Agricultural Engineering
· “Counter poise lift” is commonly used to lift water from shallow wells.
· “Rope and bucket lift” is the most common water lift in India to draw water from deep wells.
· Centrifugal pump mainly consists of two parts.
1. Impeller (or) rotor: Which add energy to the water in the form of increased velocity and pressure.
2. Casing: Which guides the water from the impeller.
· Classification of centrifugal pumps.
1. Depending upon energy conversion.
a. Volute
b. Diffuser
2. Plane of rotation of the impeller.
a. Vertical
b. Horizontal
3. Type of impeller
a. Open
b. Semiopen
c. Closed
d. Non clog.
4. Number of stages
a) Single stage
(b) Multi stage.
5. Section
a. Single
b. Double
6. Method of drive
a. Direct driven
b. Belt driven
· In diffuser pump velocity head converted to pressure head.
· In ‘vertical centrifugal pump’ the suction lift of the pump should not exceed 4.5 to 6.0M.
· Where the shalf leaves the casing, there is a gland (or) stuffing box to prevent leakage of air.
· ‘Bed plates’ – For mounting the pumps and to fix properly on the foundation for avoiding vibrations.
· Foot valve – The main purpose to retain water in the pump.
· Priming – The process of removing air from pump casing and suction pipe.
· The interrelationship of capacity, head, power and efficiency are best shown by graphically and these curves are called “Characteristic curves of the pump”.
· When the speed is kept constant ‘Capacity decreases’.
· ‘Sluice value’ is provided to have smooth flow.
· Pump capacity Q = 28 AD / EH
Q = discharge in lit/sec’
A = Area in ha.
D = Gross depth of irrigation in cm.
E = Number of days for irrigation
H = Number of hours of operation
· Static head” is the vertical distance between the water surface at the source and at the outlet.
· ‘Static suction head” is the vertical distance between the water level and the centre line of the pump.
· Static discharge head: Is the vertical distance between the centre line of the pump and the point of free delivery of water.
· Static head = Static suction head + Static discharge head.
· Friction head = is the head required to overcome the resistance of the pipeline and fitting.
4flv2
hf =—————
2gd
f= Co-efficient of friction
l = Length of pipe in ‘m’
d = diameter of pipe
g = 9.81 m2/s
· Velocity head: Velocity head is the distance through which the liquid must fall to acquire
a given velocity.
v2
ℎ =————–
2g
· Total head = Static head + Friction head + Velocity head.
Discharge in (lit/ sec.) X total head in (meter)
· Water house power (WHP) =_______________________________
75
Discharge in (m3/ sec.) X total head in (meter)
=______________________________
273
WHP
Shaft HP (SHP) =________________
Pump efficiency
WHP
Brake HP (BHP) =_______________
Pump efficiency X drive efficiency
WHP
Input HP =________________
Motor efficiency
Overall efficiency = Pump efficiency X drive efficiency.
· Reciprocating and centrifugal pumps are the examples of shallow well pumps.
· The principal advantage of the submerisable pump is that it can be used in a ‘very deep tube wells’. These are adopted to tube wells of 10 cm diameter.
· Submerisable pump has no working part above the ground.
· Wetted perimeter: Sum of the lengths of sides of channel which are in contact with water.
· Hydraulic radius: It is the ratio between cross sectional area of the stream and the wetted perimeter.
· Free board: Is the expected vertical distance between highest water level and the top of the retaining banks. It is provided to prevent over topping of structures because of “Wave actions”. Generally 20% of the designed depth is taken as free-bard.
R2/3 S1/2
· Open channel velocity V = _______________(Manning’s Formula)
n
S = Hydraulic slope
R = Hydraulic radius
n = roughness coefficient
A= Cross sectional area
Discharge capacity Q=A.V.
· The best hydraulic section of a trapezoidal channel under favorable structural condition
b = 2d tan θ/2
b = bed width
d = depth of flow of water
θ = angle b/n side and the horizontal
· Lining material – Concrete; LDPE sheets.
· Underground pipes:–
P1 pipe – up to 8m head ; P2 pipe – up to 8m – 20m;P3 pipe – >20m head.
· ‘If sulphates are high’ concrete pipes should be avoided.
· ‘Plastic pipes’ are specially suitable in the smaller diameter for about 6 kg/cm2 high pressure.
· Irrigation piper are tested
1. For water absorption.
2. For strength
· To test the water absorption samples of the pipe are boiled for about 5 hours and gain in
weight by moisture absorption is notes.
· The standard irrigation pipe should not exceed 8% of the original dry weight.
· The discharge through a pipe line can be determined by applying the Darcy’s equation.
· Spacing of the pipes – Closer spacing’s are suitable for sandy soils and farther spacing
for heavy clay soils.
· To prevent damage of pipelines, they must be kept at least 45cm below the ground. The width of the trench should be 70cm for working convenience.
· The minimum diameter of the ‘Pump stand” should kept not less than 60 Cm.
· “Current meter” is an instrument which records number of revolutions corresponding to velocity.
· A weir is a notch of regular form through which water may flow.
