How To Use An Air Compressor To Blow Out Sprinkler Lines

If you purchase a house with a sprinkler system and weren't informed that you needed to winterize the system. When you saw the neighbour outside working on his sprinkler, that you realized that they needed fall maintenance.

It makes sense. If it gets below freezing, those lines would be the first ones to freeze. Getting all of the water out of those lines is a key part of the fall season.

Here is a quick discussion on how to winterize your sprinkler system. If the steps seem too overwhelming, you can always hire a local company to come out and handle it for you. Doing it yourself should save $50 to $250, depending on the size of your sprinkler system and the area you live in.


Why You Need An Air Compressor To Blow Out Sprinkler Lines

If you have an RV, you might be familiar with using an air compressor to blow out the lines. This is similar, but the difference is that with an RV you can run antifreeze into the lines so that even if you don't get them fully blown out, you can still protect your lines. Sprinkler systems really shouldn't have antifreeze put into them as it would be damaging to the environment.

You don't want to procrastinate on this task. The underground system is likely to survive the first few freezes of the year, but the above-ground pipes -- such as the piping to the backflow preventer -- can be damaged in a single freeze.

How Big Of An Air Compressor Do You Need?

Most towns have a tool rental place that will rent you a compressor along with 50-100 feet of hose. Make sure that the hose you get has a quick-connect adapter on it. Most of them do, and it is essential for connecting to the sprinkler line.

You'll want a larger compressor for this task. Depending on the size of the compressor, you may need to rent a trailer with which to haul it. Make sure that you are getting a compressor with a standard 120-volt plug, as some of the larger compressors require 220 volts of power.

In calculating the size of the compressor you will need, you can take the Gallons per minute that your sprinkler is designed to output, and divide that by 7.5. This calculation will convert the Gallons Per Minute over to Cubic Feet Per Minute, or CFM. 

For the easiest blowout, it is recommended that you get a compressor that can do at least 25 CFM.  However, these compressors are typically 60-gallons and require 220 volts of power. So you will likely be working with a smaller compressor that can do at least 10 CFM.

If you have a flexible, black polystyrene system, you can get by with using 50 PSI. This lower PSI setting (which you adjust using the sizeable black regulator knob on the front of your compressor), allows you to enjoy a higher CFM.

For PVC systems, you'll likely want to adjust it to about 70 PSI, while still flowing about 10 CFM.

If this is a task that you expect to do frequently, you might consider purchasing something like an 8 gallon or 20-gallon air compressor that can handle the large air volume that you need. Your compressor may pay for itself in just 2 to 3 seasons of use, depending on how much it costs to hire a company to do the work. Your local hardware store or online blogs like ToolTally have calculators to help you find a unit that can deliver 10 CFM or more.

4 Steps To Blowing Out Your Sprinkler

  • Turn off the water supply. Typically there is a shutoff valve that is dedicated to turning off the water supply to the sprinklers.
  • Close The Backflow Preventer. The first step is to close the valves on either side of the backflow preventer. It's normally pretty obvious which valve you need to close as they are obviously placed near where the water flow enters the system.
  • Connect The Compressor.  There should be a blowout valve near the backflow preventer.  If you have a more extensive system, it is likely that you will need to be more careful when blowing out the lines and work through them zone-by-zone. If it is a small system and you have a large air compressor, you can easily connect it once and blow out all the lines. If you have a bigger sprinkler system, you will need to blow out each zone individually using the timer.
  • Using the Timer, Blow one zone out at a time. Set the timer to activate the first zone, connect your compressor and blow it out, and then move forward to the next. Don’t overblow the line. Stop as soon as the water stops. Overblowing the line can damage the system.

Blowing Zone By Zone With A Smaller Compressor

If you are forced to winterize your sprinkler with a smaller compressor, you will need to cycle through each zone. Connect the compressor, and then use the timer for cycling through the zones one at a time.

When the zone activates, the heads should pop out and release the water in the lines. Disconnect the hose as soon as the water stops. It is possible to quickly overheat the gears in the sprinkler heads by just running air through them.

Move on to the next zone, reconnect the hose and blow that zone out.

If you wish, you can give it a second pass. There should be very little water in the zones on the second pass, and a brief spurt of air should satisfy you that the lines are dry.

Abigail Jones

Hi, I'm Abigail. I like spending time tearing my house apart and putting it together back again. Join me on home improvement tutorials, tips on my blog.

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