Design and Installation Guide for Automatic Irrigation Systems

Through this Guide you will be able to understand the true operation of the irrigation systems, you will learn to design and build this type of equipment. The most commonly used systems (sprinklers, micro sprinklers and drip) will be discussed, including their advantages and disadvantages in different applications, and the design of sprinkler networks and pressure calculations will continue. We will also talk about the installation of an automatic control system consisting of solenoid valves and irrigation programmers.

Elements that make up the installation:

This system consists of many components assembled together, such as sprinklers, pipes, fittings, valves, cables, etc. Next, we will show the main elements that should be used and their characteristics.

What is a water spout?

The spout is what we call the element that transports the water to the plants, normally this is the irrigation system and in different types of applications there are special dispensers , such as impact sprinklers, sprinklers, micro sprinklers and droppers. Be sure to check the what the best sprinkler above ground are before you start.

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Impact nozzle

This sprinkler can be used to irrigate at a distance of 10 to 12 meters, making it suitable for watering large areas. This type of sprinkler produces a jet of water, which is rotated to cover the area to be irrigated. To adjust its angle of rotation, it has two stops, which can be adjusted to operate at different angles.

Shrub sprinklers and pop-ups

The applicable range of this sprinkler is 3.5 to 4.5 meters, which is ideal for medium-sized areas. The two sprinklers have the same type of nozzle. The difference between the two is that the bush sprinkler is installed in the pipe at a certain height, so the water flow will not be interrupted by the plants. On the other hand, the PopUp sprayer is more suitable for the lawn sprayer, as it remains hidden underground due to the action of the water pressure and only appears a few centimeters when watering.

Generally, the nozzle of this type of sprinkler is designed for a certain irrigation mode. There are nozzles, narrow strips, etc. used for irrigation of 360º, 180º, 90º. An adjustable angle nozzle is also provided, which is suitable for more complex shaped areas. Although the latter is more versatile, it is usually more refined than conventional nozzles.

Micro nozzle

This sprinkler is suitable for small areas, corners and areas with high plant density, its range is approximately 1 meter. Although they can be installed in pipes similar to bush sprinklers, it is usually more practical to insert them into black polyethylene hoses camouflaged between plants. Like bushing sprinklers, there are micro sprinklers that can spray 90º, 180º, 360º and narrow stripes.

Adjustable dripper

This type of emitter allows you to wet a small area around it and is very useful for watering tree canopies and for watering where the grower is too small to use a micro sprinkler. The flow rate of this type of dripper is adjusted by turning its upper part. However, it is recommended not to adjust them with a small flow rate because they have a tendency to block.

Self-compensating dripper

This type of transmitter produces a very small flow rate (generally 2 to 8 liters per hour), leaving a small pool underneath. Due to the small delivery flow rate, despite requiring a longer discharge time compared to other types of nozzles, a large number of drippers can still be placed in the same circuit. On the other hand, because the wet area is very small, it reduces water loss through evaporation and reduces weed growth.
These features make it a good way to water trees and shrubs in large areas like plots. In a typical transmitter, the delivered flow is highly dependent on the water pressure, which can be a problem in large and / or uneven installations. As the name suggests, the self-compensating dripper is characterized by a mechanism to compensate for this effect. Even if there may be a pressure difference, all the drippers in the device can still deliver a similar flow.

What is a valve?

They are taps that are used to activate different irrigation circuits. In the case of semi-automatic installation, a ball valve is usually used, which has a lower resistance to flow compared to other types of valves.

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How to design the sprinkler network?

When designing a sprinkler network, there may be different technically correct ways to cover an area, and none is significantly better than the other. There are different types of sprinklers with different ranges, precipitation rates, pressure requirements, and vulnerabilities. If only geometry is considered, nozzles (rotor and impact nozzle) need to be placed in a wider area, conventional nozzles need to be placed in a narrow area, and micro nozzles or drippers need to be placed in a very dense area. . However, different types of sprinklers have different pressure and flow requirements.

In this case, the sprinklers will normally operate at a pressure of 10 m.w., whereas most rotors and impact sprinklers require a pressure of 17 m.w.c. And more. Therefore, if the pressure available in the network is low, even over a large area, we should prefer conventional sprinklers. On the other hand, the flow consumed by the rotor and the impact sprinkler is similar to that of the traditional sprinkler, and the area covered is several times greater. Therefore, using an impact sprinkler will reduce the flow required to cover a specific area of ​​the garden, which can be an important advantage in installations with high pressure drops (narrow pipes and low flow meters).

Irrigation design

This feature can also use a less dense pipe network and dig fewer trenches. However, the dense network based on short-distance sprinklers allows the device to adapt to changes in the garden, such as plant growth, swimming pool construction, etc. Finally, there are differences between similar sprinklers from different manufacturers, so it is recommended to consult different manuals. In summary, the sprinkler types selected must be analyzed according to the specific situation, and the advantages, disadvantages and costs of the different options must be weighed.

