Water lifting devices are used both in irrigation and drainage. When the sources of irrigation is at a higher level than the field to be irrigated (e.g. reservoirs) water flows by gravity to the field to be irrigated.
This is known as flow irrigation. When the source is at a lower level than the area to be irrigated, the water has to be lifted for irrigation and this method of irrigation is referred to as lift irrigation.
Tubewells and pumping from rivers or streams are examples of lift irrigation. In addition to being used in lift irrigation, water lifting devices are also used in drainage. In situations where free gravity flow is not possible water lifts are used to dispose off surface or subsurface drainage water.
Water lifting devices may be classified into four groups based on the kind of power commonly used for their operation.
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These are:
1. Devices operated by human power,
2. Devices operated by animal power,
3. Devices operated by mechanical power, and
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4. Devices operated by other sources of power like hydro-power, wind power and solar energy.
Human Powered Devices:
The scoop is one of the oldest devices. This is operated by a single person to give some mechanical advantage the scoop is sometimes suspended to a tripod. The swing basket is operated by two persons facing each other. Each person holds two of the ropes and swing the basket, alternatively filling it from the source and emptying it into the delivery channel. Swing basket can be used upto a lift of 1 m.
The counterpoise lift is another human powered water lifting device. It operates on the lever principle. Its output is more than the water lifting devices. The device consists of a long wooden pole which is pivoted approximately at the centre by a cross bar.
Tree trunks of suitable shapes are used for the purpose. A weight in the form of a large stone or bags filled with soils is fixed to the shorter end of the lever. This weight acts as counterpoise to a bucket suspended by a rope or bamboo pole attached to the longer arm of the lever.
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Instead of the counterpoise weight, one or the two men walk back and forth along the top of the pivoted pole. The bucket could be a metal container or a leather bag. The device is operated by pulling down the rope or rod and bringing the container into the water and filling it. The counter weight helps in lifting the bucket. The bucket is emptied at the desired level. The working range of the counterpoise lift is generally between 1 to 3 m.
1. Archemedian Screw:
This device supposed to have been invented by Archimedes consists of a wooden cylinder with an augar like spiral. The spiral is made of short wooden boards or battens fitted on a control shaft, one end of which serves as a handle. The spiral on the control shaft is enclosed in a cylinder of wooden planks. The battens form a double helix and help in the movement of water from the inlet end of the cylinder to the outlet end.
The device is portable and is operated by one or two men facing each other in a sitting position. As the operators will have their feet submerged in water during the period of working, attack of water-borne parasites and consequent diseases have been reported from some countries where this device is used.
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Operating variables of the Archemedian screw consists of the head H, angle of installation, the screw diameter D, the shaft diameter d, the number of spiral blades, the speed of rotation n, and the pitch of the screws.
The diameter of the shaft is determined by the required strength of the screw. The length of the screw, the operating head H and the angle of installation are dependent on each other.
Each design has an optimum angle of inclination, generally in the range of 30° to 40°, depending on the pitch the diameter of the internal helix and the lift. The efficiency of the screw depends on its capacity.
For a given screw, the discharge and mechanical efficiency were observed to be maximum when the lower end of the screw was about half submerged in water. Modifications of Archemedian screw have been made for its operation by pedals as in a bicycle, or to be operated by an electric motor or engine.
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2. Chain Pump:
The chain pump consists of an endless chain, on which circular discs are provided at a distance of about 25 centimeters. The rotation of the drum makes the, chain along with the discs move inside a tube. When the movement of the chain is upwards, each disc brings up a volume of water and the water is discharged into a trough which in turn discharges into the outlet channel.
The discs are made of metal or leather washers strengthened by metal washers. The latter ones provide comparatively smoother operation. Chain pump operates satisfactorily upto 6 m lifts. The tube through which the discs pass is of 10 cm dia. and larger the diameter greater is the effort to operate the device. The chain pump can be adapted for operation with animal power by adding a driving mechanism.
3. Hand Operated Reciprocating Pump:
This pump, usually referred to as the Allahabad pump is a hand operated reciprocating pump. It has cylinder in which a piston is operated using a lever mechanism. The suction side is connected to a pipe which draws water from the source. This gives a discharge of about 3 to 6 litres per second with a static lift of 4 m.
4. Treadle Pump:
The treadle pump is a foot operated pump which uses a bamboo or PVC tubewell to extract water from shallow groundwater.
