Soils 456 Laboratory 10

 

Title : Drip irrigation Laboratory

Objective:To familiarize the students with Drip irrigation design

Drip Irrigation

Procedure: Design a garden consisting of small plots 20 ft by 40 ft with 5 ft walk ways between the garden plots. The area is the field next to the trailer at the Horticulture farm. The crops to be grown are annuals only. The crop can vary from onions to flowers so design the system to supply water sufficient to satisfy maximum evapotranspiration plus 20 % . The plots will be irrigated from daily to every three days. The drip tubing will be tubing having a flow of 40 gph/ 100 ft of tubing. Each plot need a minimum of one hand valve and one solenoid valve. The system should have one screen filter and the field should be divided into blocks, each block have a pressure regulator on it. A general layout of a drip irrigation system consists of a filter,control valve and pressure regulator , submain manifold and drip tubing. Row 40 inches.

Greenhouse

 

 

water source (ws) located NW corner of field with 65 psi of pressure. Water source is 6 inch main line from city. 

                                                (ws)

 

 

Trailer

North

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The system need to be designed for maximum water use per day and a reasonable expectation is that the irrigation water will be applied every three days. Another reasonable assumption is that every one irrigates at the same time and that they will not want to irrigated for more than 12 hr.

1. Check the flow rate of the tape to determine the time that the system needs to be turned on

Et= 0.45 inch/day max.

Flow= 40 gph/100 ft = 0.66 gpm/100 ft

Furrow spacing 3.5 ft . Area 100ft *3.5ft= 350ft^2/43560ft^2/ac=0.00803 ac.

qt=ad
q= cfs
t=hr.
a= ac
d=inches.

0.66 gpm/450 gpm/cfs= 0.00146cfs

d= 0.45* 3=1.35 inch/efficiency(0.8)= 1.68 inch for three days

0.00146 t=0.00803*1.68, t= 9.5 hr. Flow rate of tubing selected can be as low as 20 gph which means that the system will have to run. 40/20=2 time or 19 hr. Need to select high flow rate of tubing.

Flow rate of system = length of tubing * flow rate of tubing.

Area 140ft* 100 ft= 14000ft^2/43560= 0.32 ac
d= 1.68
t= 9.5 hr
qt=ad

q= 0.32*1.68/9.5 *450= 25gpm

If tubing is not installed in walk ways then the number of lines is 12 per block with three blocks. The drip tubes will cross the walkways between each 20 ft block. Number of block is 3  blocks of 40ft width or 36 lines. Each line is 0.00146 cfc. Total flow is 23.5 gpm. 

 

Design pipe network for 25 gpm. Input pipe size should be 1.5 inches for main manifold.-

Number of outlets is  36

Schedule 40 pipe. Friction loss = 1.62 psi/100 ft * 140 ft * 0.349 =0.79psi.

If operating pressure of drip tubing is 12psi and friction loss is 0.79/12=  6% then you can install a pressure regulator at the head of the main pipe. 

Layout of system. 

Main line- globe valve- back flow prevention valve- flow meter - fertilizer injector -   screen filter - electrical valve- pressure regulator-  air and vacuum  release valve.  

 Globe Valve specification .  Install manual valve 1 1/2  globe valve friction loss is  1.5 psi

Black Flow prevention valve specification . . PVB type   1 inches friction loss  4 psi

Flow meter  specification . 1.5  inch disk type water meter  friction loss 1.3 psi

Fertilizer inject specification . (http://www.berryhilldrip.com/Dosatron.htm) dosatron model Model D8R friction loss not given estimated at 3psi

Screen Filter specification  (http://www.berryhilldrip.com/FilterPr.htm) NET25A15140 1.5 inch 200 mess friction loss estimated 3psi

Electrical valve 1.5 inch pressure loss 1.7 psi page 93 book 

Regulator specification             Install 1 1/2" Standard  NETAFIM #32PRV1.5   12 PSI order 12 psi spring ( http://www.berryhilldrip.com/RegulatorPg.htm). The regulator will not work a less than 25 psi inlet pressure.

Air vent  1.5 inche APV http://www.agproducts.com/products/arvr/arvr.pdf. no friction loss. 

Total friction loss from water source to regulator   14 to regulator  needed pressure 25+14= 39 have available 65 . System will work ok. 

Controller  specification to turn on system for fix time. Rain bird controller  model ESP four station. ( http://www.sprinklerwarehouse.com/)

 

Alternate design is to put sub main for three block and pressure regulator on each submain. Design this system.