WATER LIFTING DEVICES
According to power sources water lifts can be classified as manual, animal and power operated devices. The brief description of these devices is as under:
Human Powered Devices
Man has a limited physical power output, which may be in the range of 0.08 to 0.1 hp. This power can be used to lift water from shallow depths for irrigation. The common man powered
devices are:
1. Swing basket.
The device consists of a basket made from the cheap materials like woven bamboo strips, leather, or iron sheet to which four ropes are attached. Two persons hold the basket facing towards each others, dip the basket in water source and by swinging, the basket is lifted and filled in water course from where the water flows to the fields. The device ~s useful up to a depth of O.15 m and discharge may vary from 3500 to 5000 l/h.
2. Counterpoise lift.
It is also known as dhenkli or picottach. It is generally used for lifting of water from unlined wells, stream or pond for irrigating small fields. It consists of a lever rod supported at a suitable point on a vertical post about which it can swing in vertical direction. About 2000 1itres of water can be lifted from the depth of 2 to 3 meters in one hour.
3. Don.
The principle of operation of don is similar to counterpoise lift. The don consists of a trough made from wooden log or iron sheet; closed at one end and open at the other. The open end of the trough is connected to a hinged pole with a counter weight through rope. For operation the trough is lowered by exerting pressure on it by pulling the rope and also by foot of the operator till the closed end is submerged in water. Upon releasing pressure the trough comes to its original position due to action of counter weight along with water. Water can be lifted from this device from a depth of 0.8 to 1.2 m.
4. Archimedean screw.
It consists of a helical screw mounted on spindle, which is rotated inside a wooden or metallic cylinder. One end of the cylinder remains submerged in water and is placed in inclined position at an angle of 30 degrees. It is used for lifting of water from a depth of 0.6 to 1.2 meters and may discharge 1600 liters per hour.
5. Paddle wheel.
It is also known as Chakram and is mostly used in coastal regions for irrigating paddy fields. It consists of small paddles mounted radially to a horizontal shaft, which moves in close fitting concave trough, thereby pushing water ahead of them. The number of blades depends on the size of wheel, which may be 8 for 1.2 m and up to 24 for 3 to 3.6 m diameters. The wheel having 12 blades may lift about 18000 liters per hour from a depth of 0.45 to 0.6 m.
Animal Powered Devices
Animal power is abundantly available in India. They are used for lifting of water, besides other field operations and processing works. A pair of bullocks may develop approximately 0.80 horsepower. They can Ii ft water from the depth of 30 m or more. Of course the rate of discharge will go down with increase in lift. Some of the devices used for irrigation operated by animal power are as under.
I. Rope-and-bucket lift:
Also known as Mote. Charsa or Pur it is used to lift water from lined wells up to a depth of 30 m. The device consists of a bucket or bag made of GI sheet or leather, and pulley arrangement. A rope is attached to the bucket-or bag, which passes over a pulley and finally fixed to the yoke of bullocks. The bullocks walk down on an earthen ramp sloped at an angle of 5-10 degrees to lift the water. About 9000 1itres of water can be lifted per hour with two pairs of bullocks with this device from a depth of 15 m.
2. Self-emptying bucket:
The arrangement is similar to rope and bucket lift device. The system consist of a leather container shaped like a funnel which has a spout on the lower end and the upper portion resembles to a conical cylinder. The container is open from both ends. The capacity of container may range from 100 to 150 liters. The device is suitable when the lift does not exceed 9 m at which discharge is about 8000 liters per hour.
3. Two bucket lift:
In this device two buckets are raised and lowered alternately. The bullocks move in a circular path and with the help of central rotating lever, rope and pulley arrangement the buckets move up and down. Each bucket may have carrying capacity up to 70 liters. The buckets are provided with hinged flap at the bottom, which acts as a valve. Guide rods are provided in the well for the movement of buckets. The buckets are automatically filled and emptied during operation. The device is suitable for lift up to 5 m at which discharge may be 14000 liters per hour.