The pump has three parts, viz.:
(1) A metal pumphead,
(2) Two treadles and a frame, and
(3) A bamboo or PVC pipe and strainer.
The pumphead consists of two identical cylinders of sheet metal welded together with a suction inlet at the bottom and two plungers with rope and pulley. The discharge of this pump depends on the cylinder diameter and the suction head. It has been observed that with cylinder size of 152 mm and 2-3 m suction range the pump delivered 4 l/s of water.
Table 10.1 gives the output of different manually operated water lifting devices. There are some other manually operated devices used in several parts of the world. Some, of them are the paddle wheel used in China, tympanum in Vietnam and water ladder in Thailand.
Animal Powered Devices:
The animal powered devices can be broadly divided into two groups; those which use the principle of pulley, rope and bucket, and those that uses a rotating wheel or drum.
1. Rope and Bucket Lift:
This device consists of a bucket or bag of leather or canvas, attached to one end of a long rope. The rope passes over a pulley set in a suitable framework of wood installed over the well or other water source.
A pair or a single bullock is made to walk down a sloped earthen ramp while pulling up the full bucket or bag and walk back up the ramp after the bucket is emptied. The bucket is emptied into the outlet channel by a person, or a self-emptying bucket can also be used.
In the self-emptying bucket a spout is attached to the bottom of the bucket or bag. A light rope is fastened to the lower end of the spout. This rope passes over a roller on the receiving trough.
This rope is also attached to the bullock yoke and its length is so adjusted that the spout is in an upward position while the bucket rises up. When the bucket reaches top of the well, the spout follows the rope tied to it over the roller and the water in the bucket is discharged into the receiving trough.
The self-emptying bucket saves the labour of one person. The rope and the bucket lift are generally suited upto lifts of 10 m. The disadvantage of the device is mainly with its operation as the animals have to walk backwards up an incline while the bucket is lowered to the water source.
2. Persian Wheel:
The Persian wheel is one of the most popular animal drawn water lifting device. The main advantages are the rugged construction and reasonably good amount of discharge it provides. The parts are durable and generally need very little maintenance.
The device consists of an endless chain of buckets passing over a circular drum made from angleirons. The drum is rotated by a horizontal shaft which in turn is rotated by vertical and horizontal cogwheels. The large wheel has a pole extending from it horizontally. This pole is drawn by the animals moving in a circular manner.
The metal containers have a very small opening at their bottom to drain out the water in them and thus not to provide large starting load. The animals operating this device are sometimes blindfolded. This helps the animals to keep a steady pace, prevent them from getting giddy and also continue operation even when the operator is away temporarily.
3. Reciprocating Pump:
An animal drawn reciprocating pump was developed by Khepar et al., (1975). This pump uses two units of the Allahabad hand pump. The suction sides of both the units are connected to a pipe through a T-joint. The pipe ends in the source of water.
The units are driven by a gear mechanism similar to that of in the Persian wheel. The animals move in a circle to drive the gear mechanism. The main advantage of this pump is that the suction pipe can be placed in a shallow bore for water lifting. It is reported that this pump is capable of delivering water at a rate of 7 l/s with 6 m head.
Mechanically Powered Devices:
Mechanically powered devices for water lifting referred to as pumps provide much higher rates of discharges. Electrical motors, internal combustion engines, wind power, hydropower and solar energy are some of the sources of power which operate the pumps.
A pump is a machine which, when placed in a conduit, transfers energy from the external source to the liquid flowing through the conduit.
Pumps used for water lifting are broadly classified as follows:
1. Positive displacement pumps, which are further classified as –
(i) Reciprocating pumps, and
(ii) Rotary pumps.
2. Rotodynamic pumps, which are further classified as –
(i) Centrifugal pumps,
(ii) Turbine pumps,
(iii) Submersible pumps, and
(iv) Propeller pumps.
Drives for Pumps:
Four common types of drives are used in irrigation pumping.
These are:
(i) Direct drive,
(ii) Belt drive,
(iii) 90° gear head, and
(iv) Tractor belt pulley or power take off.
In the direct drive the prime mover and the pump have the same axis (Fig. 10.24a). This drive is the most efficient as there is no loss of power. But direct drive is limited to the condition where the speed of the prime mover is same that of the pump.
For horizontal centrifugal pumps, the direct drive may be either through a flexible coupling or a close coupling. While close coupling is convenient for alignment, flexible coupling has the advantage of removing the prime mover for its separate use.