· The bottom edge of weir notch is termed as the “Weir crest”.
1. Rectangular weir:
a. Suppressed rectangular weir: It has crest length equal to the width of the channel. The discharge Q = 0.0184 LH3/2.
b. Contracted Weir: It has crest length less than width of the channel. Q = 0.0184 (L – 0.1nH) H3/2
n = Number of end contractions
· Sharp crested weirs are preferred over “broad crested weirs”
Trapezoidal weir (cipolletic weir) ; Q = 0.0186 LH3/2
Triangular weir Q = 0.0138 H3/2 (To measure low discharges)
· Parshal flume – It is having 3 sections.
1. Converging (or) Contracting section – leveled
2. Constricted (or) throat section – Down ward
3. Diverging (or) expanding section – Slope upward.
· The size of the parshal flume is expressed by the width of the “throat”.
· Sandy soils and Sandy loam with high infiltration will have smaller basins and clay soils with low infiltration large basins.
· Check basin method is suitable to most soils except to sandy soils.
· All row crops included grains, Vegetables and various cash crops are adopted to ‘contour furrows’ method. Contour furrows are not advisable in sandy soils and soils that crack.
· “Sprinkler irrigation” is not suitable in very fine textured soil where the infiltration rate is
less than 4 mm/hour.
· Drip irrigation method is accomplished by using small diameter plastic lateral lines with
devices called “Emitters (or) Drippers”. In drip irrigation the capacity = 2 -10 lit/hour.
· “Plastics” is an organic substance and it consists of natural (or) synthetic binders (or) resins with (or) without moulding components.
· Elastomers: These plastics are soft and elastic materials with a low modulus of elasticity. They deform considerably in tension and the deformation disappears rapidly at room temperatures.
· Indathene: is the trade name of various grades of LDPE manufacture and marketed by IPCL (Indian petro chemicals corporation limited).
· Water erosion is of four types
1. Sheet erosion
2. Rill erosion – This is advanced stage of sheet erosion.
3. Gully erosion – Gully erosion is the removal of soil by running water with formation of chemicals, that cannot be smoothed out completely by natural condition cultivation. Gully erosion is an advanced stage of “Rill erosion”.
4. Stream channel erosion – Transportation of soil along the banks of stream.
Sheet → Rill → Gully → Stream channel
· The rational method is commonly used in predicting peak-run off rate of small water sheds. (< 1300 ha.).
Q = 0.0276 CIA.
Q = Peak – runoff in cum./sec.
C = Run off coefficient
I = Rainfall intensity in cm/h
A = Watershed area in ha.
· “Bench terracing” is one of the oldest mechanical (or) engineering method of erosion control. This will be useful in soils with slopes more than 15%.
· Types of bench terraces.
1. Level and table: They are suitable for areas receiving medium rainfall which is evenly distributed and which have highly permeable and deep soils.
2. Sloping outwards: They are used in low rainfall areas with permeable of medium depth.
3. Sloping inwards: They are used in heavy rainfall areas.
· Broad base terracing: Classified into
1. Graded terrace – Useful on poorly drained soils with slopes less than 4%.
2. Level terrace – on slope of <2%.
· From functional aspects, graded terraces are classified as “interception”.
· Terraces are further classified in to
1. Channel type
2. Ridge type.
· Channel type is mostly used on soils where controlled removal of water is of prime importance. It is built from one side.
· Ridge types are usually used where the water holding capacity is principal function. It is built from both sides.
· Surveying is a process of determining the position of points in a horizontal plane.
· “Leveling” is the art of determining and representing the relative heights.
· In “geodetic survey” curvature of the earth is taken into consideration.
· “Plane survey” – taken for smaller areas.
· Radian is the unit of plane angle
· In approximate results, distance may be determined by “Pacing” (average length of pace– 80cm).
· In ‘Computative method’ distances are obtained “Calculation”.
· Swivel joints are provided at the end of the chain to turn round without twisting.
· For work of highest precisions “Invar tape” is generally used.
· In ‘Optical square’ H & I mirrors are placed at an angle of 450.
· The mirror H called horizon glass is half silvered. The mirror ‘I’ known as ‘index glass’ is whole silvered.
1. If both ends are visible from intermediate points “Direct ranging” is practiced.
2. If both ends are not visible from intermediate points “Indirect ranging” (or) Reciprocal ranging”.
· The principle of chain survey is ‘triangulation’.
· A number of subsidiary lines called “Tie lines”.
· The longest of the chain line – “Base line”.
· Joining the apex of triangle – “Check line”.
· The positions of boundaries, building, fences – “offsets”.
· The preliminary inspection of area to be surveyed is called “Reconnaissance” survey.
During this survey prepare a neat sketch called “Index sketch”.
· Reference sketch: are necessary to find the positions of stations.
· Type of impellers in turbine pump – Closed and semi open.
· The most accurate method of finding areas between chain line and curved boundary is “Simpson’s rule”.
· The first reading – back sight, Last reading – Foresight, In between reading – Intermediate signt.
· Silting takes place if the channel slope is less than 0.05%.
