Sufficient quantity of water is necessary for efficient farming. Pump is the most effective means for lifting water from open wells, tube wells, ponds, streams and rivers. The type of pump required for the purpose depends upon the suction lift and delivery head.
Commonly used pumps for agricultural purpose are as follows: 1. Centrifugal Pump 2. Vertical Turbine Pump 3. Submersible Pump 4. Propeller Pump 5. Jet Pump 6. Reciprocating Pump.
1. Centrifugal Pump:
Centrifugal pump is a rotary machine in which an impeller rotates inside a casing, draws in the liquid at its centre (eye) and throws out the liquid through an opening at the side of the casing- due to centrifugal force.
Advantages:
This pump is very popular due to the following reasons:
i. Lower initial cost
ii. Greater flexibility in application
iii. Wide working range in size and capacity
iv. Simplicity in construction
v. Constant steady discharge
vi. Easy in operation, maintenance and repair
Working Principle:
The pump consists of two basic components:
i. Impeller and
ii. Casing
The impeller is rotated at high speed by an electric motor or an engine. As soon as the impeller starts rotating, the blades cause the water to rotate with the impeller and impart high velocity to the water. Hence water in the impelled (filled up by priming in the beginning) is thrown out the impeller (eye). The static water in the well is at the atmospheric pressure, so the water rushes into suction pipe due to difference of pressure.
In this way, continuous flow of water is maintained in the pump. The centrifugal pump is so called because the pressure increases within the casing due to centrifugal forces. The pump will not work until the casing and the suction pipe are full of water by priming.
Priming:
It is the process of removing air from pump casing and suction pipe by filling water in the suction pipe. The pump will not work if there is any air left in the suction pipe.
Components and Accessories of a Pumping Unit:
The following are the important components and accessories of a pumping unit:
i. Impeller
ii. Casing
iii. Strainer with Foot Valve
iv. Stuffing box
v. Delivery pipe
vi. Delivery valve and
vii. Bearings
i. Impeller:
It is a wheel or a disc, mounted on the drive shaft and provided with a number of curved vanes or blades. The impeller is fitted on a shaft with the help of a suitable bearing. It is rotated at high speed with the help of a motor or an I.C. engine. Due to high velocity, water is thrown away from its centre towards casing outlet.
Type of Impeller:
Impellers are of three types:
(a) Open Impeller
(b) Semi-Open Impeller, and
(c) Closed Impeller
(a) Open Impeller:
This type of impeller is not provided with any side wall or shroud. Such impellers are used where water is mixed with sand, pebbles, clay and other solid materials. It is generally made of forged steel and it has a short life.
(b) Semi-Open Impeller:
This type of impeller is provided with a side wall or shrouds oil one side only. This impeller is used for viscous liquid such as sewage water, paper pulp, sugar and molasses etc.
(c) Closed Impeller:
This type of impeller is provided with side walls or shrouds on both sides of the vanes. This is suitable for handling non-viscous liquids such as ordinary water, hot water and acids etc.
ii. Casing:
It is a spiral shaped cover having gradually increasing cross sectional area towards discharge end. The casing receives water from the impeller and discharges it to the delivery pipe. It is generally made of cast iron.
The function of the casing is:
(a) To collect water from the periphery of the impeller.
(b) To transmit water to the delivery pipe at constant velocity.
(c) To eliminate the loss of head by having its spiral (volute) shape and consequently increasing the pump efficiency.
Suction Pipe:
It is a suitable pipe used for lifting water from the well or stream. The pipe is laid in such a way that it rises all its way to the pump upwards. It is fitted with suitable foot valve with strainer.
iii. Strainer with Foot Valve:
It is a non-return or one way type valve, opening upwards. The water will pass through the valve upwards and it will not allow the water to move downwards. It is fitted at the foot (bottom) of the suction pipe which remains submerged in water. It retains water in the pump and suction pipe. A suitable strainer is provided at the bottom of the valve to prevent floating bodies like leaves, wooden pieces etc. from entering into the suction pipe.
iv. Stuffing Box:
It is a portion of the casing through which the pump shaft extends and in which the packing and gland or a mechanical seal is placed to prevent leakage.
v. Delivery Pipe:
Delivery pipe is a pipe used to deliver water from the pump to the desired place.
vi. Delivery Valve:
Delivery valve is a regulating valve on the delivery side of the pump. It is a sluice type of valve which remains closed at the time of starting the pump.
vii. Bearing:
Bearing is used to keep the shaft of the pump in correct position. The bearing which gives radial position of the shaft is known as Line bearing and the bearing which gives axial position of the shaft is known as thrust bearing.
