We have an underground sprinkler system but have never used it (don't like the layout due to re-landscape by previous owner) until this summer. We turned on the water supply but found the backflow preventer had broken. I did not turn on the valves. I can only see few heads have water out very short. We decided not to use it. Now we want to make sure we can winterize it. I have Craftsman 6 Gallon air compressor 150 psig (SCFM 3.7@40 psig, 2.6@90 psig). But when I turned on and tried, nothing come out from the sprinkler heads. I am not sure if did anything wrong or the compressor is too small.