2.
PUMPS: It is a steady-state, steady-flow machine in which mechanical
work is added to the fluid in order to transport the liquid from one point to
another point of higher pressure.
Upper
Reservoir
Suction Gauge Discharge Gauge
Lower
Reservoir
Gate Valve
Gate
Valve
3.
CLASSIFICATION OF PUMPS
1. Centrifugal: It consist essentially of an impeller arranged to rotate within
a casing so that the liquid will enter at the center or eye of the impeller and
be thrown outward by centrifugal force to the outer periphery of the impeller
and discharge into the outer case. It operates at high discharge pressure,
low head, high speed and they are not self priming.
Centrifugal
Mixed Flow
single stage
multi stage
Propeller or axial flow
Peripheral
4.
2. Rotary:It is a positive displacement pump consisting of a fixed casing containing gears, cams, screws, vanes, plungers or similar element actuated by
the rotation of the drive shaft. A rotary pump traps a quantity of liquid and
moves it along toward the discharge point. For a gear type rotary pump the
unmeshed gears at the pump provides a space for the liquid to fill as the
gears rotate. The liquid trapped between the teeth and the pump casing is
eventually released at the discharge line. It operates at low heads, low discharge and is used for pumping viscous liquids like oil.
cam
gear
screw
vane
5.
3. Reciprocating: It is a positive displacement unit wherein the pumping action
is accomplished by the forward and backward movement of a piston or a
plunger inside a cylinder usually provided with valves.
Piston
Direct Acting
single
duplex
Crank and Flywheel
Plunger
Power Driven
simplex
duplex
triplex
6.
4. Deepwell Pumps: It is used when pumping water from deep wells. The pump
is lowered into the well and operated close to water level. They are usually
motor driven with the motor being at the ground level and connected to the
pump by a long vertical line shaft.
Turbine
Ejector or centrifugal
reciprocating
Airlift
For a final choice of a pump for a particular operation the following data are needed.
Number of units required
Nature of liquid
Capacity
Suction conditions
Discharge conditions
Intermittent or continuous service
Total dynamic head
Position of pump, vertical or horizontal
Location, geographical, indoor, outdoor, elevation
Type of power drive
8.
FUNDAMENTAL EQUATIONS
1. TOTAL DYNAMIC HEAD
Ht
P2
P1
v2
2
v1
2
2g
γ
Z2
Z1
2. DISCHARGE or CAPACITY
Q = Asvs = Advd m3/sec
3. WATER POWER or FLUID POWER
WP = Q Ht KW
4. BRAKE or SHAFT POWER
BP
2πTN
60,000
KW
HL
meters
9.
5. PUMP EFFICIENCY
ηP
WP
BP
x 100%
6. MOTOR EFFICIENCY
ηm
BP
MP
x 100%
7. COMBINED PUMP-MOTOR EFFICIENCY
ηC
ηC
WP
MP
ηP ηm
x 100%
10.
8. MOTOR POWER
For Single Phase Motor
MP
EI(cosθ)
1000
KW
For 3 Phase Motor
MP
where:
3 EI(cosθ)
1000
KW
P - pressure in KPa
v - velocity, m/sec
- specific weight of liquid, KN/m3
Z - elevation, meters
g - gravitational acceleration, m/sec2
HL - total head loss, meters
E - energy, Volts
I - current, amperes
(cos ) - power factor
T - brake torque, N-m
N - no. of RPM
WP - fluid power, KW
BP - brake power, KW
MP - power input to
motor, KW
11.
PIPES and FITTINGS
Nominal Pipe Diameter: Pipe sizes are based on the approximate diameter and
are reported as nominal pipe sizes. Regardless of wall thickness, pipes of the same
nominal diameter have the same outside diameter. This permits interchange of
fittings. Pipe may be manufactured with different and various wall thickness, so
some standardization is necessary. A method of identifying pipe sizes has been
established by ANSI (American National Standard Institute). By convention, pipe
size and fittings are characterized in terms of Nominal Diameter and wall thickness.
For steel pipes, nominal diameter is approximately the same as the inside diameter
for 12" and smaller. For sizes of 14" and larger, the nominal diameter is exactly the
outside diameter.
SCHEDULE NUMBER: The wall thickness of pipe is indicated by a schedule
number, which is a function of internal pressure and allowable stress.
Schedule Number 1000P/S
where P - internal working pressure, KPa
S - allowable stress, KPa
Schedule number in use: 10,20,30, 40,60, 80, 100, 120, 140, and 160.
Schedule 40 "Standard Pipe"
Schedule 80 " Extra Strong Pipe"
12.
FITTING: The term fitting refers to a piece of pipe that can:
1. Join two pieces of pipe
ex. couplings and unions
2. Change pipeline directions
ex. elbows and tees
3. Change pipeline diameters
ex. reducers
4. Terminate a pipeline
ex. plugs and valves
5. Join two streams to form a third
ex. tees, wyes, and crosses
6. Control the flow
ex. valves
VALVES: A valve is also a fitting, but it has more important uses than simply
to connect pipe. Valves are used either to control the flow rate or to shut off
the flow of fluid.