Accessories for Electric Motor Pump Set:
The important accessories used in the electrical pumping set using three phase motor are:
1. A.C. Motor Starter
2. Energy meter
3. Voltmeter
4. Ammeter
5. Indicator lamps
6. Main switch
1. A.C. Motor Starter:
If an A.C. motor is started at full line voltage, it will draw current about four times more than its normal running current. This may damage the motor and cause line disturbance. So it is necessary to use a starter to reduce the starting current in the line. Direct on line or Push button starters are commonly used for motors up to 5 hp, star delta starters are used for motors above 5 hp.
2. Energy Meter:
It indicates the amount of energy in kilowatt hours, consumed by the motor.
3. Voltmeter:
It indicates the line voltage of electrical connection.
4. Ammeter:
It indicates the amount of the current- passing in the circuit.
5. Indicator Lamps:
It shows whether all the three phases are live.
6. Main Switch:
The main switch connects the motor to the supply line.
Operating Instruction for Centrifugal Pump:
Starting:
1. Before starting the pumps, ensure that:
(a) Stuffing box is fully packed and uniformly tightened
(b) The pump shaft moves freely in its position
(c) Regulating valve on the delivery side is fully closed
(d) Suction valve is fully opened.
2. Open the priming cock as well as air-vent on the pump casing and pour water into the priming funnel. Continue pouring water until water flows out uniformly from the air-vent free from air bubbles.
3. Start the pump set and open the delivery valve for discharge of water.
Running:
1. When the pump set is running uniformly, feel the glands and bearings of the pump to see that they are not running hot.
2. See that the pump is running smooth and free from vibration.
3. See that water level in the well is within the reach of suction pipe.
4. Do not attempt to stop the leakage from the gland by excessive tightening the gland nuts because slight visible leakage from stuffing box is a good sign.
5. If the motor is overheated or giving some smoke or noise, stop the motor at once and check the voltage in all the three phases. See wire connections are alright and no fault lies in starter, main switch and terminal box.
6. Give some rest to the motor at least for half an hour for every four hours of continuous running.
Stopping:
For stopping the pump set:
i. Delivery valve should first be closed.
ii. Vacuum gauge cock (if any) on the suction side should be closed.
iii. The power unit should be shut down.
iv. Supply of cooling water (if any) should be stopped.
2. Vertical Turbine Pump:
It is a vertical axis pump fitted with rotating impellers and stationary bowls having suitable guide vanes. There is a vertical column pipe containing a vertical shaft for transmitting power to the impeller. There is a motor or an engine (prime mover) on the ground surface to rotate the vertical shaft.
Parts:
A typical vertical turbine pump consists of three assemblies:
1. Head assembly
2. Column assembly, and
3. Bowl assembly
1. Head Assembly:
The head assembly consists of the main base from which column assembly pump shaft and bowl assembly is suspended. It also contains driving unit and delivery unit of the pump.
2. Column Assembly:
The column assembly connects the bowl assembly to head assembly. This assembly contains column pipe and main shaft.
3. Bowl Assembly:
This unit consists of rotating impeller which is housed in stationary bowls having guide vanes.
Important Components of Vertical Turbine Pump Set:
The following are the important components of vertical turbine pump set:
1. Electric Motor or Engine:
Suitable electric motor or engine is installed on the ground surface for transmitting power.
2. Head Shaft:
It is an inner shaft passing through the driver hollow shaft and connecting the line shaft.
3. Column Pipe:
It is the rising main through which the liquid goes up.
4. Line Shaft:
It is a shaft between impeller shaft and head shaft
5. Impeller Shaft:
It is a shaft on which a number of impellers are mounted. This shaft is coupled to the line shaft. Usually the shaft is made of steel.
6. Impeller:
It is a rotating unit which receives liquid and throws it to the bowl passage. It may be enclosed or semi-enclosed type impeller. It may be made of cast iron or bronze depending upon the type of the pump.
7. Bowl:
It guides the flow, received from one impeller to the next impeller above. It houses the impeller and ball bearing. It is usually made of cast iron.
8. Suction Case:
It guides the flow into the eyes of the lowest impeller and carries the suction case bearing of the impeller-shaft.
9. Suction Pipe:
It helps to guide the flow to suction case and provides a safety measure in case of draw down level going below the lowest impeller.
