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There are two ways to winterize a sprinkler system - manually drain the
system or blow it out using an air compressor.
In warm climates it is usually sufficient to just shut off the water supply and drain the water from the pipes. However, manually draining the system often leaves water that collects in the low spots and if it freezes it will expand, bursting the pipes. So, in cold climates it is important to remove as much water as you can. This is best accomplished by blowing out the system with compressed air.
Winterizing sprinkler systems using the blow out method is a
job most handy DIYers can handle. However, forcing pressurized air
through a sprinkler system can cause damage to components and is
hazardous if not done properly. if you are unsure about any of the
steps I highly recommend hiring a professional irrigation contractor to
do the job for you.
Step 1 Turn off the water supply by closing the main valve. The main valve is usually located near the water meter. In mild climates it will often be found in a valve box that sits inside the property line. In cold climates it will be located in the basement - look for a tee off of the house water supply line.
Step 2 Open the drain valves and let the water in the system drain. Close the drains before pressurizing the system with air.
Step 3 Hook up the air compressor. Tie into the mainline via a quick coupler, hose bib or other type connection, that is located beyond the backflow preventer. Do not hook the air compressor up to the backflow preventer. Blowing air backflow preventer tends to wear out the rubber gaskets.
Slowly bleed air into the mainline, taking care not to blow any sprinkler heads or valves out of the ground :)
Step 4 At the control box, set all of the zones to run for two minutes. Run one zone at a time allowing the compressed air to blow water out of the system. When the zone is down to 2 or 3 heads blowing mist move on to the next zone.
Cycle through all zones at
least twice to make sure most of the water is out of the pipes. Shut
off a zone once it is dry - the friction from blowing air through a dry
zone will damage parts.
Step 5 Turn the control box to the "Off" position or
unplug it. This will prevent the controller from accidentally opening
the valves over the winter and damaging the solenoids by running them
Step 6 After blowing out the system, check the backflow
preventer to make sure the water has drained. Opening and closing the
valves a couple of times will help it drain. Leave the valves on the
backflow prevention device half open over the winter.