13.
DESIGN OF A PIPING SYSTEM
The following items should be considered by the engineer when he is
developing the design of a piping system.
1. Choice of material and sizes
2. Effects of temperature level and temperature changes.
a. insulation
b. thermal expansion
c. freezing
3. Flexibility of the system for physical and thermal shocks.
4. Adequate support and anchorage
5. Alteration in the system and the service.
6. Maintenance and inspection.
7. Ease of installation
8. Auxiliary and standby pumps and lines
9. Safety
a. Design factors
b. Relief valves and flare systems
14.
HEAD LOSSES
HL = Major loss + Minor losses
Major Loss: Head loss due to friction and turbulence in pipes
Minor Losses: Minor losses includes losses due to valves and fittings,
enlargement, contraction, pipe entrance and pipe exit. Minor losses are most
easily obtained in terms of equivalent length of pipe "Le". the advantage of this
approach is that both pipe and fittings are expressed in terms of
"Equivalent Length" of pipe of the same relative roughness.
Darcy-Weisbach Equation
Considering Major Loss only
f Lv 2
hf
meters
2gD
Considering Major and Minor Losses
hf
f (L
L ) v2
e
meters
2gD
15.
Where; f - friction factor from Moody's Chart
L - length of pipe, m
Le - equivalent length in straight pipe of valves and fittings, m
v - velocity, m/sec
D - pipe inside diameter, m
g - gravitational acceleration, m/sec2
REYNOLD'S NUMBER: Reynold's Number is a non dimensional one which
combines the physical quantities which describes the flow either Laminar
or Turbulent flow. The friction loss in a pipeline is also dependent upon this
dimensionless factor
NR
where;
ρvD
vD
μ
ν
- absolute or dynamic viscosity, Pa-sec
- kinematic viscosity, m2/sec
For a Reynold's Number of less 2100 flow is said to Laminar
For a Reynold's Number of greater than 3000 the flow is Turbulent
16.
Moody’s Chart
f
D
NR
where
- absolute roughness
D - inside diameter
/D - relative roughness
17.
VALUES OF ABSOLUTE ROUGHNESS
FOR NEW PIPES
Type of Material
Drawn tubing, brass, lead, glass
centrifugally spun cement, bituminous
lining, transite
Commercial Steel, Wrought iron
Welded steel pipe
Asphalt-dipped cast iron
Galvanized iron
Cast iron, average
Wood stave
Feet
Millimeter
0.000005
0.00015
0.00015
0.0004
0.0005
0.00085
0.0006 to 0.003
0.0015
0.046
0.046
0.12
0.15
0.25
0.18 to 0.9
Concrete
0.001 to 0.01
0.3 to 3
Riveted steel
0.003 to0.03
0.9 to 9
18.
For Laminar flow:
f
64
NR
Centrifugal Pumps
1. TOTAL HEAD
Ht = nH
where:
n - number of stages
H - head per stage
2. SPECIFIC SPEED: Is the speed in RPM at which a theoretical pump
geometrically similar to the actual pump would run at its best efficiency
if proportion to deliver 1 m3/sec against a total head of 1 m. It serves as
a convenient index of the actual pump type.
19.
NS
where:
N Q
Q - flow in m3/sec for a single suction pump
H - head per stage
N - speed, RPM
NS - specific speed, RPM
3
0.0194 H
4
3. SUCTION SPECIFIC SPEED
S
N Q
3
0.0194 NPSH
4
3
NS
NPSH
S
H
4
where: NPSH - Net Positive Suction Head
20.
4. NET POSITIVE SUCTION HEAD: The amount of pressure in excess
of the vapor pressure of the liquid to prevent cavitation.
NPSH = Hp Hz - Hvp - hfs , meters
where:
Hp - absolute pressure head at liquid surface at suction, m
Hz - elevation of liquid surface at suction, above or below the pump
centerline, m
(+) if above PCL
(-) if below PCL
Hvp - vapor pressure head corresponding the temperature of the
liquid,m
hfs- friction head loss from liquid surface at suction to PCL.
5. CAVITATION: The formation of cavities of water vapor in the suction side
of the pump due to low suction pressure.
21.
CAUSES OF CAVITATION
Sharp bends.
High temperature
High velocity
Rough surface
Low atmospheric pressure
EFFECTS OF CAVITATION
Noise
Vibration
Corrosion
Decreased capacity
6. CAVITATION PARAMETER
4
δ
NPSH
NS
H
S
3
22.
7. IMPELLER DIAMETER
D
60
2gH
πN
meter
where: - peripheral velocity factor whose
value ranges from 0.95 to1.09
8. AFFINITY LAWS OR SIMILARITY LAWS FOR CENTRIFUGAL
MACHINES
a. For Geometrically similar pumps
Q ND3
Power
N3D5
H N2D2
T
N2D5
b. For pumps with Variable Speed and Constant impeller diameter
Q N
Power N3
H N2
c. For pumps at Constant Speed with Variable impeller diameter
Q D
Power D3
H D2
23.
