How to Winterize an Irrigation System
By Damian Zawacki

Well, its that time of year again. The leaves are starting to fall and temperatures are starting to drop. This also means its time to shut down our irrigation system. Here in the northeast (the writer of this article is from Michigan) our irrigation systems have to winterized to avoid damage caused by freezing temperatures. By taking the necessary steps for protecting our irrigation system now, will avoid costly repairs in the springtime.

First there are some claims of irrigation systems being self-draining. This might be true, however is it worth the gamble? Drains can get clogged or forgotten to be opened, water can be trapped in low spots; the list goes on and on. For the added safety and fairly low cost of winterizing with an air compressor, it's not worth the gamble. Blowing out our irrigation system with an air compressor has been proven to be the best method being used today.

The following is the procedures for winterizing a typical scenario here in Michigan. Obviously, throughout the country the products and scenarios may be different, but generally the sequence of procedures are usually the same.

First and foremost, turn off the water! There will always be a master shut off valve somewhere. In the basement, crawl space or utility room would be the first place I would check.. Turn it off and tag it for future reference. Placing a tag on the valve indicating it's for the irrigation system will prevent any mishaps that could happen for an unknowing homeowner.

Next manually drain the system (as much as we can). This will alleviate the pressure off the system and give us a head start on the winterizing process. Usually, opening a hose bib or drain on the backflow preventor will do nicely. Sometimes there is a drain inside the house. Obviously, we have to use a bucket to catch any drained water. Warning, you might get wet. Opening a drain under pressure will shoot water out for the first few seconds, until the pressure locked in the system dies down. Once the pressure has been bled from the system and the water has drained down a little, its time to hook up the compressor.

We will have to find an access to the system where we can hook up the air compressor. There has to be a hose bib or a drain somewhere after the main shutoff valve where we can attach the compressor hose. It will probably be the same drain we used in the previous sequence. Make sure all the other drains are closed (if we opened them in the previous step) except for the drain we are attaching our hose to. Sometimes we have to use a little ingenuity to make up a fitting to attach from the air hose to the drain. It's usually never a standard fitting (unless your really lucky).

Prior to hooking up the air hose to the irrigation system, let the Air compressor charge itself. Usually, most compressors can charge up to 120 PSI or more. However, we do not need that much pressure to blow out our system. Actually, never blow out an irrigation system with more than 80 PSI Max. Be warned, anything over 80 PSI can damage the components of the irrigation system. Actually, I prefer to keep my air pressure around 60 PSI. Why? Because my house water pressure is 60 PSI, thus I should use the same amount of air pressure for winterizing. This will avoid any risks of using too much pressure.

Now hook up the compressor and start winterizing. Its best to start with the furthest away zone first and work our way back to the nearest zone. Or start on the zone at the highest elevation point. Usually on top of a berm or hill. Now, lets guess that zone number 10 is the furthest away zone. We turn zone number 10 on at the controller for 2 minutes and let it go. Now, 2 minutes might be too long or not long enough. Watch the water as it comes out of the sprinkler heads. Slowly the water will turn into a mist. Then the mist will turn into air. At this point all the air is out of zone number 10. Turn off zone number 10 and continue on to the next zone.

Please note, usually we do not have to get every single drop of water out of the system. If we continue to blow out the system (even though all the water is out), the heat from the air could damage the components of the irrigation system. Its better to get the majority of water out, but not continuously run the compressor trying to strive to get every drop of water out. A little residual water left in the zone will not hurt.

I recommend blowing out each zone twice with two short cycles as opposed to blowing out each zone once with a long cycle. This leaves less room for margin of error. I rather leave out a chance of having left the compressor on too long, or missing a zone, thus possibly damaging the system.

The compressor size needed depends on the system size. Usually bigger is better (and faster) but a smaller compressor can work, but it might take awhile. I usually recommend a compressor being able to deliver a MINIMUM of 60 PSI at 15 CFM's. CFM's is Cubic Feet per Minute. This is what actually displaces the water. Most compressors will not have a problem delivering the PSI, but it's the CFM's where they will lack.

Next, we have to check the backflow preventer. Most systems have a backflow prevention device installed at the beginning of the system. Make sure it's completely void of water. Which it should be, because most likely we blew air through it to winterize the system. Open all the drains and leave them open. Over the winter, it's best to leave the ball valves or drains (on the backflow preventor) at a 45-degree angle. Sometimes condensation can build up inside the ball valve, thus cracking it when the temperature drops below the freezing point. Leaving the ball valves at a 45-degree angle will help prevent this.

The average residential system should take about 30 to 45 minutes. But again, this all depends on the compressor size and the irrigation system size. Obviously, there are many more scenarios that can add to the winterization process. Pumps, fertilizer injectors, etc. all add to the winterization process. However this article covers the general sequence of the process.

Remember, "An once of prevention is worth a pound of cure". This definitely applies to winterizing an irrigation system. Knowing that in the springtime our system will start and operate without any headaches is definitely worth a pound of cure.