10. Suction Strainer:
It prevents entry of large foreign matter.
Types of Lubrication:
Turbine pumps are of two types from lubrication point of view:
1. Water Lubricated Pump
2. Oil Lubricated Pump
1. Water Lubricated V.T. Pumps:
The pumps which are lubricated by water only are called water lubricated pump. No oil is necessary for such pumps. This pump is installed where water for domestic use is pumped out because domestic water should be free from oil etc.
Such pumps are provided with rubber bearings which are held in position by a ring, threaded inside the column. It is lubricated by water being pumped, thus eliminating a separate lubrication system.
2. Oil Lubricated V.T. Pumps:
The pumps which are lubricated by oil are called oil lubricated pumps. It is used in the wells producing fine sand or clay. A heavy steel tube protects the shaft and bearings from corrosion and carries the lubricating oil to each bearing, the full length of the shaft.
Working Arrangement of Vertical Turbine Pumps:
1. Vertical shaft is rotated by a motor or an engine, installed at the ground surface.
2. A casing (bowl) houses the impeller and guide vanes. When several bowls are connected in series to obtain the head, the pump is called multistage pump. Two or more stages are placed in series for deep wells.
3. As the bowls are always submerged in water, priming of the pump is not necessary.
4. The pump has a screen at the bottom to prevent coarse sand and gravel from entering into the pipe.
5. The drive shaft of the pump is fitted in the centre of the column pipe.
6. Shaft is usually made of stainless steel in the length of 3 metres only, connected by thread couplings. They are fitted with non-corrosive metal sleeves at the point of bearing contact.
7. The pump column is made of pipe section of three metres length.
8. Bearing retainers are located in each bearing. Couplings are anchored between column pipe ends.
9. The bowls are so designed that water thrown out by the rotating impellers are carried upwards through guide vanes into the centre of the impeller of the second stage.
Trouble Shooting in Vertical Turbine Pump:
Some of the causes and remedies are:
Trouble – 1- Pump Does Not Start:
1. Cause – Defective motor or its connection. Remedy – Check & repair
2. Cause – Pump not in alignment. Remedy – Check & align
3. Cause – Impellers clogged. Remedy – Check & clean
4. Cause – Impellers not well fitted. Remedy – Check & readjust
Trouble – 2 – Pump Does Not Deliver Water after Start:
1. Cause – Pump bowl out of order. Remedy – Check & readjust
2. Cause – Incorrect rotation of driver. Remedy – Check & rectify
3. Cause – Pumping head is too high. Remedy – Check & adjust
4. Cause – Pump speed too low. Remedy – Check & increase
5. Cause – Suction file clogged. Remedy – Check & clean
6. Cause – Leakage in column pipe. Remedy – Check & arrange
7. Cause – Loose impeller or broken shaft or broken bowl assembly. Remedy – Check & rectify
Trouble-3 – Not Adequate Discharge:
1. Cause – Head too high. Remedy – Check & reduce
2. Cause – Speed too low. Remedy – Check & increase
3. Cause – Air leakage in suction pipe. Remedy – Check & rectify
4. Cause – Leakage in column pipe. Remedy – Check & rectify
5. Cause – Incorrect impeller adjustment. Remedy – Check & rectify
3. Submersible Pump:
A turbine type of pump when close coupled to a suitable submersible electric motor is called a submersible pump. The pump and motor remain fully submerged in water. In such pumps there is no vertical shaft in column pipe.
Components:
The pump unit has the following important components:
1. Pump
2. Motor assembly
3. Discharge column pipe
4. Head assembly and
5. Water proof cable
Electric Motor:
The submersible electric motor has the same diameter as the pump bowl but it is much longer than an ordinary motor. A suitable seal above the armature prevents entrance of water at the point where drive shaft water at the point where drive shaft passes through the case of the impellers. Water proof electric cable joins the starting box on the ground and electric motor. The cable is placed outside the delivery pipe.
Installation, Operation and Maintenance:
1. The motor pump assembly is lowered first into well adding pipe lengths as required.
2. The cable is taped to the column pipe at every 3 metres length.
3. The pump and delivery pipe are supported by a pipe clamp at the top of the well.
4. No pump house is required because pump and motor assembly remain inside the well.
5. The control board consisting of switch. The pump is started with sluice valve closed or slightly opened.
Advantages:
1. It is very easy in installation.
2. It can be used in very deep well where long shaft cannot be installed.
3. It can be used in crooked wells where ‘vertical turbine pumps’ cannot be used.
4. Motor and pump do not need much attention. Hence operation and maintenance is very easy.
5. It can be used even when the land is flooded with water.
Disadvantages:
If the motor or the pump goes out of order the entire unit is required to be lifted up and repair or replacement becomes very costly.
