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If freezing temperatures are in the forecast, it???~s time to winterize irrigation systems. For much of the country, this means a November or December deadline for getting the job done. By removing water from the pipes, valves and sprinkler heads, contractors can protect systems from potentially serious damage.
Without winteriztion possible problems could include cracked valves, mains freezing and bursting and backflows that cause damage. Anything that is pressurized can cause damage if winterization is not performed.
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 instead of unplugging it for the winter. If left 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.
The compressed air blowout method uses compressed air to clear water from the mainline pipe, sprinkler control valves, lateral pipes and sprinkler heads. Contractors should be advised to use extreme care when using this method to winterize the irrigation system. Excessive pressure (above 50 lbs. per square inch) can damage valves or sprinkler pipes or can generate flying debris, causing physical injury to the operator. Contractors should never stand over irrigation pipes, sprinklers or valves during this process.
To obtain proper air volume, contractors should 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 as some small shop compressors of two hp may not be adequate. However, air pressure must not exceed 50 psi during the blowout procedure. Using a pressure-regulating valve to avoid over-pressurization, contractors should keep air volume high and air pressure low to minimize the potential for damage.
Contractors should not try to use an air compressor with high pressure (120 psi) and low volume to evacuate water from the system. 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. 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 the sprinkler control valve is opened.
To hook up the air hose, 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 the 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 the system has a timer, follow those guidelines described first.
To winterize the irrigation system using the controller, close the mainline sprinkler shut-off valve (A). Relieve the water pressure on the mainline by activating a circuit or zone from the 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). Set the pressure-regulating valve on the compressor to 50 psi and 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 but contractors should 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 and turn off the controller.
To use the manual drain valve method, the irrigation system must first be properly designed. In a properly designed system, the manual drain valve is installed at the lowest point on the system???~s mainline. Additional manual drain valves should be installed if the 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 overflowing the system.
To manually drain the valve, first turn off the sprinkler system mainline shut-off valve (A) as shown in the accompanying diagram. 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). Repeat this procedure for all manual drain valves on the sprinkler system mainline.
Contractors should note that draining valves using gravity or activating the valves manually does not remove water captured inside the valves. Valves must be disassembled to remove standing water (unless they are winterized using blown compressed air). Manual valves should be left in the open position throughout the winter to prevent repressurization.
Some sprinkler heads have both side and bottom pipe inlets. If the side inlets are used, install a drain valve on the bottom inlet to prevent the case from freezing. Sprinkler heads with built-in check valves to prevent low head drainage must be disassembled or blown out with air.
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. These drain valves simply screw on using 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 the system is shut off, 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).
Contractors should not try to use an air compressor with high pressure (120 psi) and low volume to evacuate water from the system. 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. 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 the sprinkler control valve is opened. This dangerous practice places severe stresses on all components of the system. Never run the compressor without at least one sprinkler control valve open.
To hook up the air hose, 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 (point ???C???? in the previous diagram). This connection should be located as close to the water source as possible. Check with the air compressor manufacturer for the correct procedure and equipment hookup.
Rod Waller is a Contractor Account Manager for Rain Bird Corporation in Florida.
80: PSI, the maximum recommended pressure for air compressors when blowing out an irrigation system. Anything over 80 PSI can damage the components of the irrigation system.
30 to 45: Minutes, the expected amount of time it would take to winterize a residential irrigation system, using the ???blow out???? method.
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
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