Post on 04-Apr-2018
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Irrigation Pumps
Prof. S.K. SondhiPunjab Agricultural University ,Ludhiana
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Variable Displacement pumps
Centrifugal Mixed flow Propeller Jet Air Lift
Volute Diffuser Turbine
Single stage
Multi stage
Deep well turbine
Submersible
Variable Displacement pumps
Centrifugal Mixed flow Propeller Jet Air Lift
Volute Diffuser Turbine
Single stage
Multi stage
Deep well turbine
Submersible
Classification of Pumps
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Determination of Operating
Conditions The source of water
* Surface water
* Ground water
The required pumping flow rate The total suction lift
The total dynamic head Net positive suction head available
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Determination of flow rate
Q = 27.78 AY/ RT
Q = Discharge capacity of the pump (lps)
A = area (ha) under crops
Y = depth of irrigation (cm)
R = rotation period (days)
T = duration of pumping (hrs/day)
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The total dynamic head
Ht = Hs + Hd + Hl + Hv
Ht=total dynamic head of the system (TDH)
Hs=static head (static lift + static dischargehead)
Hd=drawdownHl=friction loss head
Hv=velocity head
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Pump Performance Parameters
Capacity
Head
Power Requirements
WHP = Discharge (lps) x Total head (m)
76 BHP = Water Horse Power (WHP)
Pump efficiency X Drive efficiency
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Efficiency
Efficiency = WHP x100BHP
Net Positive Suction Head (NPSHr
)
Net positive suction head. This is the pressure apump requires for cavitation-free operation.
Specific Speed
Ns = N x Q1/2
H3/4Ns = specific speed rpm
N = pump speed rpm
Q = Discharge in m3/secH = Total Head (m)
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Working principle of centrifugal pump
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Centrifugal pump
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Net Positive Suction Head available
NPSHa = BP - SH - FL VP
BP=barometric pressure
SH=suction head or lift
FL=friction losses in the intake pipe
VP=water vapor pressure at a given temperature
The NPSHr versus Q curve can be used. The
NPSHa must be greater than NPSHr at agiven Q to avoid pump cavitation.
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Pump Characteristic curves
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Determination of the operating point for a given centrifugal pumpand water system
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Effect of Speed Change on Pump Performance
(N2/N1) x Q1 = Q2
(N2/N1)2 x H1 = H2
(N2/N1)3 x BHP1 = BHP2
N1 = Initial rpm
N2 = New rpm desired
Q =Discharge (liters per second)
H =Total Head
BHP = Brake Horsepower
C it ti i t if l
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Cavitation in centrifugal pump
The term cavitation implies a dynamic process offormation of bubbles inside the liquid, their growth
and subsequent collapse as the liquid flows
through the pump.General symptoms
*Reduction in capacity of the pump*Abnormal sound and vibrations
*Fluctuating pump motor current
Effects of cavitation
*Degraded pump
*Excessive pump vibration*Damage to pump impeller, bearings, seals
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Cavitation
Cavitation occurs when a void forms within
a pump when discharge of water is faster than intake.
Air is taken into pump
Cavitation can usually be heard- sounds
like rocks passing through pump
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Preventing cavitation
Decrease the static lift by placing the
pump near to water surface Decrease the temperature of the liquid
being pumped
Increase the diameter of suction pipe,
reduce the number of bends, fittings in the
suction pipe
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Installation of centrifugal pump
Location
Foundation
Mounting unit on foundation
Grouting unit on foundation
Alignment
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Operation of centrifugal pumps
Check the alignment of the pump
Make sure that the engine or motor will drive thepump in the direction indicated on the pumpbody.
Make sure that the gland is tightly and evenlyadjusted and the pump shaft revolved freelywhen turned by the hand.
Check the air tightness of suction pipe andleakage.
Fill the suction line and pump with water and
remove the air from pump casing. Attend the lubrication requirements
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Energy Conservation in Pumping systems
Various reasons for low efficiency of pumping1. Excessive suction lift
2. Use of sharp bends in piping system
3. Excessive height of delivery pipe from groundlevel
4. Improper selection and inferior quality of pump
5. Leakage in joints6. Lowering of undersized pipe in the suction line
7. Improper matching of RPM of pump and
motor/engine8. Use of poor quality driving belts
9. Use of poor quality reflux valve
10. Misalignment of pump and motor/engine pulley
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Example: Calculate pump capacity
Season Crop Area to be
irrigated
(ha)
Irrigation
depth per
irrigation(cm)
Rotation
period in
days
Period of
work
hours/day
Winter
(rabi)
Wheat 3 7.5 15 10
Summer
(kharif)
Maize 1 7.5 20 10
Paddy 2 5.0 2 10
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Discharge required for winter crop:
Q = 27.78(3 x 7.5)/ (15 x 10) =4.17 l/s
Discharge required for summer crop:Q = 27.78((1 x 7.5)/ (20 x 10) + (2
x 5.0)/ (2 x 10))
= 14.93 l/sTo allow for conveyance losses between the
pump and the field, increase the pumpcapacity by 20 per cent.