RECIPROCATING PUMPS
Specification: Ds x Dw x L
where: Ds - diameter of steam cylinder
Dw - diameter of water cylinder
L - length of stroke
1. VOLUMETRIC EFFICIENCY
ηV
Q
VD
x 100%
where: Q - discharge , m3/sec
VD - displacement volume, m3/sec
24.
2. DISPLACEMENT VOLUME
For Single acting
2
VD
L(D W ) Nn' m 3
4(60)
sec
For Double acting without considering piston rod
2
VD
L(D W ) Nn' m 3
4(60)
sec
For Double acting considering piston rod
VD
LNn'
4(60)
2
2D W - d
2
m
3
sec
where: N - no. of strokes per minute
L - length of stroke, m
D - diameter of bore, .
d - diameter of piston rod, m
n' - no. of cylinders
n' = 1 (For Simplex)
n' = 2 (For Duplex)
n' = 3 (For Triplex)
25.
3. PERCENT SLIP
% Slip = 100 -
where: hs - enthalpy of supply steam, KJ/kg
he - enthalpy of exhaust steam, KJ/kg
ms - steam flow rate, kg/hr
WP - fluid power, KW
V
4. SLIP
Slip = VD - Q
5. THERMAL EFFICIENCY
e
3600(WP)
m s (h s
he )
x 100%
6. FORCE PRODUCED and ACTING ON THE PISTON ROD
2
Fs
D S (Ps
4
Pe )
KPa
where: Ps - supply steam pressure, KPa
Pe - exhaust steam pressure, KPa
Ds - diameter of steam cylinder, m
(Ps - Pe) - mean effective pressure
26.
7. FORCE TRANSMITTED TO THE LIQUID PISTON
Fw
e m Fs
2
Fw
(Dw) (Pd
Psu )
4
Ds
(Pd
Dw
e m (Ps
where:
em - mechanical efficiency
Psu - suction pressure of water
cylinder, KPa
Pd - discharge pressure of water
cylinder, KPa
KPa
Psu )
Pe )
8. PUMP DUTY: Work done on the water cylinder expressed in
Newton-meter per Million Joules
Pump Duty
9.81m w (H d
H su ) x 10
1000m s (h s - h e )
6
N-m
Million Joules
where: mw - water flow rate, kg/hr
Hd - discharge head of pump, m
Hsu - suction head of pump, m
27.
9. PUMP SPEED
V = 43.64(L)1/2(ft), m/min
2
VD
(D W ) Vn' m
4(60)
where: ft - temperature correction factor
L - length of stroke, m
3
sec
10. TEMPERATURE CORRECTION FACTOR
ft
= 1 For cold water
= 0.85 for 32.2 C water
= 0.71 for 65.5 C water
= 0.55 for 204.4 C water
11. For Indirect Acting pumps
N
907 f t
L
28.
Example no. 1
A mechanical engineer of an industrial plant wishes to install a pump to lift 13
L/sec of water from a sump to a tank on a tower. The water is to be delivered
into a tank 105 KPa. The tank is 18 m above the sump and the pump is 1.5 m
above the water level in the sump.The suction pipe is 100 mm in diameter, 8 m
long and will contain 2 - standard elbows and 1 - Foot valve. The discharge
pipe to the tank is 65 mm in diameter and is 120 m long and contains 5 - 90
elbows, 1 - check valve, and 1 - gate valve. Pipe material is Cast iron.
Determine the KW power required by the pump assuming a pump efficiency of
70% and motor efficiency of 80%.
Other Data
= 0.001569 Pa – sec
= 1000 kg/m3
30.
Using point 1 and 2 as reference point
P1 = 0 gage
P2 = 105 Kpa
Z1 = 0
Z2 = 18 m
HL = 0.71+45.634 = 46.34 meters
Pump efficiency = 70%
Motor efficiency = 80%
Overall Efficiency = 0.70(0.80)=0.56
31.
A centrifugal pump design for a 1800 RPM operation and a head of
61 m has a capacity of 190 L/sec with a power input of 132 KW.
What effect will a speed reduction to 1200 RPM have on the head,
capacity and power input of the pump? What will be the change in H,
Q and BP if the impeller diameter is reduced from 305 mm to 254 mm
while the speed is held constant at 1800 RPM. Neglect effects of
fluid viscosity.
Given:
N1 = 1800 RPM
N2 = 1200 RPM
H1 = 61 m
H2 =
Q1 = 190 L/sec
Q2 =
BP1 = 132 KW
BP2 =
For N1 = N2 = 1800 RPM
D1 = 305 mm ; D2 = 254 mm
32.
FROM AFFINITY LAWS OR SIMILARITY LAWS FOR
CENTRIFUGAL MACHINES
a. For Geometrically similar pumps
Q ND3
Power
N3D5
H N2D2
T
N2D5
b. For pumps with Variable Speed and Constant impeller diameter
Q N
Power N3
H N2
c. For pumps at Constant Speed with Variable impeller diameter
Q D
Power D3
H D2
33.
PREPARED BY: ENGR. YURI G. MELLIZA
XAVIER UNIVERSITY
ATENEO DECGAYAN
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