In order to achieve a maximum efficiency of your drip irrigation system, it is essential not only to know what type of water you use (water quality), and therefore to understand the right filtering system, but it is also necessary to know the peculiarities of water to optimally build your micro-irrigation system. Therefore, it is necessary to define the water amount in the system, as this value is fundamental for its design and for the definition of its costs. The quantity of water is expressed according to two fundamental parameters:

• Pressure;
• Flow rate

 Water pressure

General definition of pressure: pressure is a unit of measurement that measures the action of the force exerted on a surface compared to the unit of surface on which it is exerted. Simplifying the general definition, water pressure is the force exerted by water on a surface. It is measured either in atmospheres or in bars.

There are two classifications of water pressure:

Static pressure is a measure of water pressure when the water is still. In other words, the water does not move inside the irrigation system. To measure it, you need a pressure gauge to be connected to a valve by a simple rubber pipe.

Dynamic pressure is a pressure measure when water is moving (also known as “working pressure”). It is obtained by measuring the pressure by delivering a certain flow rate.

It is necessary to repeat a series of measurements at increasing flow rates to obtain a performance curve of our system.

To guarantee a correct design you should take into account the dynamic pressure – from pump, from gravity etc. – when the system is at its maximum absorption!

Flow rate

General definition of flow rate: flow rate is the amount of substance that crosses a section of area A in a unit of time.

Trying to simplify this general definition, water flow rate is the amount of water that an available water source can guarantee to the crops basing on their needs. It is measured in liters per minute or in cubic meters per hour.

The flow rate is one of the most important factors while designing your irrigation system. When you know the amount of water that your system absorbs in relation to the available water source, you will be able to understand if it is necessary to divide the irrigation system into several areas or what diameter of the mainline pipe to choose.

There is no ideal flow rate or pressure value, so there is also no a universal value that is suitable for different micro-irrigation systems. Nevertheless, it is important to underline how the parameters can vary according to the system characteristics, that is basing on the area extension and on the type of irrigators you want to use.For example, a flow rate sufficient to irrigate a 100 m2 garden will be absolutely inadequate to irrigate a 1000 m2 garden.The preliminary phase of measurement both of the flow and the pressure of water is therefore essential to define the design of an efficient and suitable irrigation system.

Table [1] below can support you during the design of your irrigation system. It highlights the flow rate of a mainline pipe from rigid PE or from flexible PE (e.g. Rioflex) at 1 bar of pressure, at standard roughness conditions and without critical conditions such as bends, bumps or other obstacles.

[1] – This table has been obtained by using hazen-williams formula and the formula of cao, assuming a section of the pipe on which a pressure (working) of 1 bar is exercised, which is the operating pressure of the mainline pipe at the points where derivations start.

In order to calculate the thrust required by the delivery pump, it is necessary to calculate pressure losses, section length, slopes etc.