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<br />Appendix A: Irrigation Glossary <br /> <br />1000/0 Coverage: The design goal of all sprinl<ler system designers. Sometimes used <br />(incorrectly) in place of the term "head to head coverage". 1 00% coverage is the objective <br />of head- to-head coverage. But head-to-head coverage does not always result in 100% <br />coverage. <br /> <br />Angle Valve: A type of valve in which water enters through the bottom inlet, turns 90 <br />degrees, and then flows out through a side outlet. (Rain bird CD-ROM: What is an <br />Irrigation System?: Components). <br /> <br />Anti-Siphon Valve: A control valve with a built-in atmospheric vacuum breaker <br />(bacl<flow preventer). Most commonly used in residential irrigation systems where code <br />allows them. Must be installed above ground. <br /> <br />Arc: The part of a circle that the sprinkler covers with water. Arc is expressed in degrees <br />i.e. a sprinkler that has an arc of 360 degrees covers a full circle; 180 degrees covers a <br />half circle. (Rain bird CD-ROM: What is an Irrigation System?: Components) <br /> <br />Atmospheric Vacuum Breaker (A VB): Least expensive type ofbacl<flow preventer. <br />One must be installed downstream from every control valve; A VB's cannot remain <br />continuously pressurized. (Rain bird CD-ROM: What is an Irrigation System?: <br />Components). <br /> <br />Backflow Preventer: A device that prevents contaminated water from being sucl<ed bacl< <br />into the water source should a reverse flow situation occur. (This happens more often <br />than you realize). In most places backflow preventers are required by law on all <br />irrigation systems. Back flow preventers are assemblies consisting of two checl< valves <br />and two shut off valves. They are generally installed on the mainline upstream from the <br />control valves. <br />(http://search.globalspec. com/ProductFinder/FindProducts? query==Checl<%20V alves) <br /> <br />Booster Pump: A device to increase the water pressure in a system where some pressure <br />already exists. For example, if water comes from a water company at 40 PSI of pressure <br />but you need 80 PSI of pressure for the irrigation system, you would use a booster pump <br />to increase the pressure. <br /> <br />Check valves: Mechanical valves that permit gases and liquids to flow in only one <br />direction, preventing process flow from reversing. They are classified as one-way <br />directional valves. Fluid flow in the desired direction opens the valve, while backflow <br />forces the valve closed. <br />(http://search.globalspec. com/ProductFinder/FindProducts? query==Check%20V alves) <br /> <br />Diaphragm: The part of the valve that controls water flow. When the diaphragm is <br />raised, the sprinl<lers in that zone emit water. When the diaphragm is lowered, the <br /> <br />14 <br />