Trouble Shooting in Submersible Pump:
Some of the causes and remedies are:
Trouble- 1 – Pump Fails to Start:
1. Cause – Fuses blow. Remedy – Fit the new fuse
2. Cause – Overload trip flies short circuit. Remedy – Check and rectify the circuit
3. Cause – Heavy load on pumps. Remedy – Reduce the load
Trouble – 2 Discharge of Water not Sufficient:
1. Cause – Motor running in reverse direction. Remedy – Check & rectify
2. Cause – Pump is operating against a head greater than intended. Remedy – Check & reduce
3. Cause – Pump suction is blocked by foreign matter. Remedy – Check & clean
4. Cause – Pump is air locked. Remedy – Check & rectify
5. Cause – Reflux valve jammed. Remedy – Check & rectify
6. Cause – Voltage lower than required. Remedy – Check the power supply
Trouble – 3 Discharge is Below Normal:
1. Cause – Fault in power supply. Remedy – Check & rectify
2. Cause – Friction in pump or motor. Remedy – Check & rectify
3. Cause – Leak in riser pipe. Remedy – Check & rectify
4. Cause – Pump is worn out. Remedy – Check & rectify
4. Propeller Pump:
A pump working on the principle of propeller is called propeller pump. Propeller pumps are suitable where high discharge of water is needed at low heads.
The important components of the pumps are:
1. Head assembly
2. Impeller and
3. Discharge column pipe
Pump shaft extends from the head assembly down the centre of the column pipe to drive the impeller.
Construction and Operation:
Construction and operation of these pumps are such that the flow of water is parallel to the axis of the drive shaft rather than radial. The principle is similar to that of a boat propeller, except that the impeller is enclosed in housing. Such pumps are suitable to handle large volume of water at low heads and at speeds much higher than those of ordinary centrifugal pumps. Propeller pumps are usually used for 1 to 2.5 metres head only.
The propeller operates in a casing which is cylindrical in shape. The water is moved upwards by the impeller blades. Velocity is imparted by every blade of the impeller in the direction of the shaft. The number of blade is usually 3 to 5. The propellers are usually made of bronze and are generally cast in one piece. The discharge column, discharge head and pump drive of the propeller pumps are very much similar to the vertical turbine pump.
5. Jet Pump:
It is a pump which consists of a centrifugal pump and a jet mechanism (or ejector). The centrifugal pump operates at the ground surface and jet is placed in the well below the water surface. The centrifugal pump provides the driving head and capacity for the jet to be operated in the well.
Components:
The main components of a jet pump are:
1. Nozzle and
2. Venturi
The nozzle is so shaped that it abruptly reduces the area through which the flow must pass, thus increasing the flow. A low pressure area around the venturi is created which draws more water from the well.
The impeller of the centrifugal pump creates vacuum in the pipe and draws the flow through suction pipe. The control valve is set to maintain the necessary pressure in the pipe line.
Advantages and Disadvantages:
1. Jet pump is considered very suitable for low capacity deep well pumping.
2. It can be used for high suction lift where ordinary centrifugal pump cannot be used. The suction lift varies from 12 to 18 metres.
3. All moving parts are working on the ground surface.
4. It is simple in construction and easy in maintenance.
5. Efficiency of such pump is low.
6. Reciprocating Pump:
Reciprocating pump consists of a cylinder and a piston (or a plunger). The piston moves in the air tight cylinder. Water is discharged due to reciprocating action of the piston.
Working Principle:
In reciprocating pump, a piston slides up down inside an air tight cylinder with the help of a connecting rod or a pump rod. Usually piston is fitted with cup shaped leather bucket.
There are at least two valves:
1. Inlet valve
2. Discharge valve
Inlet valve is placed at the bottom of the cylinder and the discharge valve is placed in the piston (or plunger). When the piston goes up, partial vacuum is created inside the cylinder and water forces into the cylinder through the inlet valve.
When the piston goes down, water comes out through the discharge valve of the piston. This type of pump is called positive displacement pump, because the pump discharges a volume of water equal to the volume displaced by the piston. These pumps are useful for little discharge of water.
