Control Components

The next step is to design the control portion or head of the circuit. The control head of a drip irrigation circuit usually consists of three components: the valve, the pressure regulator and the filter.

The valve, either manual or automatic (electric) turns the water on and off and must be able to operate at the low flow required. The pressure regulator controls the inlet pressure for the lateral tube to meet the requirement previously calculated.

The filter screens the incoming water to prevent particles large enough to clog the emitter from passing into the tube. The filter's mesh count needs to be equal to or slightly above the emitter's filtration requirement.

The control equipment will also create flow losses as water passes through them. The equipment catalog from which you select your control components should state the flow range they can handle and the flow loss through them at given gallons per hour or gallons per minute within that range.

In this case our pressure after the control components equals or exceeds the pressure requirement at the tube entrance. If a fixed regulator is not high enough in outlet pressure (generally they are available in 15, 20 and 25 psi models) an adjustable regulator can be specified and set at the desirable pressure.

In cases where the supply pressure is very low you may not need a regulator in your control components. With pressure compensating emitters that maintain a fairly constant flow rate even at higher pressures, you day also p ibl get away without a regulator.

In the future you will see entire control heads using the pressure calculation below, let's calculate control component losses for a 90 gph flow.

20.000 psi for the emitter
2.164 psi flow and barb loss
2.165 psi elevation loss
24.329 psi needed at tube entrance

If the designer chose an electric valve that loses 1.5 psi at 90 gph and a filter that creates a loss of .5 psi at 90 gph and we have 60 psi in the sub main to our valve, we would have:
+ 60 psi
- 1.5 valve loss
- .5 filter loss
+ 58 psi at the inlet of the last control component, the regulator.

At 58 psi on the chart of a typical fixed pressure regulator (the 25 psi outlet model) the outlet psi may read 26.3 psi for 90 gph flow. Without the expense of an adjustable regulator the designer now knows he will meet his 24.3psi pressure requirement and 90 gph flow requirement for the circuit.

(Assemblies of control components) cataloged as single units with inlet and outlet pressures rated at various flows.The entire proceeding design system can be used to greatly shorten the time necessary for drip system planning. To further speed up the above process, design and calculate your largest circuits first, and of those, check to see if the furthest circuits from the water source have sufficient pressure and flow.

Designing these "worst case" circuits first quite often will tell you what size circuits, control heads, and regulator pressures will work on all the smaller circuits

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