Monoblock pumps have the same drive shaft for the motor and the pump. Since in case of direct drives, it is not possible to change the speed of the pump, care should be taken to select the right prime mover for the operating conditions under consideration.
(ii) Belt Drive:
Belt drives (Fig. 10.24b) are used when the pump and prime mover are to be located separately or when the speeds of the pump and the prime mover are different. Belt drives are either flat belt or V-belt. The V-belt drives have a higher efficiency than flat belt drives. However, they require specially designed pulleys and are suitable for shorter distances as compared to flat belt drives.
(iii) 90° Gear Head:
The 90° gear head drive is commonly used when an I.C. engine is used for operating a vertical turbine pump. The gear head is efficient and dependable as compared to the belt drive.
(iv) Tractor Belt Pulley or Power Take Off:
The farm tractor at times is used as a source of power for running centrifugal pumps for irrigation. Power can be taken from the tractor either through the belt pulley of the tractor, or the power take off.
In both the cases as the r.p.m. of the source of power may not suit the r.p.m. of the pumping unit, the drive has to be suitably designed to obtain the required r.p.m. Farm tractors are generally uneconomical for pumping as only part of their power is used either through belt pulley or power lake off.
Tubewell and Pump Efficiencies:
For obtaining maximum working efficiency from the tubewell and the pumps, proper selection of the pumps and the prime mover to suit the well conditions as well as care and maintenance of the pump and the tube well components are essential.
Some of the common items to be kept in view are as follows:
1. The suction lift should be periodically checked and it should be within the permissible limits.
2. The gland packing in the pump should be checked and replaced whenever necessary. The gland packing should be inserted in small pieces of length equal to the circumference of the pump shaft. The ends of two adjacent rings should not coincide. The water should drip through the packing at a rate of 15 to 30 drops per minute.
3. Periodical inspection of the impeller of the pump is necessary for wear. In case of cavity wells, small gravel is likely to get lodged in the impeller, reducing the capacity of the pump.
4. The r.p.m. of the prime mover should be at the rated value. Low voltage, improper pulley diameter and belt sag are some of the reasons for reduced r.p.m.
5. The alignment of the pump and motor shaft should be checked from time to time.
Electrical Connections:
When the prime mover used for pumping is an electric motor, it has to be properly installed and the wiring done as per electric codes. The most common type of electric motors used are the squirrel cage induction motors operated by 3 phase AC, 50 cycles and 400-440 volts. Single phase motors are used for pumps of small discharges (like domestic supply).
The 3 phase motors are connected to the power supply with 3 phase wires and a neutral wire.
The different items used in the connecting system are:
(1) Main switch,
(2) Energy meter,
(3) Voltmeter and ammeter,
(4) Indicator lamps, and
(5) Starter.
A shunt capacitor after the main switch is installed under certain circumstances.
A shunt capacitor is a device which improves the output of a motor by improving the power factor of the motor. The common cause of low power factor is the presence of a large number of induction motors in a line. Also, the characteristics of the induction motor are peculiar in that its power factor drops rapidly as the load goes down.
So, if a line from a transformer has large number of pumping sets run by electric motors and quite a number of them are working lightly loaded, the power factor is bound to be low. To counteract this, it is essential to install power shunt capacitor.
The supply lines are first connected to the main switch. It contains a lever to disconnect or connect the supply line and fuses of proper capacity for protecting the motor against any severe faults like jamming of the centrifugal pump, bearings of the motor or live line getting connected to the earth.
The energy meter records the energy consumed in kilowatt hours. The voltmeter and ammeter indicate the line voltage and current drawn. The indicator lamps show the supply through the 3 phase. The voltmeter, ammeter and indicator lamps are optional and are not necessary in every installation.
The starter is an important component in the installation. For single phase motor a simple switch is used for starting and stopping the motor. For 3 phase motors, a direct on line starter or push button starter is used up to 5 HP motors and star-delta starters from 5 to 15 HP and oil immersion type starters beyond 15 HP.
The purpose of the starters is to protect the motors against overloading and single phase failure. In either case the line supply is disconnected. The star-delta starter provides reduced voltage at the time of starting. At starting the supply is connected to motor which has star connections then and the line voltage is reduced 1/√3 phase voltage. The starting phase current is thus reduced in the same proportion.
Thus the motor is protected against heavy in rush of starting current. The motor has three coils one each for each phase of supply. The six terminals of the motor are of these coils and are connected to the star-delta starter.
