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<br />Polyvinylchloride (PVC) pipes: Usually white or gray and semi-rigid. Most PVC pipes <br />are connected using PVC fittings that are glued on. PVC pipe is rated in by the pipe's <br />width and the pipe's operating pressure. (Rain bird CD-ROM: What is an Irrigation <br />System?: Components). <br /> <br />Pop-Up Sprinkler Head: A sprinl<ler head that retracts below ground level when it is not <br />operating. Both sprays and rotors are available in pop-up heads. <br /> <br />Precipitation Rate: A measurement of water application. The measurement is given in <br />the depth of water applied to the soil. In other words the depth that the water would be if <br />it didn't run-off or soal< into the soil. In the USA precipitation rate is measured in inches <br />per hour. In metric countries it is measured in millimeters per hour. <br /> <br />Pressure Gauge: A device used to measure water pressure. The best pressure gauges are <br />"liquid filled", however most cheap gauges worl< well enough for irrigation use. If you do <br />use a cheap gauge, don't leave it connected to the water pipe. The constant pressure will <br />ruin it. <br /> <br />Pressure Reducing Valves: Provide a steady pressure into a system that operates at a <br />lower pressure than the supply system. A reducing valve can normally be set for any <br />desired downstream pressure within the design limits of the valve. Once the valve is set, <br />the reduced pressure will be maintained regardless of changes in supply pressure (as <br />long as the supply pressure is at least as high as the reduced pressure desired). <br />(http://www.tpub.com/content/engine/14105/css/14105_96.htm) <br /> <br />Pressurized Vacuum Breaker (PVB): Similar to an A VB, but only one needs to be <br />installed on the irrigation main; it can remain constantly pressurized. (Rain bird CD- <br />ROM: What is an Irrigation System?: Components). <br /> <br />PSI: Pounds per square inch <br /> <br />Radius Adjustment Screw: Allows the radius of a head to be reduced by up to 25 %. (If <br />reduced more than 25% an irregular water pattern will result) The radius adjustment <br />screw on a spray head can be turned with a flat blade screwdriver. Turning the screw to <br />the right reduces the throw radius while turning the screw to the left yields the maximum <br />throw radius <br /> <br />Radius of Throw: The distance a sprinkler throws water. (Rain bird CD-ROM, What is <br />an Irrigation System?: Irrigation Components). <br /> <br />Reduced Pressure Backflow Preventer: A very effective type of back flow preventer <br />that is used for commercial and high-hazard sites. (Rain bird CD-ROM: What is an <br />Irrigation System?: Components). <br /> <br />Riser: The connection between a sprinl<ler or other irrigation device and the pipe that <br />supplies the water to it <br /> <br />18 <br />