## HYDRAULICS_4
## DESIGN OF IRRIGATION SYSTEM __Options__
## The rule of 20% is applied to all the sprinklers on the same subplot. Any excess pressure over 20% between subplots is controlled by flow pressure regulators. ## The rule of 20% is applied to a single lateral, and pressure regulators control the difference pressure between the laterals.(It is common in drip systems.) ## The difference pressure along the lateral exceeds the 20% head loss by any desired amount. Flow regulators inside the emitters or pressure regulator in the sprinkler riser control the excess pressure. (It enables the use of a longer lateral pipe or smaller diameter than permitted by options 1 or 2.)
## A PE lateral pipe with 10 micro-sprinklers is spaced 10m ## apart. The first sprinkler is 5m away from the inlet of lateral. ## The flow rate of selected sprinkler is qs=120l/h, the required ## pressure head is hs=20m. The riser height is 0.15m. What ## is the appropriate lateral pipe diameter if options 1, 2, and 3 ## are taken into consideration? ## The length of lateral is as follows: ## The flow rate of the lateral pipe is:
## DESIGN OF IRRIGATION SYSTEM **Option 1**
## For a 20mm PE pipe the hydraulic gradient out of a slide ## ruler or monograph is J=19%. ## 3. The head loss of a 20mm plain PE pipe is ## The head loss for 10 sprinklers is as follows where coefficient F10=0.384: ## Since hfhmax=0.2 hs the diameter of lateral pipe is too small.
## DESIGN OF IRRIGATION SYSTEM **Option 1** ## For a 25mm PE pipe the hydraulic gradient out of a slide ## ruler or monograph is J=6.2%. ## 5. The head loss of a 25mm plain PE pipe is ## 6. The head loss for 10 sprinklers is as follows where coefficient F10=0.384: ## Since hf<hmax=0.2 hs the diameter of lateral pipe is good. ## 7. The required inlet lateral pressure is:
## DESIGN OF IRRIGATION SYSTEM **Option 2** ## The permitted pressure variation along the lateral can be 4m, ## used. The applied pipes are 25mm and 20mm diameter ## ones. *Pressure regulators will be installed by the inlets of laterals* to
## compensate greater head loss than 20%. ## Let the first 25mm diameter pipe be along 35m (n25=4) and 20mm diameter pipe be along 60m (n20=6) as it can be seen below:
## DESIGN OF IRRIGATION SYSTEM **Option 2** ## 2. The flow rate for 25mm pipe along 60m is calculated as follows: ## 3. The hydraulic gradient out of a table or slide ruler for 25mm pipe and flow rate of 0.72m3/h is 2.5%.
## DESIGN OF IRRIGATION SYSTEM **Option 2** ## 4. The head loss for 25mm pipe along 60m is as follows: ## 5. The head loss for 6 sprinklers is as follows where coefficient F6=0.458: ## 6. Previously the head loss for 25mm pipe along 95m, 10pcs of sprinklers and Q=1.2m3/h has been computed which was 2.261m (see Option 1), then the head loss for 25mm pipe along 35 with four sprinklers is
## DESIGN OF IRRIGATION SYSTEM **Option 2** ## The flow rate for 20mm pipe along 60m with six sprinklers is as follows: ## The hydraulic gradient out of a table or slide ruler for 20mm pipe and flow rate of 0.72m3/h is 8%. ## The head loss for 20mm pipe along 60m is as follows: ## The head loss for 20mm pipe with six sprinklers is:
## DESIGN OF IRRIGATION SYSTEM **Option 2** ## The total head loss along the combined lateral pipe with 35m length of 25mm pipe and 60m length of 20mm pipe is as follows: ## Since hf,95<hmax=0.2 hs the diameter of lateral pipe is good. ## 12. The required inlet pressure by the last lateral is:
## DESIGN OF IRRIGATION SYSTEM **Option 3** ## or pressure regulators in every emitters, the sprinklers or ## the drippers. ## Therefore, the diameter of pipe can be reduced. The cost ## energy and regulators. ## Principal theory of Option 3 is that *unlike Option 1 and * *Option 2, in case of Option 3 the entire head loss along *
*lateral pipe is added to the lateral inlet pressure.*
## In case of 20mm diameter, the head loss* hf*=6.93m (see Option 1). ## Therefore, the required inlet pressure of the lateral pipe is as follows:
**References **
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