Here's a general guide for the inexperienced drip-mist do-it-yourselfer. Drip Mist As the reasons to install low-flow irrigation grow every year, so does the amount of retrofitting of standard zones to low-volume ones. In some markets, retrofitting is bigger than first-time installations. Progressive irrigation designers and landscape architects are using this technology to promote resource conservation and to provide healthy, diverse landscapes while saving customers money in water, energy and maintenance. At the same time, liability concerns caused by overspray are virtually eliminated. Like any other irrigation system, the primary consideration in the installation of a low-volume irrigation system is performance. However, appearance, vandalism, and accident prevention are also significant considerations. A low-volume irrigation system is similar in its basic layout to any other irrigation system. It consists of a main supply, a control zone, and a lateral/water delivery system. The main supply consists of the pipe network from the point of connection to the control zone. Depending on the requirements of the local municipality, it may also include a water meter, backflow preventer, and isolation valves. Basic hydraulic principles apply to the size and installation of the pipe network. The Control Zone The control zone consists of flow and pressure reduction devices and electric or hydraulic valves, which can include pressure and flow control devices. It can also includes filters. The technology used to apply small volumes of water involves relatively small emitters, and in some cases, small delivery tubing. Due to their size, they are more likely to clog with debris, minerals, or organic buildup. Filtration and periodic flushing can remove contaminants before they interrupt or reduce flow. Generally, a 150-200 mesh wye strainer is adequate for municipal water sources. Filters and screens should be matched to the required flow. The higher the mesh of the screen, the smaller the openings are, meaning less water will flow through the screen at any given pressure and time. Filters can be installed at the point of connection, at the control zone or at the emission device. However, the largest potential source of contamination in a municipal water system would normally be due to a break in a main or sub-main supply line. If a filter were placed before the break, the entire system would be compromised. Likewise, if the filters were placed at the emission device, each one would have to be cleaned and/or changed following an upstream break. It is recommended that a single filter be installed at the control zone. This filter should be sized for the highest flow rate among all the zones downstream of the filter. Filters should always be accessible for cleaning and flushing. The Drip Mist filter is arguably the most important factor in success. In addition to considering the flow rates through the piping and tubing, flow through the control valve is important. Size your low-volume control zone valves according to the flow they will handle and not the size of the pipe. Oversized valves can close too slowly or not at all. Check the minimum flow rate of a valve before you install it in a low-volume irrigation system. Many low-volume devices operate at pressures ranging from 10 to 50 psi. Pressure regulation should be used to reduce stress to the systems, keep emission devices from blowing apart, and maintain flow rates within specified limits for pressure-compensated devices. Some drip products include pressure regulation as part of the emission device. Others offer complete low-volume automatic valve assemblies including filtration for quick and simple installation. When assembling valve manifolds, filters, and other threaded PVC drip components, use teflon tape wrapped clockwise around all threaded fittings. Do not overtighten. The control zone should be buried in a valve box. Locate the valves where they are convenient to the water supply, future access for maintenance and in reasonable proximity to the controller for running the control wire. The valve box should be buried flush to grade with a layer of gravel at the bottom for drainage. Install the controller in a sheltered, secure location. Connect the control wire from the controller to the hot and common wires on the valve solenoid. The Delivery or Distribution System Whether laying drip irrigation in a grid or pinpointing watering areas, flow rates from the emission devices must be compatible with the needs of the plant material and the characteristics of the soil. By designing a drip system that irrigates the entire planting area uniformly you might increase maintenance (weed control), however you eliminate the risk of missing your watering targets or placing too much water in a limited part of a plant's root system. If watering the entire soil profile, space the drip tubing to provide adequate coverage uniformity. The tighter or heavier the soil, the farther apart the emitters and the laterals can be buried because the capillary activity of the soil is greater than sandy soils. For sandy soils, laterals should be spaced 8 to 12 inches apart with emitters every 12 inches on center. For heavy, clay soils, laterals can be installed up to 24 inches apart with emitters every 20 inches on center. Chart the layout according to the intended landscape, before you begin installation. Make sure to place the emitters for the future growth of the plants. Don't place them right at the base of plants or you will encourage root rot. Avoid perfectly straight runs of tubing. Instead snake the tubing around plants. For any significantly large areas you might need to install gate valves to bypass sections of the system, or to create separate control zones according to the availability of pressure and flow. Provisions should be made for flushing every lateral. The easier it is to flush the line, the more likely that the task will be done. A valve, or a fitting with an unscrewing cap, is usually recommended. Looping the lateral within a control zone makes it easier to flush. If the lateral is not looped, install a ball valve at the end of the run for flushing. The drip or low-volume lateral lines can be either rigid PVC, flexible PVC or polyethylene. They can be either buried or installed on the surface. For aesthetic and vandalism reasons, lines should be buried where economically feasible. On steep slopes, where it would be difficult to trench, the lines could be placed on the surface, but they should staked sufficiently. Even on relatively level areas, loosely staking the laterals is recommended to allow for expansion and contraction. Rigid PVC can deteriorate rapidly when exposed to direct sunlight. Therefore, when it is used on the surface, the PVC pipe should contain an agent that protects the pipe from damage by ultraviolet radiation. Whether buried or placed on the surface, snake the lateral to account for expansion or contraction caused by changes in temperature. In areas of high cultural activity (shoveling) or heavy foot traffic, bury the lateral lines about 12 inches deep and place them in a sleeve of rigid PVC pipe. Keep in mind that when laterals are buried and their water discharge points are below the surface, plant roots, weeds and mud slurry can enter the system and hurt performance. Tubing with integrated emitters and automatic flushing is available for applications where burial of emitters is required. Install at least two emitters per plant to place water on both sides for more stable and uniform root growth. Use products designed for landscape applications, not agricultural applications. Where possible, use 1 GPH or greater emitters and reduce runtimes. Emitters with extremely low flow rates are more likely to become clogged or contaminated. Following installation of laterals and emitters, flush the system and then cap it off. Let the system operate for a week or two before covering the area with mulch. Observe the wetting pattern on the soil and note any problems with uniformity or distribution. Adjustments should be made before the area is mulched. Careful installation, regular inspection of the emitters and maintenance of the filter will preserve the integrity of the system and the life of the irrigated plant material. The landscape will thrive, you will be satisfied and you will have demonstrated the efficiency and versatility of your irrigation design and installation skills. |