Therefore, the discharge rate required by
the pump = 14.93 x 1.2 = 17.92 l/s
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Determine the horse power requirements
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Determine the horse power requirements1.Discharge of the pump = 18 l/s
2. Dia. Of suction and delivery pipe = 100 mm3. Depth of water table = 3m4. Height of delivery pipe above ground surface =
1 m5. Horizontal section of delivery pipe after bend =2 m
6. Horizontal section of suction pipe betweenbend and pump = 1 m7. No. of reflux valve = 18. No. of long radius bend = 2
9. Drawdown = 3 m10. Friction loss for 100 mm GI pipe of dischargeof 18 l/s = 9m/100 m length of pipe
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Estimation of TDH
Friction losses in pipe and fittings:Total length of pipe above pumping water level =
3+3+1+9+1+2 = 19 m
The equivalent length of straight pipe for 100 mmreflux valve = 8.23.m
The equivalent length of straight pipe for 100 mm
two long radius bends = 2 x 2.13 = 4.26 mThe total friction loss in pipe and fittings =
(19+8.23+4.26)x9/100 =2.83 m
Velocity head for discharge of 18 l/s through 100
mm pipe = 0.27 m
Therefore, total dynamic head (TDH)=3+3+9+1+2.83+0.27=19.10 m
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Head calculations
Vertical turbine pump
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Motor and pump
Submersible pump
Selecting an Irrigation Pump
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Selecting an Irrigation Pump
1. Centrifugal Pump Advantages
1. High efficiency over a
range of operatingconditions
2. Easy to install.
3. Simple, economical andadaptable to manysituations.
4. Electric, engine or tractorpower can be used
5. Does not overload with
increased TDH.
Disadvantages
1. Suction lift is limited. It
needs to be within 4m ofthe water level.
2. Priming required.
3. Loss of prime candamage pump.
4. If the TDH is muchlower than design value,the motor may overload.
V ti l T bi P
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Vertical Turbine Pump
Advantages
1. Adapted for use in wells.
2. Provides high TDH and
flow rates with high
efficiency.
3. Electric or engine power
can be used.
4. Priming not needed.
5. Can be used where water
level fluctuates.
Disadvantages
1. Difficult to install, inspect
and repair
2. Higher initial cost than
centrifugal pump.
3. Repair and maintenance
is more expensive than
centrifugal pump.
Submersible Pump
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Submersible Pump
Advantages
1. Adapted for use in deep
wells
2. Priming not needed.
3. Can be used in crooked
wells
4. Easy to install.
5. Smaller diameters are
less expensive than
comparable vertical
turbine pumps
Disadvantages
1. More expensive in larger
sizes than verticalturbine pumps.
2. Only electric power can
be used.
General maintenance
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The suction lift should be periodically checked
The gland packing in the pump should be checked. The watershould drip through the packing at a rate of 15 to 30 drops perminute.
The rpm of the prime mover should be at the rated value. The alignment of the pump and motor shaft should be checked
periodically.
A record of the pump running hours, problems, servicing,maintenance and repairs should be kept in a logbook.
The inlet screen, foot valve/ reflux valve and pipe threadsshould be checked, and any corroded or damaged threads re-
cut.
The reflux valve should be checked and rubber gasket may bereplaced if worn out.
Trouble shooting in centrifugal pumps
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Trouble shooting in centrifugal pumps
1. No water delivered
Pump not properly primed
Speed too low Discharge head too high
Suction lift too high Impeller or suction pipe completely plugged
Wrong direction of rotation
Air pocket in suction line
Air leak in suction line or stuffing box
Insufficient NPSH available
2 Not enough water delivered
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2. Not enough water delivered
Air leak in suction line or stuffing box Speed too low
Discharge head higher than anticipated
Suction lift too high
Impeller or suction pipe partially plugged
Wrong direction of rotation Insufficient NPSH available
Foot valve too small Insufficient submergence of suction inlet
Wearing rings worn
3 N t h d l d
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3. Not enough pressure developed
Speed too low
Excessive amount of air or gas in liquid
Wrong direction of rotation Viscosity of liquid higher than anticipated
Wearing rings worn
Impeller diameter too small
4. Pump works for a while and then loses
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4. Pump works for a while and then loses
prime Air leak in suction line or stuffing box
Excessive amount of air or gas in liquid
Air pocket in suction line
Water seal tube clogged
Water seal ring improperly located Suction lift too high
Insufficient submergence of suction inlet
5. Pump requires excessive power
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5 u p equ es e cess e po e
Speed too high Head lower than anticipated
Specific gravity or viscosity too high
Wrong direction of rotation
Misalignment
Stuffing box too tight Rotating element tubing binding
Bent shaft Wearing rings worn
6. Stuffing box leaks excessively
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g y
Packing is worn or improperly lubricated Packing improperly installed
Incorrect type of packing
Shaft sleeve scour
Bent shaft
7. Pump noisy or vibrates
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p y
Suction lift too high Insufficient NPSH available
Impeller or suction pipe partially plugged
Misalignment
Foundation not rigid
Lack of lubrication Bearing worn
Rotating element out of balance Bent shaft
Pumping do's and don'ts
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Pumping do s and don ts
Do: site the pump as close as possible to the water
make sure suction and delivery pipes do not put a strain on
the pump casing check that all pipe connections are tight
use a strainer recommended by the pump manufacturer
anchor the pump securely so that it doesn't move duringoperation
work the pump within its limits
provide ventilation for the motor or engine keep the pump and motor connection aligned
make sure the pump is primed before starting
keep the strainer clean service the pump regularly.
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Don't:pump corrosive liquids
operate the pump without wateroperate the pump if the discharge valve is closed
operate the pump if the strainer is blocked
operate the pump if it is vibrating excessivelyinstall the suction pipes so that air can build up in them
forget to do regular maintenance.