question winterization lawn sprinkler system

hi,
I recently bought a house and am trying to determine if I must do any winterization for the sprinkler system.
I live in northern utah (does get cold in the winter). my sprinker lines are made of poly-pipe (the black pipe).
I surely want to avoid pipes freezing and bursting (if that is indeed possible).
a friend earlier today told me if my sprinker lines are poly-pipe then it is very unlikely they would freeze and burst).
I all the sprinkler line are underground.
can someone tell me if I need to do any winterization or am I OK to do nothing (but shutoff the main water valve)?
all responses are much appreciated.
BA kaysville, UT
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BA said:

You need to blow out all of the lines with compressed air. As it's your first year with the system, it's probably best to hire a sprinkler service company to do it.
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Most new installiations include the service for free the first year, too bad his didnt! But defently get it blown out. Pipe if filled with water WILL burst if frozen.
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