For starting, the starter lever is pressed down and the supply is connected to the motor with its coils connected star. After the motor accelerates, the lever is pressed up changing the motor coils connection from star to delta and supplying the full voltage to the motor.
Hydro Power for Pumping:
The energy of flowing water can be used for operating water lifting devices. These devices are useful in remote areas where other forms of energy are not readily available.
Two devices which use the energy of flowing water ate described herein:
1. Hydraulic Rams:
The hydraulic ram is a water lifting device that does not require an external, source of energy. This device uses the dynamic pressure of water flowing under a low head to lift a portion of this water to a higher head.
The elements of hydraulic ram are shown in Fig. 10.26. It consists of a supply pipe connected at its upper end to a supply reservoir, and its lower end to a valve box O. The valve box has two automatic valves, a waste valve B opening downwards and a delivery valve A opening upwards.
Above the delivery valve is an air vessel F, to the foot of which the delivery pipe D is connected. When the waste valve is opened, the water from the supply pipe begins to move and starts overflowing through the waste valve.
As the rate of discharge through the valve increases, due to the acceleration of the water column in the supply pipe, the pressure head in the valve box begins to rise. It reaches a value at which the total force acting on the lower face of the waste valve is greater than the downward force due, to the weight of the valve.
At this point the waste valve gets closed. As soon as the waste valve gets closed, the pressure continues to rise, the delivery valve is forced to open and the water flows straight through from the supply tank into the air vessel and the delivery pipe. The flow continues until the original kinetic energy of water column in the supply pipe is exhausted.
At this point, the pressure in the valve box momentarily falls below atmosphere, permitting the waste valve to open automatically and the cycle of operation is repeated. During this brief period of negative pressure, a small quantity of air is drawn into the valve box through a small orifice in order to keep the air vessel charged.
The air vessel helps in maintaining a continuous discharge through the delivery pipe-although water flows intermittently through the delivery valve, by temporarily storing the excess water above the mean discharge.
Installation of hydraulic ram is not possible under all circumstances. Natural topographical conditions should be favourable for the installation of hydraulic ram. Hilly areas are suitable for this device. As can be seen only a part of the water from the supply reservoir is delivered and the rest escapes through the waste valve.
2. Water Turbine Pumps:
The water turbine pump is a water pumping machine consisting of a turbine and a pump. The turbine is driven by hydraulic energy and the pump lifts the water. A coaxial water-turbine pump which works below water surface is shown in Fig. 10.27.
Lower half section of the water turbine pump is a turbine (axial flow) and upper one a centrifugal pump. It requires a certain head of water at upstream for its functioning.
A certain amount of water passes through turbine and puts it into rotation. The rotating runner drives the impeller which is mounted on the same shaft with runner. By the action of centrifugal force of the impeller the water is drawn in and throughout continuously, collected by the volute casing, and flows through delivery pipe. The water turbine pump may be single or multistage depending upon the lift required.
Efficiency of Water Turbine Pump:
Wind Power for Water Pumping:
In areas where wind velocities are sufficient (6.5 km/hour on average and above) wind mills can be operated for water lifting purposes. Wind mills are driven by the power of natural winds. The wind mill consists of a large diameter vane wheel or rotor fixed on the top of a high steel or wooden tower. Usually a reciprocating pump is operated by the wind mill.
The main disadvantage is that the functioning of the wind mill may not exactly coincide with the need for water. As such suitable provisions for storage of water are needed. Wind mills could generally be used for operating pumps for domestic water supply or for irrigating small areas.
The recent trend is to establish ‘wind mill parks’ wherein several wind mills are installed at one location and are used for generating electric power. Hirshberg (1982) provides the details of wind mills for water pumping.
Solar Energy for Pumping Water:
Utilization of solar energy for pumping water offers immense scope. However, large scale applications of the same have not so far been reported. Limited success for utilizing solar energy for water pumping has been achieved. Solar energy is converted to electrical energy through photo-voltaic cells and the electrical energy is used in running a motor and pump. The size of pump to be used depends upon the number of photo-voltaic cells.
Example:
Calculate the size of the electric motor needed to be used with direct coupling with a centrifugal pump installed with the following conditions –
Static Suction head = 5 m
Efficiency of pump = 60 per cent
Static delivery head = 10 m
Efficiency of motor = 90 per cent
Amount of water needed in 12 hours = 9 ha cm
Solution:
