welcome

PRESSURE VARIATION ALONG DRIP IRRIGATION SYSTEM

PRESSURE:

Pressure is a form of energy imparted on the molecules of water.

The pressure is the force applied by a fluid on a surface.

or

PRESSURE VARIATION ALONG DRIP IRRIGATION LINE:If the drip irrigation line is laid on slopes , slopes will affect the pressure variation.Pressure change due to elevation

When the line is laid upslope , it will loose pressure and

PB=PA-∆H-∆S

When the line is laid down slope , it will gain pressure

PB=PA-∆H+∆S

➢ The loss or gain in pressure is linearly proportional to the slope and length of the line.➢ This can be expressed as follows ( Wu & Gitlin , 1974 )

dh/dl = sf = +_ soWhere Sf = energy slope , the slope of

the energy gradient lineSo = line slope

Pressure measurement in a flowing pipe:

When water flows in a pipe , the pressure head at any point can be easily found by inserting a vertical pipe called piezometer as shown in fig.

PRESSURE LOSS DUE TO FRICTION:

➢ When water passes through a horizontal pipe , water looses pressure along the direction of flow.➢ This is because of friction between the water if the pipe material and also friction between water molecules.HEAD LOSS DUE TO FRICTION:

THERE ARE TWO EQUATIONS AVAILABLE FOR FRICTIONAL LOSS CALCULATIONS. ✓ Darcy-weisbach✓ Hazen-williams equation FRICTION LOSS

QQ

Friction loss in plain pipes

S.NO PIPE MATERIAL FRICTION COEFFICIENT (C)

1. Plastic 150

2. Epoxy coated steel 145

3. Cement asbestos 140

4. Galvanized steel 135

5. Aluminum &steel 130

6. Steel (or)concrete 100

Values of Hazen williams C

DESIGN CRITERIA FOR DRIP IRRIGATION SYSTEM BY USING NOMOGRAPH

Design criteria for drip irrigation system

➢ There is no definite rule about the design criteria for drip irrigationFor most of the designers are using below

✓ for design criteria laterals for emitter flow variation is 10%✓ for design criteria sub mains for lateral flow variation is 10%,then emitter flow variation for whole field is20%.This will give an application efficiency of 90% for whole filed

➢ When the sub mains is designed with less than 10%lateral flow variation ,the application efficiency of the whole filed will be larger than the 90%.

➢ IN CASE, the lateral is designed for 20% emitter flow variation emitter flow variation and sub main is designed for a10% lateral flow variation , the over all irrigation application efficiency still will be about 85%.

Hydraulic variation calculated based on highest and lowest pressure in the pipe. This equation for the finding out the hydraulic variation. HERE Vh =hydraulic variation Hmax=max pressure in sub mains or laterals Hmin=min pressure in sub mains or laterals h=avgpressure in sub-mains or laterals

✓ For lateral design,the allowable hydraulic variation is 20%

✓ For sub main design,the allowable hydraulic variation is 10%

STATISTICAL VARIATION OF PRESSURE It is find out by the coefficient of variation of pressure in the pipe Where n is the no of drippers or laterals ➢ For lateral design, the allowable statistical variation is 7%➢ For sub mains design the allowable variation is3.5 to7%➢ The relation ship between Vh and Vs Vh=0.86+3.0378xVs-0.0194705Vs

➢ In case of laterals are laid upslope, the maximum pressure head at the start of the laterals and minimum pressure occurs at the end of the lateral

➢ In case of laterals and sub-mains are laid in down slope, the location of minimum pressure and maximum pressure may be any where in the pipe depending on the magnitude and of friction loss and elevation gain along the flow

•To use these figures for the design following procedure is used .

• First , deside on a lateral length (L)and an operating pressure head at the start of the lateral(H).• Find out the ratio L/H in vertical axis . • Move horizontally till you cut the slopes percent of the land• Then move upwards into the first quadrant, till the desired location of hydraulic variation in quadrant -1.

➢ Then Draw horizontal line into quadrant -2.➢ Then mark L/H horizontal axis.➢ Draw vertical line from the point➢ Both lines will intersect at a point ➢ Find out the value of ΔH/L corresponding to the point.➢ For this value, find out the design diameter using the nomograph given below

• Note: The nomogram is based on the Prandti - Coalbrook formula using a k factor of k= 0.007 mm. Factors applicable to other flow formulae are: Hazen Williams c = 150, Manning n = 0.010 and Darcy roughness factor, = 0.007

Design for drip by using nomograph

Presented by:SwapnaPriya . S. v.Pavan Kumar . c