How to Winterize a Landscape Sprinkler System

Using a compressor to blow water out of the sprinkler system.

Annually before the first freeze occurs, it’s important to go through an irrigation blowout. This is a priority for any homes where the frost level extends below the depth of installed irrigation piping. If you live in the south and your irrigation pipes are below frost level, you will not be equipped for this procedure, but will need to winterize your Plumbing Vacuum Breaker. Click here for that article.

Even though you may have already drained the water out of the irrigation system itself, some water may remain and can freeze, expand and crack piping. In many freezing climates, polyethylene pipe, a flexible, black pipe is used. Although this pipe is flexible, it can expand under pressure if water is left inside which can rupture the walls of the pipe. Freezing water in the backflow assembly portion of the system can damage the internal components and crack the brass body entirely.

In order to minimize the risk of this type of freeze damage, winterization of the irrigation system must occur. In places where this process is mandatory, irrigation systems are installed with three different types of water removal: auto drain, manual drain or blowout. If you don’t know which type your system uses, it is best to use the blowout method for the least risk.

This how-to guide will help you learn all of the steps involved in winterizing your sprinkler system in a cold climate. We will look at two different ways to remove water from your pipes and sprinklers, one using the blowout method (the best to use if you don’t how your system drains water), the other using drain valves.

Manual Drain Method

To use the manual drain method, shut off the irrigation water supply. Next, open all of the manual drain valves. Once all of the water has been drained from the mainline, open the boiler drain valve or the drain cap itself and the waste valve. Drain all of the remaining water between the irrigation water shut off valve as well as the backflow device. Next open the test cocks on the backflow device itself. If your sprinklers have check valves, pull up on the sprinklers to allow the water to drain out of the bottom of the body of the sprinkler piece. Depending where the drain valves are located, there could be a little water left over in the piping, sprinklers or the backflow. When all of the water has been drained, close all of the manual drain valves.
 

Automatic Drain

Use this method when your automatic drain valves are located at the low points and the end of the irrigation piping. These will automatically open and close and drain water when needed (usually when the pressure in the piping is less than 10 PSI). To activate this method, shut off all of the irrigation water supply (the shutoff typically will be found in the basement). Activate the station to relieve the system pressure.
 
Once you are certain that the water has drained out of the mainline entirely, open the drain cap or the boiler drain valve on the stop and waste valve. Drain the remaining water (typically there is some between the backflow device and the irrigation water shut off valve). Next, open the test cocks on the backflow device. If your sprinkler system has check valve, you will need to pull up on the sprinklers to allow the rest of the water to drain out of the bottom.
Depending on where you live, you may want a combination of both the auto drain system and the manual drain for the mainline.
 

Blow Out Method

It’s important that you wear ANSI-approved safety eye protection when doing this option. Always take care when you’re blowing out an irrigation system with compressed air. Also, flow sensors can be damaged from this technique and should be removed before injecting any compressed air into the pipeline. For these reasons, it is best that a licensed contractor perform this winterization method.
 
This method uses an air compressor with a CFM (cubic foot per minute) rating of around 80-100 for a mainline of 2 inches or less. This type of compressor can be rented at a local rental yard. The compressor itself is attached to the mainline. Please note that compressed air should never be blown through a backflow device.
 
To start the blow out process, shut off the irrigation water supply. Make sure that the compressor valve is in the closed position when you attach the air compressor hose directly to the fitting. Next activate the station on the controller that is the highest in elevation and the furthest spot from the compressor. Next, close the backflow isolation valves. Next, slowly open the valve on the compressor itself. The blow out pressure you use should always remain below the maximum operating pressure and never above 80PSI.
 
Each zone you work on and activate should be followed by working your way from the closest station to the compressor. Activate each until no water can be seen exiting the sprinkler heads. This will take about two minutes per zone. Once that station is dry, do not continue to push compressed air through that head as this can cause friction and could cause damage.
 

Other Things to Consider

Once you have removed all of the water from the irrigation system, make sure that you disconnect the compressor and release any air pressure that is left off. If your backflow device has a ball valve, make sure you open and close the isolation valves many times to make sure that any trapped water has been removed. Leave the valves at a 45 degree angle and open the test cocks entirely.
 

Preparing The System for Blowout

1. Always shut off the water supply to the signal control tube and drain all of the field tubing.
2. Leave the power on and the switch on the off position on any outdoor controllers.
3. For indoor controllers, leave the power on with the dial on off.
4. If you have rain sensors on your sprinkler system, maybe place a plastic bag over the sensors to keep water from freezing in the bowl or cup that catches the water.

What NOT To Do During Winterization

• Never stand over parts while the system is pressurized.
• Do not leave the compressor itself unattended.
• Don’t allow air pressure to go over 80 PSI for PVC piping systems and 50 PSI for polyethylene piping.
• Never blow out the system through the pump or a back flow. Always first blow out the entire system then drain the backflow or pump.
• Do not leave any manual drain valves open after the blow out process.