3.1 General Components

Irrigation systems consist of pipes that are used to transport water and nutrients. Other components are needed to complete the system. The following discussion will familiarize the reader with many irrigation components and their purposes.

Pumps move the water (gallons per minute) and bring it under pressure (pounds per square inch, psi).

Water meters measure how much water has passed a given point in the system.

Backflow preventers stop water from flowing back to the source and carrying contamination back to the source, i.e. a well. Backflow preventers often have a check valve, air vacuum breaker, and low pressure drain as its' components.

A check valve is a one-way flow device that allows water to pass in one direction but that closes if water reverses direction. The valve has a gate inside that swings open in one direction but is pushed closed by water flowing in the other direction.

An air vacuum breaker allows air to enter the pipeline when there is no water pressure and thus prevents a vacuum from being created to pull water pass a closed check valve. It also allows air to escape when a water pipeline is being filled with water. A ball is used to close the opening when the water rises to fill the device.

A low-pressure drain valve opens when the system pressure is very low to allow water to drain out. It is used to drain any remaining water in a pipeline after the system is stopped or to drain any leakage past a check valve.

Valves are used to turn on or off the flow of water in the pipeline. Manual valves are typically gate or ball valves that open fully to allow water to pass with a minimum of restriction. A gate valve has a mechanical gate that is opened or closed by turning the knob or handle. A ball valve uses a ball with a hole in it; the handle is turned so the hole is in the direction of flow to allow water to pass. Electric solenoid valves use 24-volt electric to hold an internal valve open; a time clock controller is used to operate the valve.

Filters are used in microirrigation irrigation systems to prevent small particles of dirt or organic debris from clogging the small orifices or outlets in the emitter devices.

The emitters are engineered devices that control the water flow at some pressure. Some emitter devices are pressure compensating which means a diaphragm moves with the pressure to adjust water flow with pressure changes, so the water discharge is fairly uniform over a range of pressures.

Fertilizer injection systems deliver dissolved or liquid fertilizer into the irrigation system when the water is flowing. Sometimes other chemicals are injected to control other water quality situations. A concentrated fertilizer solution is prepared for injection through the fertilizer injectors. The injectors mix the concentrated fertilizer solution into the irrigation water in some ratio, i.e. 1:200, to dilute the final solution to a calculated parts per million (ppm) of nutrient, such as 200 ppm Nitrogen. The concentrated solution would be 40,000 ppm N in this case.

Electrical conductivity (EC) and pH meters may be desired beyond the injection site to monitor the nutrient levels in the irrigation water. Some of these pH and EC meters are designed to be housed in the main water pipe (in a greenhouse or hydponic setting), so that continuous monitoring of TSS and pH can be logged by a computer.

Pressure regulators act on moving water to maintain a given pressure beyond the device. They can be preset to specific pressures or adjustable to a range of pressures. Pressures vary through the system and the regulator can help to provide irrigation zones with the proper operating pressure.

Pressure relief valves are designed to allow water to "blow off" to reduce pressure when sudden increases in pressure occur within the system. Water hammer is a term that refers to a sudden increase in pressure due to a valve being closed too quickly on fast flowing water downstream. Water hammer can cause pipes and valves to burst so it is avoided with proper design.

Many of these components are sized by the allowed flow rate through or past the device. The diameter size does not necessarily relate to the pipeline size. The pipeline is sized for the flow rate and distance the water is being carried so the pressure loss by friction is not excessive.