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Winterizing an Irrigation System

Avoid a big mess this spring. Follow these steps to prepare your irrigation system for cold weather.

March 6, 2018

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Each year when the leaves start to fall and temperatures drop we know it's time to shut down irrigation systems. In the colder climates irrigation systems must be winterized to avoid damage caused by freezing temperatures. By taking the necessary steps to protect irrigation systems now you can avoid costly repairs in the spring.

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 or water can be trapped in low spots. For the added safety and fairly low cost of winterizing with an air compressor it's not worth the gamble. Blowing out an irrigation system with an air compressor has been proven to be the best method in use today.

The following is the procedure for winterizing a typical irrigation system. Throughout the country the products and scenarios may differ but generally the sequence of procedures remains the same.

First and foremost turn off the water! There will always be a master shut off valve somewhere. The basement crawl space or utility room would be the first place to 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 possible). This will alleviate the pressure in the system and give you a head start on the winterizing process. Usually opening a hose bib or drain on the backflow preventer will do nicely. Sometimes there is a drain inside the house. Don't forget 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 it's time to hook up the compressor.

The compressor size being used should depend on the system size. Usually bigger is better (and faster). A smaller compressor can work but it might take a while. Recommended compressors should deliver a minimum of 60 psi at 15 cubic feet per minute (CFM). 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 might lack.

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 the compressor hose can be attached. It will probably be the same drain used in the previous step. Make sure all the other drains are closed (if you opened them in the previous step) except for the drain where the hose will be attached. Sometimes you have to use a little ingenuity to make up a fitting to attach the air hose to the drain. It's not usually a standard fitting (unless you're 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 you do not need that much pressure to blow out a system. Actually never blow out an irrigation system with more than 80 psi. Be warned anything over 80 psi can damage the components of the irrigation system. A good rule of thumb is to use the same amount of pressure used for the house water pressure often around 60 psi. This will avoid any risks of using too much pressure.
Now hook up the compressor and start winterizing. It's best to start with the zone furthest away and work your way back to the nearest zone. Or start on the zone at the highest elevation point usually on top of a berm or hill. For this example let's assume that zone number 10 is the furthest away. 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 you usually do not have to get every single drop of water out of the system. If you continue to blow out the system (even though all the water is out) heat from the air could damage the components of the irrigation system. It's better to get the majority of water out but not continuously run the compressor striving to get every drop of water out. A little residual water left in the zone will not hurt.
It is recommended that you blow out each zone twice with two short cycles as opposed to blowing out each zone once with a long cycle. This reduces your margin of error because there is less of a chance that the compressor was left on too long or a zone was missed.
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. You most likely we blew air through it in the previous steps. Open all the drains and leave them open. Over the winter it's best to leave the ball valves or drains (on the backflow preventer) at a 45-degree angle. Sometimes condensation can build up inside the ball valve 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 to winterize. But this could fluctuate depending on the size of the compressor being used and the size of the irrigation system. Obviously there are many more scenarios that can add to the winterization process. Pumps fertilizer injectors etc. could all add to the winterization process.
Remember "An ounce of prevention is worth a pound of cure." This definitely applies to winterizing an irrigation system. Knowing that your customer's irrigation systems will start and operate without any headaches in the spring is definitely worth a pound of cure.