4. Persian wheel:
It is also known as Raha. It is used to lift water from a depth up to 20 m. The efficiency of the device is considerably reduced after 7.5 m. The device consists of endless chain of buckets made of GI sheet having capacity from 8-15 liters. The chain of bucket is mounted on a drum and is submerged in the water to sufficient depth. The drum is connected to a toothed wheel held in vertical plane by a long shaft, which is usually kept below the ground level. The vertical toothed wheel is geared with a large toothed horizontal wheel connected to a horizontal beam. This beam is yoked to a pair of animals. For operation the animals move in rotary mode that rotates the buckets carrying water through the gear system. The water IS released when the bucket reach the top. Average discharge of Persian wheel is about 10,000 liters per hour from a depth of 9 m with one pair of bullocks.
5. Chain pump:
The chain pump is used to lift water from shallow wells and works most satisfactorily when the lift is about 6 m. The pump consists of an endless chain on which discs are mounted at the interval of about 25 cm. The endless chain usually passes over two drums. The upper drum is above the top of well to which axle and handle is attached for operation. The chain with disc passes through a pipe, which is about 10 cm in diameter and extends downward from the top of well to about 0.6 to 0.9 m below the surface of water. The discs on rotation of chain entrap the water and carry it to the top, which is discharged into the trough. The pump can be operated either manually or by animals having the system as that of Persian wheel.
Hydraulic ram
Hydraulic ram is a device to lift the water without any prime mover by utilizing the kinetic energy of flowing water. In this system the impact of water is converted into shock waves, which is called water hammer. This energy is utilized for lifting of water. The essential components of the system are check dam, supply pipe, hydraulic ram, storage tank and discharge pipe. Except for changing of washers in the valves, there is no repair and maintenance required and the ram can operate 365 days in a year without any trouble. For fixing a hydraulic ram a check dam is constructed on flowing water of a river, streams or nullahs to create low head. Due to velocity and pressure of the water, the valve of the ram closes suddenly which creates a water hammer in the system. This causes building up of high pressure, which opens the tank valve and water rushes to the tank. The tank is enclosed from all sides and the air present in it creates further pressure on the water, which enters the tank and closes the valve of tank thus discharging water from it. This discharged water is lifted by the hydraulic ram to higher head than the supply head. During this action part of the water in the supply pipe also starts flowing in reverse direction and the water valve is opened due to its own weight and the water again starts running in supply pipe. This action continues unless the action of waste valve is stopped. The magnification factor of head and efficiency of hydraulic ram can be known by the following formula:
q x h=Q x H x e
q = amount of water lifted by the ram,
h = head to which water is lifted,
Q = amount of water supplied to supply pipe,
H = head due to which water enters the supply pipe, and
e = efficiency of the ram.
The efficiency of the system depends upon h/H, which is called magnification factor. Table
below provides some values of magnification factor and efficiency.
Magnification 3 4 5 7 8 10 15 20 30
factor h/H
Efficiency 85 80 75 70 65 60 55 40 35
The pressure in the supply pipe depends upon amount of water, which enters in it. More the water enters,m ore is the velocity and water hammer effect. The researchers have optimized the inclination of supply pipe to 7 degrees at which the ram gives highest efficiency of 73% at magnification factor of 2.57 and discharge rate of 0.84 l/s. If the magnification factor is less and waste valve opens and closes more number of times per unit time, the ram will have higher efficiency. Generally if the waste valve opens and closes 44 to 60 times in one minute, the working of ram can be considered satisfactory.
Mechanically- Powered Water Lifting Devices
Mechanically powered water lifting devices are usually termed as pumps, which are operated with the help of auxiliary power sources such as engine or electric motor. These pumps are capable of lifting large quantity of water to higher heads and are usually employed for the irrigation of horticultural crops. Basically there are four principles involved in pumping water
(1) atmospheric pressure
( 2) centrifugal force (3)
positive displacement
(4) movement of column of fluid caused by difference in specific gravity.
Pumps are usually classified on the basis of operation, which may employ one or more of the above principles.
The pump can be classified as:
1. Displacement pumps: Reciprocating and rotary
2. Centrifugal pumps: Volute, diffuser, turbine, propeller
3.Airlift pumps.
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