HYDRAULIC MACHINES
Used to convert between hydraulic and mechanical energies.
Pumps: Convert mechanical energy (often developed from electrical source) into
hydraulic energy (position, pressure and kinetic energy).
Water turbines: Convert hydraulic energy to mechanical energy and mechanical
energy is used to drive generators that develop electricity.
Water turbines are generally designed and manufactured to each power stations
own conditions of water head, discharge, water and power demands.
Electrical energy-> MOTORS-> Mechanical Energy->PUMPS-> Hydraulic Energy
(Input)
(shaft power)
(Output)
Mechanical -> TURBINES-> Mechanical Energy->GENERATORS-> Electrical Energy
Energy (Water, Input)
(shaft power)
(Output)
Pumps are available everywhere, applications are wide reaching.
Principle: A vacuum is created in the working chamber by expelling air. The pressure
on the fluid surface in the sump will then be higher than in the working chamber of
the pump; thus fluid is lifted into the chamber by the pressure difference. The fluid
will then be pushed to the delivery pipe either by displacement or under a pressure
head.
Role of civil engineers. ….
Small electric pump
Gear pump
Positive displacement pumps
Positive displacement pumps have an expanding cavity on the suction side
and a decreasing cavity on the discharge side. Liquid flows into the pumps as
the cavity on the suction side expands and the liquid flows out of the
discharge as the cavity collapses. The volume is constant given each cycle of
operation.
Peristaltic pump
Reciprocating pump
Velocity Pumps
Rotodynamic pumps (or dynamic pumps) are a type of velocity pump in which
kinetic energy added to the fluid by increasing the flow velocity. This increase
in energy is converted to a gain in potential energy (pressure) when the velocity
is reduced prior to or as the flow exits the pump into the discharge pipe. This
conversion of kinetic energy to pressure can be explained by the First law of
thermodynamics or more specifically by Bernoulli's principle.
Axial Flow Pump
Centrifugal Pump
Key features of Screw Centrifugal Impeller are:
•Energy savings of up to 50% compared with
conventional centrifugal pumps. Same high
efficiency maintained in Hidrostal’s immersible,
submersible and end suction pumps
•Non-clog impeller suitable for pumping high
consistency media and large diameter solids
beyond the capacity of centrifugal and
recessed impeller pumps
•Easy adjustment of impeller clearance permits
continuity of original high-efficiency
performance
•Optional renewable liner to reduce
maintenance costs when pumping abrasive
media.
•Low N.P.S.H characteristics
•Available in choice of materials
Pump Efficiency
e= output/input = water power /shaft power
PumpEfficiency  ( QH ) / (TN )
Q  flowrate, capacity
H  totalhead ( statichead  losses )
T  torque  of  shaft
N  speed (rpm, rad / sec)
SKETCH
Geometrically Similar Pumps
Example: A model pump of 125 mm diameter develops 185W at a speed of 800
rpm under a head of 760 mm. A geometrically similar pump 380 mm diameter is to
operate at the same efficiency at a head of 15 m. What speed and power should be
expected?
Alterations to the Same Pump
Example 2: A pump tested at 1800rpm gives the following results: capacity 253 l/s,
head=48 m , power =141.7KW. A) Obtain the performance of this pump at 1600
rpm. B) If along with the speed the diameter of the impeller is reduced from 380
mm to 356 mm, obtain the revised pump characteristics.
Similarity Laws Again…
When the shaft horsepower supplied to a certain centrifugal pump is 25 hp, the
pump discharges 700 gpm of water while operating at 1800 rpm with a head rise of
90 ft. A) If the pump speed is reduced to 1200rpm, determine the new head rise
and shaft horsepower. Assume the efficiency remains the same. B) What is the
specific speed (Ns) for this pump?
PUMP PERFROMANCE CHARACTERISTICS
-The actual head rise is always less than the ideal head rise by an amount equal to
the head loss.
-SKETCH –ideal / maximum head rise
U 22 U 2 cot 2
Head 

Q
g
2 r2b2 g
-SKETCH – effect of losses on flow rate curve
Pump performance/characteristics curves: Actual head rise gained by fluid
through a pump is determined through experiments and is usually given in plots of
ha, efficiency, shaft speed and brake horsepower versus Q (capacity).
Head developed at zero discharge is shutoff head.
Total power applied to the shaft= Brake horsepower.
Actual pump efficiency includes hydraulic losses, mechanical efficiency (in
bearings and seals) and volumetric efficiency (due to leakage).
PUMP PERFORMANCE CURVES
Different size pumps and 1 speed
Single pump different speeds
SYSTEM HEAD CURVE- important for selection of a pump and it represents the
behavior of the piping system.
Hp  H s  h f  hm
Hs  statichead
h f  frictionloss
hm  min orlosses
For any piping system there are losses. Hp is used to calculate the power
requirements for the pump.
