Archived - Drip Irrigation for the Yard and Garden

1. Control valves. (See Figure 2.) Valves are often set up to be opened and closed automatically by a timer or other irrigation control device. Hose-end timers (Figure 3) combine a timer and a battery-operated automatic valve in one device. They are manufactured by many different companies and offer a practical alternative for simple irrigation systems that are typical of smaller yards and gardens. Figure 2. An example of a solenoid control valve.
2. Backflow preventer or anti-siphon device. (See Figure 4.) This device is required to protect the integrity of the water supply. They are required by law in many municipalities and are always a good idea to prevent contaminated water from reentering the domestic water system after the water has been shut off. They can be simply mounted at the spigot (Figure 5). Figure 3. An example of a battery-operated hose-end timer.
3. Pressure regulators. (See Figure 6.) These are required if your water source produces pressures that are higher than what the drip system components are rated for. Excessive pressure may cause components to come apart, leak, or not function correctly. Pressure regulators will reduce the pressure to what is specified by the regulator.
4. Filter system. Plugging is the biggest problem of drip irrigation. To combat this, good filtration is an absolute necessity. In fact, the filtration system should be considered the most important part of the whole system. Most home drip systems use a simple screen filter (Figure 7) to remove small particles of debris from the water. The maximum opening size of the screen should be smaller than the size of the drip emitter’s orifice. These screen filters need to be cleaned out periodically, either manually or through some sort of back-flush system. Greater volume water users will want to consider sand-media filters, disk filters, separators, or a combination of these.
5. Air- and vacuum-release valves. (See Figures 8 and 9.) These allow air to escape the system as it fills with water, and allow air back into the system after the water is turned off. These should be placed at the highest elevation points and/or at the end of long runs in the system (places where air would accumulate as the system fills with water).
6. Mainline, submains, and lateral lines. Depending on the complexity of the drip system, there may be a mainline and sub-mains (Figure 10) that distribute water to the heads of the laterals. Laterals carry the water to the individual emitters where the water is applied to plant root zones. Most mainlines are made of PVC, while submains and the laterals are most often made from polyethylene. Drip laterals can be buried in the soil or covered by mulch. This will help to protect the laterals from sun, insect, and traffic damage. The only draw-back in covering the laterals is that it then may be difficult to find and fix problems such as plugged emitters.
7. Emitters. There are many different types of emitters that operate on different principles and are made by a wide number of manufacturers. The two most common types are orifice emitters and turbulent flow emitters.
   
   Orifice emitters (Figure 11) are simply a small hole that the water flows through. Although these are the least expensive, they are the most prone to plugging since the flow rate is determined by the size of the orifice, and this must be small to create the slow dripping action required.
   
   Turbulent-flow emitters (Figure 12) force the water through a tortuous path before it is released out to atmospheric pressure. Because all of the pressure is dissipated through friction as it travels through the labyrinth inside the emitter, larger diameter passageways can be used and they are less prone to plugging.
   
   Emitters are typically rated in units of gallons per hour (gph) with 0.2 to 4 gph being typical. If there are large pressure differences along the drip line due to very long laterals, or if the drip lines go up and down steep slopes, then pressure-compensating emitters are available that help ensure the same amount of water comes out of each emitter regardless of the pressure at that point in the line.
8. Flush mechanism or port. To help combat plugging, it is a good idea to have a way to open up the end of each drip lateral to periodically flush out any particles in the system (Figures 13 and 14). This should be done before use in the spring and then periodically throughout the season as required.

Drip System Design

Drip systems can essentially be grouped into two categories: line-source and point-source systems. A line-source system has drip emitters spaced at regular intervals along the line (Figure 15). Water can be considered to be coming from the line as if it were one continuous source instead of a series of drippers. Drip tubing with pre-installed emitters, drip tape, and soaker hoses can all be considered line-source. Point-source systems consist of individual emitters that are placed so that water is emitted precisely in discrete locations such as right at the base of a plant (Figure 11), or into a single pot (Figure 16).

Line-source systems are a good option for lawns and gardens while point-source systems fit better with irregularly shaped flower beds, potted plants, and individual, isolated plants.

The limited movement of water from a dripper can be both a negative and a positive thing. It is negative in that not a very large area is irrigated, but can be positive in that water can be closely controlled to leave certain areas in a garden dry. This means that fewer weeds will germinate and grow in areas that are not meant to grow plants, such as garden pathways or areas between plants.