Reciprocating pump may be:
(a) Single acting
(b) Double acting
Single acting pump has only one discharge stroke in every two strokes of the piston. In a double action pump, water is delivered at every stroke.
Comparative Study of Different Pumps:
1. Centrifugal Pump:
Pumping depth – 3 – 4.6m
Advantages:
(i) Smooth even flow.
(ii) It may pump water containing sand or silt.
(iii) Low starting torque.
(iv) Reliable and good service
(v) Free from shocks and vibrations.
Disadvantages:
(i) Looses primed water easily
(ii) Special care to maintain designed head and speed.
2. Vertical Turbine Pump:
Pumping depth – more than 7.5m
Advantages:
(i) Smooth even flow.
(ii) Low starting torque
(iii) Reliable and good service.
(iv) Free from shocks and vibrations.
Disadvantages:
(i) Special care needed to maintain designed head and speed.
(ii) Requires a sufficiently straight well. Requires special care for making the shaft vertical in the well and alignment is difficult.
(iii) Not suitable for water containing sand or silt.
(vi) Liable to abrasion from sand.
3. Submersible Pump:
Pumping depth – more than 7.5m
Advantages:
(i) Short pump shaft to motor.
(ii) Plumbness and alignment of well not difficult.
(iii) Less maintenance problem.
(iv) Lower installation cost.
(v) Lower noise.
Disadvantages:
Repair of unit requires complete removal from well Repair or replacement of motor and pump is costly.
4. Propeller Pump:
Pumping depth – 1 – 2.5m
Advantage:
High discharge at low heads.
Disadvantages:
Its use is very limited due to less pumping depth.
5. Jet Pump:
Pumping depth – 12 – 18m
Advantages:
(i) Suitable for low capacity deep well pumping.
(ii) It can be used for high suction lift where ordinary centrifugal pump cannot be used.
(iii) Simple in construction and easy in maintenance.
Disadvantage:
Efficiency is low
6. Reciprocating Pump:
Pumping depth – up to 45m
Advantages:
(i) Useful for home water supply.
(ii) It is positive dis placement pump.
(iii) Develops high head at low capacity.
Disadvantages:
(i) Capacity is low.
(ii) Not suitable for irrigation.
Different Types of Drive in Pumping Sets:
The following types of drive are used in different pumping sets:
1. Direct drive
2. Belt drive
3. Right angle gear drive
4. Power take-off drive
1. Direct Drive:
When speed of drive and the pump are same, direct drive is used through flexible coupling or it may be close coupled. It is the most efficient drive.
2. Belt Drive:
It may be V-belt drive or Flat belt drive. V-belt drive is more efficient than Flat belt drive.
3. Right Angle Gear Drive:
In this drive, a gear head containing a number of gears are used to operate the pump at suitable speed with the help of universal joint or flexible joint.
4. Power-Take Off Drive:
In this drive, the power take-off shaft of a tractor is utilised which has a speed of 540 rev/min. With suitable speed increase arrangement, pto drive is used for operating pumping sets.
Calculation of Pumping:
Cost calculation of pumping includes:
1. Fixed Cost
2. Operating Cost
1. Fixed Cost:
It includes:
(а) Interest on the capital cost
(b) Depreciation of the machine.
2. Operating Cost:
It includes:
(а) Fuel consumption of I.C. engine or electrical energy consumption if electric motor is used.
(b) Lubricating oil or grease.
(c) Spare parts and repair of engine and pump
(d) Wage of operator.
Water Horse Power (WHP):
It is the horsepower which is required to pump the water if the pump and drive (motor) are 100% efficient.
WHP = discharge (litres/sec) x total head (m)/75
= discharge (litres/min) x total head (m)/4500
= discharge (cubic metres/sec) total head (m)/273
Shaft Horse Power (SHP):
It is the power available at the pump shaft. It is the ratio of water horse power and pump efficiency.
SHP = WHP/Motor Efficiency
Brake Horse Power:
It is the power supplied by motor or engine.
When drive efficiency is 100%
BHP = WHP/Pump Efficiency = SHP
When drive efficiency is not 100%
BHP = WHP/Pump Efficiency x Drive Efficiency
Input HP = BHP/Motor Efficiency
Input to Motor (HP) = WHP/Pump Ƞ x Drive Ƞ x Motor Ƞ
Input to Motor (kW) = BHP/0.746 x Motor Efficiency