As the fall season begins to approach winter, it is time to get serious about the winterizing of your irrigation system. The winterizing concept seems simple enough to perform. However, it may not be as simple as it may first appear. This must be done correctly to assure there are no costly repairs and replacements to make in the spring at system start-up.

Winterization primarily consists of expelling all the water from the irrigation system and equipment. This is necessary because water freezing during cold weather will break pipes, fittings, valves, sprinklers, pumps, etc.

Most substances contract as they get cold; however, when water cools, it contracts only until it reaches a temperature of 39 degrees Fahrenheit. Upon further cooling to 32 degrees Fahrenheit, water expands as it turns to ice. Water expands and increases in volume by one-eleventh, so 11 cubic feet of water will form approximately 12 cubic feet of ice. This expansion force is sufficient to cause pipes and fittings to burst, valves to crack, and sprinkler and pump cases to split open.

Draining the system may be accomplished by the use of either manual or automatic drain valves which rely on gravity to drain the water from the system. Of course this relies on a properly installed system laid to grade with no humps in the pipe to trap water in low areas. Also, if you have electric valves in the system, there is no way to drain the water off the top of the diaphragm of the valve. As this manual gravity draining happens underground, there is no way to be sure that enough has been drained to prevent freeze damage. The only positive way to be sure enough water has been expelled from the system is by using compressed air to "blow" the water out.

The most important thing to remember when "blowing out" your system for winterization is that air VOLUME and not air PRESSURE is the most critical element. If an insufficient volume of air is used, after having forced some water out, the air will ride over the top of the water. This will result in the remaining water draining into low spots and subjecting your system to freeze damage. Ideal pressures are in the range of 40 psi to 80 psi for the air compressor with 80 psi being the maximum.

Rule of Thumb: If the sprinkler heads stay up after the water is blown out, you are using the right size compressor.

The idea is to "blow" your system out using only the volume of air equivalent to the maximum gallons per minute (G.P.M.) for which your system is rated. In other words if you normally run one zone at a time when irrigating, you should blow out in the same way. If you try to do more, the excess velocity of flow and added friction will heat up the pipe and fittings to a point where they possibly could melt. If the pipe and fittings do not burst during this operation, they will be damaged and their life greatly reduced. As a result, failure will occur sometime in the future.

Start with the pump (or backflow preventer if you have a domestic water system). Drain your pump, remove it from the system and store inside. If this is not possible, the next best thing is to drain the pump and wrap it to insulate from the weather. Your backflow preventer can be handled in the same way, except you will need to turn off the water to your system. Usually a stop and waste valve is used for this. This stop and waste valve is designed to drain the water from underneath the inlet of your backflow preventer. If possible, it is best not to blow out the system through the backflow preventer. The rubber seals inside can easily melt from the heat of the air.

• The system should be blown out twice to make sure all the water is purged.
• Don't use too small an inlet for your air line. The smaller the hole the faster the air has to travel through it and the more heat produced; for instance the test cocks on your backflow preventer are 1 1/8 or 1 1/4 inch. In a normal residential system, this would be the minimum size inlet you would use. A larger inlet would be needed for larger systems.
• After purging the system, leave all the valves on your backflow preventer half open. This will help keep the backflow preventer from freezing and splitting during the winter.
• If possible, tie into a metal fitting to help dissipate some of the heat from blow out.
• If you have an automatic system, your controller should remain powered during the winter. Heat from the transformer can help keep moisture down and protect components in the controller from corrosion. The controller should be programmed to run through a minimum cycle once a week to help keep solenoid plungers from sticking.

It is important to remember it is much less costly and much less labor intensive to properly and efficiently winterize the system in the fall than to repair damaged fittings, piping, valves, sprinklers and other components in the spring.