Circuiting Emitters -II
Let's analyze this circuit and complete its design. The dashed line represents a sprinkler system sub main on the project site. From our site information, let's assume we know that we have 12 gallons per minute flow available at the end of this line at 60 psi water pressure.
Using the 15' diameter tree we have practised on in earlier examples, we also know its requirements:
1. 3 emitters per tree matches soil type & area.
2. 6 gph flow per tree matches water flow needs.
3. 4.5 hour per day (peak season) matches water requirement and time available.
If we decide to use 12mm tubing as our lateral (the line from the valve to the emitters) the emitter connection diagrams show three options for installation. In #1, a multi-outlet emitter connected to the supply tube has three distribution tubes (sometimes called spaghetti tubing) each delivering 2 gph to the properly spaced points. In #2, three 2-gph emitters are used. Two of the emitters is pushed into the main supply tube and the third is installed on the end of a tube that is tee-connected to the main tube. The last diagram (#3) shows three 2-gph emitters installed on a loop of the supply tube.
We -know the total flow of 90 gph is within the flow limit of the.580" tube so that means one tube can supply all the trees. On a scaled drawing for the project, we can measure to see if the row of trees exceeds our 300, length limit.
Assume the center of the last tree to our 1" existing main line is almost exactly 300', and is within our length specification. We are now ready to draw in the tube connecting all the trees and decide which connection method to use for the emitters.
In circuiting example number one, the designer has selected the multi-outlet emitter and drawn in the emitters and supply tube. Next he needs to calculate the pressure loss due to friction in the tubing using the chart for .580 tubing on the following the example.
Circuiting Example #1
Following the steps on the table, the designer selects the right hand chart that is for 300', laterals. Reading down the chart's left hand column he looks for 90 gph and sees his choice of flows is either 85 or 95 gph. By using 95 gph he knows he will calculate slightly higher than actual losses. This is acceptable because he knows if the higher losses he calculates will work, his slightly more efficient actual system will also.
Using 95 gph the last step is to read across to the emitter spacing and find the total lateral flow loss (including losses caused by the inlet barb on each emitter which projects down into the tube and stream of flow).