P   QHp / e
SKETCH
SYSTEM HEAD CURVE
For any given discharge a certain Hp must be supplied to maintain that flow. We
can construct a Hp versus Q curve for each system. This is called the system curve.
For any given centrifugal pump will have a head versus discharge curve. This is the
characteristic curve at a given pump speed. This supplied by the manufacturer.
SKETCH
As discharge increases in a pipe the head required for the flow increases but the
head produced by the pump decreases as discharge increases.
The point of intersection is….
Example 1: What will be the discharge in this water system if the pump has the
characteristics shown below.
Q m3/s: 0 0.05 0.10 0.15 0.2 0.25 0.3 0.35
Hp m:
55 57
55
52
48 40 25 10
Assume Ke=0.5 and Kb=0.35, KE =1.0
Example 1:Operating condition occurs at Q=0.27 m3/s
70
60
System Curve
40
Head (m)
H versus Q Curve
Operating Point
50
30
20
Pump Curve
10
0
0
0.05
0.1
0.15
0.2
Q (m3/s)
0.25
0.3
0.35
0.4
Q (L/s)
0
32
50
63
82
101
Example 2
Q (m3/s) Pump Curve Efficiency System Curve
0
38
0
22.0
0.032
36
54
24.4
0.05
34
64
27.8
0.063
32
68
31.2
0.082
27
70
37.6
0.101
21
67
45.7
Operating point Q = 65 l/s , H=32 m, efficiency=68%, input Power= 30KW
Head (m), Efficiency (%)
80
Efficiency
70
60
50
System Curve
40
30
Pump Curve
20
10
0
0
0.02
0.04
0.06
Q (m3/s)
0.08
0.1
0.12
EXAMPLE 3:
It is necessary to select a pump to deliver water from a source to a location 25 m higher
in elevation. A 0.25 m diameter cast iron pipeline 1000 m long will be used. At the
destination end of the pipe it is required that a pressure of 50,000 N/m2 be available.
The required flow rate is 25 l/s and the water temperature is 20 degrees Celsius. Using
the pump performance curves given below determine the optimum pump (hp) for this
situation.
EXAMPLE 3: Solution
Q (l/s)
Q (m3/hr)
H (m)
10
36
30.3
25
90
31.2
40
144
32.9
EXAMPLE 3: Solution
Q (l/s)
Q (m3/hr)
H (m)
10
36
30.3
25
90
31.2
40
144
32.9
90 m3/hr
~110 m3/hr
MULTIPLE PUMP SYSTEM
A single pump is suitable within a narrow range of head and discharge in proximity of
pump efficiency. However, in a piping system the discharge and head requirements may
vary considerably at different times. Within a certain range, these fluctuations in head
and discharge can be accommodated by adopting variable-speed motors. Pump
characteristics can be altered by suitable adjustment of the speed. When the fluctuations
are considerable or the head or capacity requirement is too high for a single pump, two or
more pumps are used in series or parallel.
It’s advantageous from both a hydraulic and economic considerations to use pumps of
identical size to match their performance characteristics. Pumps are used in series in a
system where a substantial head changes take place without appreciable difference in the
discharge (i.e. the system curve is steep). In series each pump has the same discharge.
The parallel pumps are useful for systems with considerable discharge variations with no
appreciable head change. In parallel, each pump has the same head.
PUMPS IN SERIES
The following relations apply:
H=Ha+Hb+ Hc+….
Q=Qa=Qb=Qc
η (efficiency)= (Ha+Hb+….)
(Ha/η+Hb/η+…)
P   Q( Ha  Hb  ...) / 
Where a, b , c… refer to different pumps. The composite head characteristics curve is
prepared by adding the ordinates (heads) of all pumps for the same values of discharge.
The intersection of the composite head characteristics curve and the system head
provides the operating condition.
SERIES EXAMPLE
Same Q required but increased losses due to
changes in system.
Pump from example 1 in series
System curve -1 Hp=30+127Q2
System curve -2 Hp=30+600Q2
Q
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
140
Pump1
58
57
55
52
48
40
25
10
120
Head (m)
100
80
Pump1
Pump 1+2
60
System-1
System-2
40
20
0
0
0.05
0.1
0.15
0.2
Q m3/s
0.25
0.3
0.35
0.4
Pump System- System1+2
1
2
116
30.0
30.0
114
30.3
31.5
110
31.3
36.0
104
32.9
43.5
96
35.1
54.0
80
37.9
67.5
50
41.4
84.0
20
45.6 103.5
PUMPS IN PARALLEL
For pumps in parallel, the following relations apply:
H=Ha=Hb= Hc=….
Q=Qa+Qb+Qc
η= (Qa+Qb+….)
(Qa/η+Qb/η+…)
P   H (Qa  Qb  ...) / 
Where a, b , c… refer to different pumps. The composite head characteristics curve is
prepared by adding the abscissas (discharges) of all pumps for the same values of head.
