Sprinkler heads changes according to properties of cross-sectional area of orifice, operating pressure and processing property of orifice. Because of head losses, sprinkler head loses pressure as goes from beginning of lateral towards to end of lateral. Therefore decrease in flows occurs (Anonymous, 2010). Difference of maximum 10% in flow and 20% in pressure across lateral line should be allowed to provide a suitable corresponding water distribution. Sprinkler flow is calculated by help of formula below
q=3600C AV (2gh) (10)
Where. Q:Sprinkler flow m3/h C:effective coefficient (0.80-0.95)
A: nozzle cross-section area m2 g:gravitational acceleration m/ s2 h:operation pressure of sprinkler head. m.
5.1 Precipitation rate
It is defined as water amount given per unit time in irrigation area (Connelan. 2002). It is generally expressed as mm/h. Main factors which affect precipitation rate are sprinkler flow, distance between sprinkler and distance between laterals. The average precipitation rate is calculated with the following equation.
Pr=1000*q/S*L (11)
Where.
Pr:The average precipitation rate. mm/h
1000: a constant which converts meters to mm.
q:the total flow applied to the area by the sprinklers. m3/h
S:the spacing between the sprinkler along lateral. m
L: The spacing between rows of sprinkler. m
The flow rate of sprinkler heads automatically changes in case of their making irrigation in different angles. For example, when sprinkler angle decrease from 360° to 180° degree, flow rate increases doubled. Therefore in the system where heads having different angle values are used, the average precipitation rate is calculated by means of the following formula.
Pr=360000*q/$S*L (12)
Where.
Pr: Average precipitation rate of sprinkler. mm/h 360000:a constant related sprinkler’s angel. q: flow rate of sprinkler. m3/h ф: Working angel of sprinkler. 0
Precipitation rate requires considering soil infiltration rate in order to prevent runoff and deep seepage to be determined.