How to distribute the circuit?

The following criteria must be considered: In the same circuit, the precipitation of the sprinklers must be similar and the water demand of the plants must be similar. On the other hand, you must ensure that each sprinkler head receives the required flow at the required pressure. For this reason, it is essential to estimate the flow rate that the water device can deliver under the pressure required by the type of sprinkler used. Then the sprinklers should be grouped as follows so that the water consumption of any group does not exceed the water provided by the equipment.

Can you determine the ideal pipe design step by step?

Usually no, because there is usually more than one technically feasible option. Therefore, once you know the characteristics of the starter, you must consider one or more plausible solutions, check its expected performance, cost, and see how to improve it. At this stage, it is not necessary to propose the last detailed solution. For the first approximation, it is sufficient to define some relevant variables, for example, the type of transmitter, the approximate position relative to the initial position considered, the initial recommendations for the flow of the circuit and the diameter of the pipe.

Then, the pressure losses in the circuit should be estimated, by sections, and observe if they remain within acceptable ranges. You should also look at the bottlenecks of the facility and see if its capacity can be improved at a reasonable cost. It should also be observed whether a relevant economy can be achieved by reducing the capacity of some part of the installation or by requiring more of a circuit.

Do I need to perform the same steps for each circuit?

It is not necessary. The purpose of this process is to design a circuit that can function normally at low cost. If we calculate the worst case circuits and they work, other circuits of similar design will work too. Some cost reduction possibilities may be missed; therefore, it is necessary to see if the costs involved can be analyzed in greater depth on a case-by-case basis.

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Is it a good idea to make the most of installed capacity to reduce costs?

This is generally not recommended because in most cases the water pressure cannot be guaranteed. On the other hand, in many cases, if necessary, you can leave a little space to add one or another additional sprayer. Is there a circuit that is more unfavorable than other forms of circuit? Yes, the longer the path to the last sprinkler, the greater the pressure loss. For the same reason, in a circuit with a relatively “normal” shape, the worst case is that the nozzles are aligned with the valve at one end. Next, we will look at two typical circuit boards, one of which corresponds to a row of 180º nozzles, and the other corresponds to a row of 360º nozzles.

Although choosing a diameter for these pipes is not the only possibility and is not ideal in all situations, it is a good starting point for designing a sprinkler network. It should be noted that many other forms of circuits can be considered as combinations of linear circuits or their variants.

What steps must be followed in the hydraulic design of an irrigation system?

We must first understand the characteristics of the water starter. That is, the available pressure and the pressure loss under different flow rates. This can be done by calculating the loss of each element (counters, taps and pipes) that make up the starter, or by determining the characteristic coefficients of the equipment through experiments, and then carrying water until reaching the last corner. For locations smaller than 1000 square meters, 32mm diameter pipes are usually suitable.

In larger areas, it is convenient to evaluate larger diameters. Next, determine the time consumption of the end of the mold and calculate the pressure drop for each section. If the pressure loss in the mold is moderate relative to the start-up loss, the size of the mold may be appropriate. Otherwise, changing the diameter may be reasonable. The next step is to calculate the flow that can be drawn at the pressure allowed at the end of this matrix. To do this, we consider the available pressure (normally the pressure is slightly lower than the measured pressure), and we subtract the pressure loss that occurs in the mold, elbow, solenoid valve, etc. at the beginning.

This calculation can be performed for different provisional diameters. It should be noted that for many sprinklers, there is a certain range of allowable pressure, and its range is pressure dependent. In this case, the pressure required by the sprinkler and the design circuit range must be determined at this stage. Then design the irrigation circuit itself. At this stage, determine the location of each sprinkler, as well as the preliminary design and diameter of the irrigation pipe. Finally, check the behavior of the entire system. It is important to verify that the pressure in the sprinkler is sufficient, that there are no water hammer beyond the allowable range, and that there is not a large over-investment in underutilized components.

General advice

For the main pipe, it is convenient to choose an accessible path and reduce the risk of damage. For example, paths under the lawn are generally better than paths under the ground where trees are to be planted. We must bear in mind that to intervene in a pipe (repair it or insert a tee), the ideal is to remove a section of pipe equivalent to about 100 times its diameter. Consideration should be given to modifying the system in the future.

From this perspective, it is reasonable to consider the design of circuits with additional water spray functions or the preparation of facilities to easily add new circuits. They should be handled where they are needed for use. The die with the highest diameter is beneficial to the performance of all circuits, so it is considerable to make it larger than the tube in each circuit. When the pressure is low and the available free space is small, consider what to do if the situation worsens and the installation fails.

If the solution is a pump pond, consider where to place it and how to connect it. It may be reasonable to reserve a wire to issue the start command and to lay a pipe to feed the pond. Note that this solution can be applied to irrigation or to the entire irrigation house.