Glossary of Irrigation Terms

An outlet valve fitted to the interior of a vertical pipe (sometimes known as a riser). The orchard valve features an opening the same size as the diameter of the pipe and an adjustable cover to enable the flow of water through the pipe to be varied. Orchard valves are similar to alfalfa valves, but deliver lower flow capacity.

A measure of the pressure at which an irrigation system actually operates. Calculated by taking the static pressure of the water at the point of connection to the water source and subtracting any pressure losses occurring through the system. The operating pressure is usually measured at the base or nozzle of the sprinklers.

The hole in a sprinkler or emitter through which water is passed into the atmosphere. The size, shape and positioning of the nozzles in an irrigation system can have a clear impact on factors such as the distance over which water is applied, the placement of the water and the efficient distribution of irrigation in general.

The name given to pollution which can’t be traced to a single clear source, such as a waste-water pipe. Non-point source pollution is generally caused by rainfall or snowmelt moving through and over the ground, picking up and carrying pollutants such as fertilizers, pesticides, bacteria, sediment and other forms of man-made pollution. The pollutants are then introduced to water sources such as rivers, lakes, ground water, wetlands and the sea.

This figure represents the difference between the pressure of water taken into the irrigation system and the pressure of water inside the pump. If the net positive suction head (NPSH) is less than that required (due to insufficient water pressure) it can cause cavitation – vapor bubbles which damage the pump.

A measure of the depth of water required by a particular landscape, once factors such as moisture stored in the soil and effective precipitation have been taken into account. The amount will be the water needed to satisfy requirements such as transpiration and evaporation while irrigating the soil.

A pump which takes water in and then pushes it through two or more impellers mounted in a single shaft. Each stage of the pump is made up of an impeller, a diffuser and return guide vanes within a single casing. As the water is fed from impeller to impeller the pressure increases.

A device placed in the soil of an area which is being irrigated. It measures the amount of water present in the soil at the root zone, and this figure can then be used to vary the amount of water being delivered through irrigation. Moisture sensors can be stationary or portable. Also known as a moisture meter. 

The difference between the amount of moisture present in the soil and the amount of water the soil is actually capable of holding, once gravitational forces have drained it. The latter is referred to as the field capacity of the soil. 

A type of centrifugal pump which combines features of axial and radial pumps. Water pressure within the pump is generated by a combination of centrifugal force and the lifting action of the pump impellers. Mixed flow pumps generate a high flow rate and high water pressure at the point of discharge.

A unique set of environmental conditions applying to a specific area. Factors which help to create a microclimate include the soil type, the wind, the sunlight available and how much shade there is. Microclimates can occur naturally or can be designed into a landscape.

The pipe used to carry water from the chosen water source (i.e. an irrigation lake or well) to the irrigation system itself. The mainline will than carry water through the irrigation system to the points of delivery. In high pressure systems the pipe will probably be made of PVC. 

Magnetic flow meters (sometimes called electromagnetic or mag meters) are a flow measurement technology used in applications where a highly accurate measurement of volumetric flow of a liquid is required. In simple terms, as liquid is moved through an induced voltage the meter can measure flow, liquid velocity and the rate of flow. They can only measure liquids that conduct electricity.

The landscape coefficient is a measure of the type and density of vegetation in a given landscape, as well as the presence of microclimates (such as areas which are shaded or exposed to wind and sun). It enables us estimate of the evapotranspiration which is likely to occur as water evaporates from the soil or through the plant surface. An accurate landscape coefficient makes it easier to plan for water loss and ensure that irrigation is neither too little nor too much.

These are generally smaller pumps that provide pressure and flow assistance in a larger pump system. They are extremely useful for handling smaller, (constant or intermittent) flows of water in a system, thus removing the need for a larger pump to constantly turn on and off. For this reason they can be an excellent cost saving feature of a system - in energy savings or maintenance cost savings for example.