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www.landscapeirrigation.com Landscape and Irrigation October 2015 27 Use an air compressor with an airflow rating of 80 to 100 cubic feet per minute (CFM), for mainlines that are two inches or less. (Larger systems will require larger air volumes.) When operating the air compressor, the lower the pressure the better. Don't exceed the maximum operating pressure of the heads for each zone, and never exceed 50 psi for polyethylene tubing and 80 psi for PVC pipe. Why? Irrigation components such as rotors are designed for the resistance that water provides. Once the water evacuates during a blowout, compressible air strikes the impellers and gears; if the pressure is too high, the change in velocity can be almost explosive. Larger tow-behind compressors often lack the regulators needed to bring pressures down this low, so make sure you have one available, especially if a rental yard compressor is used, to ensure your pressure stays within reasonable limits. 4. USE AN APPROPRIATE CONNECTION POINT. Whenever possible, avoid blowing air through water meters, flow meters, pumps and backflow preventers. These devices are designed to handle water — high-velocity air can spin and disturb components in ways they were not designed to handle, resulting in repairs, replacements or voided warranties. For an optimal air hose connection for small to medium size systems, use a quick coupler valve (QCV) downstream from the backflow device, if one exists. If a QCV is not available after the backflow, consider installing one just for this purpose. A quick connect adaptor for a 1-inch air hose plumbed to a key and swivel makes for a clean connection. Some models of backflow preventers also have a check/relief valve assembly that can be removed and replaced with a blowout fitting to allow for blowout without component damage. If there are any manual drain valves on the system, make sure they are closed before the blowout and close the backflow isolation valve. Because air-relief valves relieve air, they also need to be removed and capped so air pressure can build in the system during blowout. 5. KEEP IT COOL. When using an air compressor, air can compress when the flow of water and air is restricted. The more air compresses, the hotter it gets — hot enough to warp and even melt some components! Keep pressure and temps down by preventing "dead-heads" (no-flow situations) against closed valves by using lower pressure and keeping a flow going at all times. During the blowout process, gradually open the compressor valve after you energize the first valve. Using a handheld remote or while standing at the controller, cycle through each zone, from the farthest to closest. Keep at least one valve open while compressed air enters the system, and turn off your air compressor before closing the last valve. Cycle through the zones two or three times, until they run dry (typically 2 to 3 minutes). To avoid overheating the system, run air for no more than about two minutes per pass through each zone, and stop once the zone is dry. Refer to manufacturer's recommendations for blowing out and/or draining drip components. 6. BE THOROUGH. It's important to know the system, and make sure each component gets drained — a system reference diagram can really help. After the blowout, drain any riser pipe before and after the backflow device. Many facilities remove above-ground units and store them inside, capping the risers once drained. Refer to the manufacturer's recommendations for draining or removing your backflow device. Typically for a pressure vacuum breaker (PVB), double check (DCV) or reduced pressure principle device (RP) you'll need to open the test cocks a quarter turn and open ball valves 45 degrees for the winter. If these devices must remain pressurized, blankets, heat tape and heated enclosures are available. For pumps, turn off the power and empty all water out of drain ports. Add any lubrication or other maintenance necessary by referring to manufacturer's recommendations. If you've manually or automatically drained the system, make sure any sprinklers with check valves have also been pulled up and drained. And be sure to seal off any open points in the system. Finally, adding silica gel desiccant packs inside any controllers housed outdoors can help prevent condensed water and ice from causing damage. Power can be left on to the transformer, but make sure to choose the "off " or "rain" setting for the controller. Tom Glazener is employee development and training coordinator, and Laura Ory is social media & digital strategist at Ewing Irrigation and Landscape Supply. SPECIAL SECTION LI PHOTOS ON THIS PAGE BY JESSE TALLMAN, EWING IRRIGATION