How Do You Use a Towable Air Compressor to Winterize an Irrigation or Sprinkler System? (Hint: Read this Article)

Portable compressors can find work in so many sectors. It’s what makes them attractive for rental houses. They can end up supplying air to pneumatic tools like breakers and sandblasters on a construction site or find employment in the entertainment industry, inflating kid-packed bouncy houses. Here’s another cool compressor application — winterizing irrigation systems. It’s a sure sign that winter’s coming when some guy shows up at your house with a compressor to blow out your lawn’s irrigation system.

Landscape contractors and irrigation companies can spend a huge chunk of their fall season (usually a six-week period from October 1 to mid-November) winterizing thousands of single and multizone sprinkler systems just using a compact, portable air compressor. It’s more than just homes. Golf courses. Business parks. Regular parks.

“The size of the job at hand helps determine what size portable diesel air compressor is suitable,” explains Navendu Sharma, senior product manager with Sullair, a global compressor manufacturer and supplier for all types and sizes of compressors. “The Sullair 185 Series, a 185-cfm at 100-psi portable air compressor, is most commonly used for winterizing irrigation systems at residential, single family homes or at small commercial sites. With a light and compact design, it’s also a fuel-efficient solution. In slightly larger jobs, such as commercial properties, an air compressor that can handle 375 to 425 cfm at 150 to 200 psi is often used. With large areas, such as golf courses, lawn care companies often use big air, like our 1,600-cfm at 150-psi Sullair 1600H, to cover the large area.”

Blow by Blow

Winter can be hard on pipes. For sprinkler and irrigation infrastructure, water can remain in low spots or voids in the system (don’t trust those manual or automatic drain valves), and winterizing or blowing out the irrigation system with pressurized air is the best way to know that the pipes will be protected from freezing water, cracking and the damage that cold brings. Although larger compressors can be used for bigger projects, an air compressor that provides 80 to 100 cu ft per minute (cfm) is pretty ideal for a lot of residential and commercial sprinkler winter work. It’s also easily towed to a jobsite with a pickup truck. While that size is ideal, the air power will still need to be regulated down.

“The most important thing contractors need to be aware of is these pipes cannot sustain more than 40 to 60 psi,” says Sharma. “So, when using a portable air compressor that puts out more than 40 to 60 psi, lawn care contractors need to use a pressure reducing valve [or pressure regulator] so as not to destroy the piping. This means when lawn care contractors use a larger machine, such as a Sullair 185 which produces 100 psi, they need to regulate the pressure coming out so as not to damage the system.”

Whether it’s a quaint residential lot or a large commercial golf course, the first step in winterizing an irrigation system is always the same — turn off the water. The irrigation line, which is separate from the potable water line, is directed from the basement or crawl space of a home, a utility space or in the service station at a commercial facility. Find the line valve and close the connection. Once the water and pressure have been bled from the system, it’s time to connect the air compressor to the drain valve.

Contractors usually hook the compressor to the drain valve downstream from the backflow device or preventer, required by water departments to separate water from the irrigation system and indoor water supply. Typically, a standard garden-hose-sized air line of 3/4 in. is suitable for residential and small commercial winterizing jobs. With the compressor valve in the closed position, attach the hose to the fitting.

“Most systems will have a hose bib-style connection although some may have quick-couplers,” says Cody Blythe, product specialist for air compressors at Doosan Portable Power, which has a global portfolio of air compressors, mobile gen sets, light towers and beyond. “It’s best to have a couple different options on the truck just to be certain you have the correct fittings to safely connect to the mainline.”

The installation process always starts the same way — PPE like gloves, ear protection and ANSI-approved safety eye wear. Then…

“Make sure the compressor’s discharge valve is closed and start/load the compressor,” says Blythe. “Close the backflow valve and turn on the zone valve that is furthest away from the compressor. Slowly open the compressor’s discharge valve to begin blowout. Do this for each zone from farthest to closest to the compressor until each zone shows no signs of water exiting the irrigation heads.”

As Blythe mentions, a popular practice is to start with the zone furthest from the compressor and highest in elevation and work your way back, but we’ve also heard that it’s wise to just start with the station called “zone one” to ensure all zones get winterized. Most modern systems will have a controller that will let you cycle manually through each zone. Some older systems or residential systems may have manual valves to turn on and off for each zone. In either of the systems, valves will be located throughout the yard.

“To minimize the risk of bursting a pipe or fitting in the system you should never have the compressor running without at least one of the zones or valves in the system open,” says Blythe. “The goal is to push the air through the pipes, not to pressurize them.”

All of these pipes and nozzles will have pressure ratings. Typically, 80 psi is the maximum pressure rating for rigid PVC pipe, and it’s 50 psi for polyethylene pipe. Adjust the pressure regulator on the portable air compressor accordingly. Also…

The Dangers of Heat

The job is completed when the sprinkler heads are not spouting any water (or a water vapor or fine mist instead of water). After each zone has been blown, try hitting each zone again with about five seconds or less of pressurized air — just to make sure any voids or low spots in the pipe get completely flushed. Once the job is finished, disconnect the air compressor and release any air pressure that may be left. The backflow device or pump should also be drained afterward (techniques vary for each type). Just remember: Do not blow the system out through the backflow or pump. First, blow out the system, and then drain the backflow or pump. Compressed air can easily burn the rubber seals inside the backflow device.

In fact, compressed air can create a lot of heat. For example, running a compressor for too long can cause friction, melting pipe. Each zone should only take about two to three minutes per section. It’s better to use two or three short cycles per zone than to have one long cycle to reduce heat. Compressors can also emit heat near the physical unit.

“Dry leaves can increase the risk of a fire,” says Sharma. “With many dry leaves laying around, be sure to follow local and regional regulations regarding operating diesel-powered equipment. Make sure engine exhaust is not directed toward a pile of dry leaves. If it is, use a spark arrestor on the exhaust to catch any potential sparks. Fortunately, Sullair 185 and 375 portable compressors emit exhaust through the top of the canopy to avoid this, but not all portable compressor manufacturers do.”

Keith Gribbins is publisher of Compact Equipment.

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