The intersection of the composite head characteristics curve and the system head
provides the operating condition.
PumpPump-1 1+2
0
0.00
0.05
0.10
0.1
0.20
0.15
0.30
0.2
0.40
0.25
0.50
0.3
0.60
0.35
0.70
PARALLEL EXAMPLE
Larger capacity required for destination but
less losses in system.
Pump from example 1 in parallel
System curve -1 Hp=30+127Q2
System curve -2 Hp=30+60Q2
Parallel
70
60
Head (m)
50
Pump-1+2
40
Pump-1
30
System-1
System-2
20
10
0
0.00
0.10
0.20
0.30
0.40
0.50
Q (m3/s)
0.60
0.70
0.80
System- SystemHead
1
2
58
30.0
30.0
57
30.3
30.2
55
31.3
30.6
52
32.9
31.4
48
35.1
32.4
40
37.9
33.8
25
41.4
35.4
10
45.6
37.4
Limit on Pump Location (Net Positive Suction Head,
NPSH)
• We have considered total head, capacity, power and efficiency
requirements.
• Condition at the inlet of the pump is critical.
• Inlet or suction system must a smooth flow of fluid to enter the
pump at sufficiently high pressure to avoid creating vapour bubbles
in the fluid.
• As pressure on fluid decreases, temperature at which vapour
bubbles form ( like boiling) also decreases.
• The suction pressure at the pump inlet must be above the pressure
of vapourization for the operating temperature of the liquid. This is
called providing Net Positive Suction Head.
• If suction pressure is allowed to decrease so vapourization occurs;
cavitation is created in the pump.
•Pump will draw liquid and vapour, bubbles will collapse under
pressure. = Noisy, vibration, wear on pump parts.
Pump location and Net Positive Suction Head, NPSH
• Pump manufacturers supply data about required net positive
suction head for proper pump operation.
• We must select pumps that ensure sufficiently high NPSH is
available.
NPSHavailable> NPSH required
NPSHavailable depends on: nature of fluid, suction piping, location
of reservoir, pressure applied to fluid in the reservoir.
NPSHa = hsp ± hs – hf – hvp (apply Bernoulli equation)
hsp = static pressure head applied to fluid (in m or ft)
hs = elevation difference from level of fluid in reservoir to pump
inlet (in m or ft).
hf = friction loss in suction piping
hvp = vapour pressure of the liquid at the pumping temperature
Pump location and Net Positive Suction Head, NPSH
Web sites: pump cavitating
http://www.youtube.com/watch?v=guHGpOzDa9A&feature=related
cavitation bubbles:
http://www.youtube.com/watch?v=3TTBs3o_09I&list=QL&playnext=5
Pump location and Net Positive Suction Head, NPSH
Pump location and Net Positive Suction Head, NPSH
Pump location and Net Positive Suction Head, NPSH
Pump location and Net Positive Suction Head, NPSH
Pump location and Net Positive Suction Head, NPSH
EXAMPLE
Pump location and Net Positive Suction Head, NPSH
Given:
Vapour pressure water at 70C= 31,200 N/m3
specific weight water at 70C = 9.59x10^3 N/m3
Kinematic viscosity water at 70C= 4.13x10^-7 m2/s
Kelbow = ƒ x30
Kvalve= ƒx340
Kentrance= 1.0
Ε=4.6x10^-5 m
Pump location and Net Positive Suction Head, NPSH
Pump location and Net Positive Suction Head, NPSH
EXAMPLE 4- elevation of pump
A centrifugal pump is to be placed above a large, open water tank, as shown below. The
pump is to pump water at a rate of 0.5 ft^3/s. At this flow rate the required NPSH is 15 ft,
as specified by the pump manufacturer. The water temperature is 80 degrees F and
atmospheric pressure is 14.7 psi. Assume that the major head loss between the tank and
the pump inlet is due to a filter at the pipe inlet having minor loss coefficient K= 20. Other
losses can be neglected. The pipe on the suction site of the pump has a diameter of 4
inches. Determine the max height (Z) that the pump can be located above the water
surface without cavitation. If you were required to place a vale in the flow path would you
put it upstream or downstream of the pump? Why?
Example Pumps in Series
A pump with a pump performance curve hp=30-200Q2 where hp
is in meters and Q is in m3/min is used to pump a fluid up a 25m
high hill. The system equation is hp= 25+100Q2.
A) Determine the flow rate expected and operating head.
B) Is this pump reasonable choice to use if the fluid is to be
pumped up a 35m high hill (hp=35+100Q2). If not use 2
pumps in series. Determine the expected flow rate.
Example Pumps in Series
Q
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Pump1
30
29.5
28
25.5
22
17.5
12
5.5
Pump 1+2 System-1 System-2
60
25.0
35.0
59
25.3
35.3
56
26.0
36.0
51
27.3
37.3
44
29.0
39.0
35
31.3
41.3
24
34.0
44.0
11
37.3
47.3