rpm
2250 rpm
1
Original pump
211.2
230.9
252.4
272.5
290.4
313.3
326.3
Improved
pump
159.4
171.2
198.3
212.0
260.7
267.7
273.0
Increase*
51.8
59.7
54.1
60.5
29.7
45.6
53.3
2
Original pump
226.2
250.6
288.2
309.1
320.7
348.2
367.0
Improved
pump
169.9
186.9
207.4
234.8
274.3
278.1
290.1
Increase*
56.3
63.7
80.8
74.3
46.4
70.1
76.9
3
Original pump
273.9
297.5
345.4
349.0
377.8
401.0
414.2
Improved
pump
181.7
197.4
223.5
247.2
283.2
297.7
303.8
Increase*
92.2
100.1
121.9
101.8
94.6
103.3
110.4
*Increase in potential energy statistically significant at 95% level.
improved pump increased by 2-15.8% as compared to the
CONCLUSION
original pump due to increase in discharge and also in
weight of the improved impeller. The total weight of
The percentage improvement of the discharge ranges from
improved impeller was 2.84 kg or about 33% more than the
a minimum of 28.4% at static suction lift of 1 m and speed
weight of the original impeller. It was fabricated from hot
of 2250 rpm to a maximum of 58.6% at static suction lift of
rolled steel sheet and shafting bar. The original impeller
3 m and speed of 1900 rpm. The percentage improvement
was fabricated from cast iron having 2.09 kg weight.
of the efficiency ranges from 13% at static suction lift of 1
Increase in the weight improved the torque of the pump
m and speed of 2250 rpm to 50.7% at static suction lift of 3
shaft, which resulted in higher power requirement of the
m and speed of 1800 rpm. The percentage improvement of
improved pump. The weight of the improved impeller could
the power input ranges from 2% at static suction lift of 1 m
be reduced by decreasing the vane thickness and changing
and speed of 2000 rpm to 15.8% at static suction lift of 1 m
material to cast iron.
and speed of 2100 rpm.
Table 5 shows significant improvement in efficiency of
The total head of the improved and the original pump
the improved pump and over the original pump. Efficiency
were not significantly different. Modification of the impeller
of the improved pump increased by about 13-50.7%
was not effective to improve the total head. The percentage
compared to the original pump at 1-3 m of static suction
of energy requirement of the improved pump reduced from
lift. The improved pump acheived maximum efficiency of
10.2% at static suction lift of 1 m and speed of 2100 rpm to
63.5 % at the speed of 2250 rpm and static suction lift of 1
35.3% at static suction lift of 3 m and speed of 1900 rpm.
m, whereas, the original pump achieved 56.2 % maximum
efficiency of at the same speed and static suction lift.
Improvement in the pump efficiency was due to significant
REFERENCES
increase in discharge of the pump.
Addison. 1966. Pumps. Mc.Graw-Hill Book Company, England, UK.
Table 6 presents the comparison of potential energy of
Central Bureau of Statistics. 2000. Statistical Yearbook of Indonesia,
the improved pump with the original pump. The potential
Central Bureau of Statistics, Jakarta, Indonesia.
energy is the energy requirement for pumping a unit volume
Ludwig, G., S. Meschkat, and B. Stoffel. 2000. Design Factors
Affecting Pump Efficiency. Darmstadt University of
of water. The potential energy is used to calculate the cost
Technology. Magdalenenstrabe 4, D-64289 Darmstadt,
of pumping water while selecting a pump. Potential energy
Germany.
of improved pump increased proportionally with increase
Nemdili, A. and D.H. Hellmann. 1999. The requirements to
successful centrifugal pump application for desalination and
in discharge and decreased proportionally with increase
power plant processes. The Conference on Desalination and
in efficiency. The energy requirement of the improved pump
The environment, Las Palmas, Gran Canaria, 9-12 November
reduced from 10.2% to 35.3% as compared with the energy
1999. European Desalination Society and The International
Water Association.
requirement of the original pump. At a static suction lift of
Prabowo, A. 2002. Evaluation and Improvement of Locally Made
1 m, the improved pump has the lowest potential energy
Centrifugal Pump Commonly Used In Indonesia. Thesis. No.
AE–02–1. Asian Institute of Technology, Bangkok, Thailand.
but the efficiency was highest. The potential energy at the
Stepanoff, A.J. 1957. Centrifugal and Axial Flow Pumps. John
the maximum efficiency was 273 kJ/m3.
Wiley and Sons. Inc., New York, USA.

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