A garden sprinkler system makes maintaining a yard much easier, but you do have to take care to drain them of any remaining water come late fall if you live in an area with cold winters.
If too much water remains in your sprinkler lines, then that water will freeze, and the resulting expansion can break the plastic lines laid below the ground. You can avoid having to do expensive repairs on your sprinkler system by winterizing it before the cold weather sets in, and one of the best ways to do just that is by using an air compressor to blow out sprinklers.
You can always hire a service company to do it for you, of course – but if you have your own air compressor for your workshop or garage, you can potentially save hundreds of bucks every season by learning how to do it yourself.
Learning how to properly using an air compressor to blow out sprinklers means understanding how to put out just the right amount of pressure into your sprinkler lines one zone at a time.
Too much air pressure or volume and you run the risk of blowing out your pipes and connections. The more common case is when homeowners try to blow out a number of sprinkler heads that’s more than what their air compressor can handle.
With enough experience, you will soon understand how to spread out the load needed to blow out just the right size of your sprinkler system using the air compressor that you have on hand.
1. Choose the Right Size Air Compressor for Your Sprinkler System
If you are still at the stage where you’re just shopping around for the air compressor to winterize your sprinkler system with, then you have the chance to get one that has enough volume to get the job done.
To properly blow out your sprinkler system, you may need to have an air compressor that can sustain enough volume to blow air into a section two minutes at a time, or even longer.
For that kind of task, you will need an air compressor that can put out a decent volume of air for extended periods of time – ideally, your air compressor should be capable of providing at least 5 CFM, or cubic feet per minute.
Some sprinkler systems will use pipes that are 3/4 inches in diameter or even up to an inch in diameter in some cases – these systems will need an air compressor with a larger CFM rating compared to sprinkler systems that use 1/2 inch lines.
For extensive systems with large pipes, many yard professionals prefer winterizing them using an air compressor that is capable of sustaining at least 10 cubic feet per minute.
Aside from the volume, capacity is also important to ensure that your air compressor is capable of sustaining that CFM for minutes at a time. Go for models that have dual tanks, especially if you have larger sprinkler lines.
Air compressors need time to charge its tanks, and you may run out of air before your air compressor can finish blowing out a section of your sprinkler system. Yard care professionals recommend having a tank capacity of at least 10 gallons so that your air compressor motor will have plenty of spare capacity to keep up the air pressure in the tank.
If you have an existing air compressor, it’s a good idea to test it out first to check if it has the tank size needed to winterize your sprinkler system. One good way to find out is to run your air compressor at 5 CFM or more for a full 2 minutes or more – the typical time that it takes to blow out a section of your typical yard sprinkler system.
Check that the pressure remains more or less stable during that time. If the pressure meter drops off in that span of time, you may need to get (or rent) another air compressor that is capable of finishing the job.
Blowing out sprinklers and sprinkler systems is a task that involves a lot of water – things can get really wet while you are in the middle of the task. While you can certainly use an electric air compressor to do the job, there is the potential risk that your extension cord will get wet.
Gas powered air compressors, on the other hand, do not need extension cords to function and therefore will not expose you to the risk of electric shock.
Another plus of gas motors – you can run them just about anywhere on your yard, which makes them even more suitable for winterizing sprinkler systems on larger yards where an electrical outlet may be out of reach.
2. Setup Your Compressor and Hook It Up To Your Sprinkler System
The first step is to turn off the water supply to your irrigation system, by closing off the main water valve leading to the rest of your sprinkler lines.
After doing that, you can confirm that there is no water supply going into the pipes by opening the hose bib at the sprinkler system’s main line. Doing this also relieves any remaining water pressure in the pipes, and will also allow you to drain any excess water.
While your sprinkler system is getting drained of excess water, you can take this time to set up your air compressor. Connect the air compressor to its power source or fill it with fuel and start it up, depending on the type of air compressor that you have.
Follow the user’s manual on how to set your air compressor to the proper air pressure for your sprinkler system. It’s important that you do not introduce more pressure into your underground sprinkler lines than it can handle.
Sprinkler lines made of rigid PVC pipes and connectors will be able to handle a maximum of 80 PSI, or pounds per square inch. If your sprinkler lines are made of flexible black polyethylene pipes, then you should set your compressor to a maximum of 50 PSI.
Then, locate the pressure vacuum backflow device on your irrigation system – it will usually be a large round device at the top of your sprinkler mainline setup. Close off both of the valves leading to the backflow preventer.
You can now remove the plug on the blow-out port, which will expose an air hose adapter. Connect the air hose from your air compressor into a quick connect hose adapter and use that to connect your air compressor to your sprinkler system.
3. Blow Out Your Sprinkler System Zone by Zone
If you have a sprinkler system that is large enough to have several zones, then it’s likely that your air compressor may not have enough power to blow out your entire irrigation setup all at once. Using your sprinkler system, however, it’s possible to send your air compressor output to one zone at a time.
You can have a more accurate idea of how much CFM it would take to blow out a zone if you have a copy of your sprinkler layout showing the gallons per minute output of each sprinkler head. If you divide the total water GPM of a zone by 7.5, then that will give you the CFM required to blow out that zone.
To blow out your irrigation system one zone at a time, first set your system timer to open just the one zone you are aiming for, and close off all the others. If your irrigation system is equipped with manual drain valves, then you will need to open those first.
Connect your air compressor to the blow out line connected to that zone, and charge up your air tank. Once the system timer opens that zone, then you should see the sprinkler heads in that zone pop up and begin spraying out the remaining water inside the system.
Blowing out a zone can take as long as two minutes, but it’s important that you only blow out the zone in the time it takes to run them dry. Sprinkler heads usually have plastic gears and components, and they need water to lubricate and cool them down – running them with dry air for extended amounts of time can cause them to overheat and melt.
It’s also important that you blow out as much water as you can from your sprinkler lines, especially if your system uses pipes with smaller diameters. If you need to, you can move on to the next sprinkler zone to let the first zone cool down first – you can then go back to it later to blow out any remaining water a second time.
4. Disconnect Your Air Compressor
Once you have finished blowing out your irrigation zones, you will need to bleed off any excess air pressure in the lines.
Disconnect the air hose from the blow out port and leave it open for a while to release any remaining air pressure in your sprinkler system lines. Now that the pipes are dry, you can now move on to the next steps you need to complete your yard irrigation winterizing preparations.
