Watch Out for Winter

If freezing temperatures are in the forecast, it's time to winterize your irrigation system. By removing water from the pipes, valves and sprinkler heads, contractors can protect systems from potentially serious damage in cold climates. If this isn't done, possible problems could include cracked valves, mains freezing and bursting, and back flows that cause damage. Anything that is pressurized can cause damage to the system if you don't winterize it.

There are three common winterization techniques: manual drain valve, automatic drain valve and a compressed air blowout. It is important to remember that no matter which method you choose to remove water from the irrigation system, controller protection is also critical to the winterization process. It's better to keep the controller plugged in and switched to the off position than unplugging it for the winter. If unplugged over the winter, some controllers might automatically engage once power is re-connected, which could cause problems if the system is not ready for operation.


To use this method, the irrigation system must be properly designed. Make sure the manual drain valve is installed at the lowest point on your system's mainline. You should install additional manual drain valves if your mainline has multiple low points where water may collect. A ball valve, gate valve, “stop and waste” valve or simple threaded pipe with a cap can provide drainage. It's important to make sure piping is properly sloped to drain. If the valve is outdoors, it should be installed over a “dry well” (underground pit filled with gravel) to drain water away from the piping. If the valve is installed indoors, make sure you can drain a volume of water without flooding or overflow.

To manually drain the valve, first turn off the sprinkler system mainline shut-off valve (A) (see Figure 1 on page C14). Then open one of the sprinkler system control valves, either manually or electronically from the controller, to relieve pressure on the sprinkler system mainline. Slowly open the manual drain valve (B) (see Figure 1 on page C14). Repeat this procedure for all manual drain valves on the sprinkler system mainline.


The automatic drain valve is a spring-loaded device installed on sprinkler heads or lateral pipes. The drain valve opens every time the system is shut off and drains all water from the pipe. When the system is pressurized, water presses against the sealing mechanism, shutting the valve and allowing water to flow through the pipe and to the sprinklers.

Automatic drains should be installed after or downstream of the sprinkler control valves at the low points in the sprinkler lines. Usually one or two drains per line are adequate. The drain valves simply screw on using ½- or ¾-inch male pipe threads. Teflon tape wrapped two or three times around the connection ensures a proper seal. A small dry well directly beneath the drain assists with drainage for poorly draining soil.

Because automatic drain valves remove water every time you shut off the system, no manual intervention is required for this stage of winterizing. Simply check for excessive puddling on the soil surface, which may indicate that one of the drains has become stuck open during sprinkler operation. As with the manual method, draining or activating remote control valves from the controller does not remove water captured inside the valves. Valves must be disassembled to remove standing water (unless you winterize using blown compressed air).


Use extreme care when blowing out the system. Excessive pressure (above 50 psi) can damage valves or sprinkler pipes or can generate flying debris, causing physical injury to the operator. Never stand over irrigation pipes, sprinklers or valves during this process.

This method uses compressed air to clear water from the mainline pipe, sprinkler control valves, lateral pipes and sprinkler heads.

To obtain proper air volume, use a compressor capable of providing 10 to 25 cubic feet per minute (CFM) of air volume. It is important to rent or buy the right air compressor for the job. Some small shop compressors (2 hp) may not be adequate; however, air pressure must not exceed 50 pounds per square inch (psi) during the blowout procedure. Use a pressure-regulating valve to avoid over-pressurization. Air volume should be high and air pressure should be low to minimize the potential for damage.

Do not try to use an air compressor with high pressure (120 psi) and low volume to evacuate water from the system. Also, don't compensate for a small compressor by filling the compressor's holding tank while the mainline is closed to create a surge of pressure to blow the line clean when you open the sprinkler control valve. This dangerous practice places severe stresses on all components of the system. Never run the compressor without at least one sprinkler control valve open.

(Note: Even if the system can withstand 120 psi of water pressure, similar air pressure will damage the system. The viscosity of air is much lower than water, generating much higher stresses.)

The sprinkler system mainline should offer a separate quick-connect fitting, manual gate valve, plugged “tee” or capped pipe in the line specifically for the air hose. This connection should be located as close to the water source as possible. Check with your air compressor manufacturer for the correct procedure and equipment hookup.

Blowing out a system using a timer is safer than activating the valves manually. If your system has a timer, follow the guidelines described first.


Close the mainline sprinkler shut-off valve (A) (see Figure 1 on page C14). Relieve the water pressure on the mainline by activating a circuit or zone from your controller. Activate the circuit that is farthest from the air connection before letting air into the piping. Always keep a sprinkler zone control valve open, from start-up to compressor shutdown. Attach the compressor hose to the blow-out adapter (C) (see Figure 1 above). Set the pressure-regulating valve on the compressor to 50 pounds per square inch (psi). Never exceed 50 psi. Turn on the compressor. Gradually increase the flow of air until all the sprinkler heads pop up. The amount of flow or volume required will depend on the length of pipe and number of heads. Do not blow any circuit more than two minutes at a time. Sustained heat from the compressed air may damage pipe and sprinkler drive mechanisms that use water for lubrication and cooling. Switch to another station or zone by advancing the controller to the next circuit. Do not turn the controller off at any time during this operation unless the compressor is first shut off.

To ensure that lines adequately drain, repeat the cycle two or more times, activating each zone from the controller until nothing more than a fine mist appears from the heads. After blowing out all the zones, leave one zone on while shutting down the compressor. You may then unhook the compressor from the mainline. Turn the controller to “OFF.”


(Note: Use this option only if your system does NOT have electric remote control valves.)

If your system does have electric remote control valves, activate the valves from the controller. Using remote controls is safer because you are not close to irrigation components, which can discharge debris during blowout. Always wear eye protection and never stand over irrigation pipes, sprinklers or valves during this process. To activate valves manually for the blowout, close main sprinkler shutoff valve (A) (see Figure 1 on page C14).

Relieve the water pressure on the mainline by slowly opening the manual shut-off handle on one of your irrigation zone control valves. Attach the compressor hose to the blow-out adapter (C) (see Figure 1 on page C14). Set the pressure-regulating valve on the compressor to 50 psi. Never exceed this setting. Manually open the irrigation station you want to blow out before turning on the compressor. Gradually increase the flow of air from the compressor flow valve — not from the sprinkler control valve — until sprinkler heads pop up. The flow or volume required will depend on the length of the pipe and the number of heads. Do not blow any circuit more than two minutes at a time. Sustained heat from the compressed air may damage pipe and other components. After two minutes, turn the compressor off and allow the air to completely purge from the compressor tank and sprinkler system.


Turn on the next irrigation control valve you wish to winterize before turning off the irrigation control valve you have just blown out. Repeat steps until you have blown out each zone at least twice and only a fine mist is blowing from each station. After turning the compressor off, allow any air in the storage tank or irrigation components to disperse before approaching the air hose or valves. Unhook the compressor from the adapter to the sprinkler mainline.

Taking the time to winterize all parts of a sprinkler system will not only protect it this winter, but will also extend the life of the irrigation components so they can serve for years to come.

Rod Waller is a contractor account manger for Rain Bird Corporation in Florida.

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