As summer comes to an end and fall approaches, it is time to start thinking about preparing your irrigation systems for winter. Water expands when it freezes. Since automatic irrigation systems are usually buried only about twelve inches below the surface of the soil, water left in an irrigation system in freezing climates over the winter, even a mild winter, will certainly freeze — causing damage to pipes, fittings, valves, and sprinklers. Damage caused by a frozen irrigation system can be expensive and time consuming to repair next spring. Preventing winter damage by properly winterizing the irrigation system is important.

Using compressed air to force water out of the irrigation system is the most common method of winterization. However, irrigation systems equipped with automatic or manual drain valves do not require compressed air to winterize. Only the installing contractor will know if an irrigation system is equipped with automatic or manual drain valves. If you are not sure what type of irrigation system you are winterizing, then use compressed air. Using compressed air on an irrigation system equipped with automatic or manual drain valves will not harm the components of the irrigation system, and will ensure the irrigation system is properly winterized.

Selecting an Air Compressor

Sulliar 185 Portable Air Compressor

A properly sized air compressor is critical in effectively and efficiently blowing air into the irrigation system, forcing any water out. Air compressors are available in various sizes. The most common portable air compressor, which represents roughly 80% of the portable air compressors going into rental fleets today, is the 185 portable air compressor. This machine is rated at 185 cfm at 100 psi at full load. You can find one through a contractors’ equipment rental shop that is more than adequate to get the job done for most residential and commercial irrigation systems. Smaller 5 h.p. electric air compressors, although capable of delivering 100 psi, are not capable of delivering enough volume of air to adequately winterize an irrigation system.

Compressed Air Winterization

The first step in winterizing an irrigation system is to shut off the water to the irrigation system at the point of connection. The system shut-off valve may be a ball valve or gate valve located in the basement or directly after the water meter. Then open a zone valve to relieve the system pressure. Attach the air hose from the air compressor to the blow-out point. The blow-out point is usually located directly after the backflow device. The blow-out point may be a quick coupling valve, a hose bib, or a boiler drain. In this technical drawing the blow-out connection is the quick-coupling valve located in the valve box.

A note of caution: The expanding air coming from the air compressor into the irrigation system will get hot and may melt the plastic pipe. Carefully check the temper- ature of the air-hose connection at the blow-out point. Slow down or stop momentarily if it feels too hot! Cycling through each zone two or three times for short intervals will prevent too much heat buildup.

Air Compressor Settings

Set the pressure regulator on the air compressor at 50 to 80 psi. On smaller residential systems, where the zones are typically about 10 gpm or less, open one electric remote control valve manually and cycle through all the other zones two to three minutes by manually opening each valve or by electrically operating each valve at the con- troller. Opening one valve manually will help to keep the air com- pressor from building up too much pressure while assuring an ade- quate volume of air to thoroughly blow out all the water in the sys- tem. On larger systems it may not be necessary to open one valve manually. Allow the air to flow through each zone until water and water vapor no longer appears from any sprinklers in the zone. Start with the zone with the highest elevation in the system or farthest from the point of connection, blowing out each zone successively toward the point of connection. It is a good idea to cycle through each zone two times to ensure there is no water remaining that might settle into a low point in the lateral pipe.

Automatic Drain System Winterization

Although using compressed air is the most common method for winterizing an automatic irrigation system, there are two other types of automatic irrigation systems. The first type is a system equipped with automatic drains. The automatic drains open when the system pressure falls below 10 psi. For these systems it is usually only necessary to turn off the water. Open a drain valve after the point of connection. Prepare the backflow device and controller for winter as noted below. Some irrigation systems incorporate automatic drain valves on the laterals and manual drain valves on the main line. The manual drain valves will be located in small valve boxes at the end and at low points on the main line. Open the drain valves, and allow the water to drain out completely. Then close the drain valve.

Manual Drain System Winterization

An irrigation system equipped with manual drain valves requires you to locate the drain valve for each zone and the main line. The manual drain is usually located in a small valve box at the end of the zone and at every low point. Also, the main line will have a manual drain at the end of the line and at every low point. Open each drain valve, allowing all the water to drain out, and then close the manual drains. Winterize the back- flow device and irrigation controller as noted below.

Backflow Winterization

Watts Frost Proof Pressure Vacuum Breaker

There are two backflow devices utilized in landscape irrigation systems. The most common is a pressure vacuum breaker. Open the top of the pressure vacuum breaker and remove the internal discs and springs. Storing these components near the irri- gation controller makes them easier to find next spring. Turn the handles on the two ball valves and all test ports to a partially open 45 degree position. Ball valves, when fully closed or fully open, will trap water in between the ball and the valve housing. The valve housing will crack during a freeze if not left partially open.

Some newer pressure vacuum breakers are freeze resistant, with a built-in relief valve to protect the internal components and the body from freezing. It is not necessary to remove the internal components in these devices.

The other type of backflow device used in irrigation system is a reduced pressure principle backflow device, or RPZ. It is usually best to remove this device completely during the winter and store indoors. Then cap the pipes to the irrigation system. If removal of the RPZ back- flow device is not possible, carefully follow the manufacturer’s instructions for winterization. Each manufacturer has specific instructions for winterizing their reduced pressure principle backflow device.

Irrigation Controller and Rain Sensor Winterization

To prepare the irrigation controller for winter, simply turn the contoller to the off or rain shutdown position. You can also disconnect the power and remove the battery but this is not necessary. It is important not to allow the controller to cycle through an irrigation schedule without water in the system because the remote-control valves require water to move through the solenoid assembly to cool the assembly.

If your irrigation system is equipped with a rain sensor or a soil moisture sensor, it is not usually necessary to cover or remove the sensor for the winter. Check with the manufacturer to make sure the sensor does not require any special instructions for win- terization.

Pump Winterization

Submersible pumps, located in a lake or stream, have a check valve at the pump which needs to be removed to make certain the discharge hose does not freeze. It is adviseable to simply remove the pump and discharge hose from water each winter, reinstalling it in the spring.

Centrifigal pumps have a drain valve located at the base of the pump housing that needs to be removed and stored for the winter. The power supply for the pump should also be disconnect- ed to prevent the pump from being accidentally turned on with- out any water. A pump running without water will quickly burn up. Additionally, if the pump is drawing water from a lake or stream, the intake hose has a foot valve located at the base of the suction line. So it is necessary to remove the intake or suction line completely from the water and store it for the winter. Sometimes a check valve is also located on the discharge side of the pump. This check valve needs to be removed and stored for the winter.

Preparing an irrigation system for winter can be a complicated process. A knowledgeable professional is essential to minimize freezing water damage. An improperly winterized irrigation system can be an expensive proposition next spring.