These are common problems that can easily be corrected.
A nozzle dripping or not spraying can be caused by improper pressure setting. If there is no pressure, that could be a clogged filter or bad check valves.
First make sure that the aluminum filter attached to the end of the large pick-up valve is clean and free of all debris and the disc in the end of the large valve is not stuck closed. You can check this by pushing it with a pen while you have the filter off.
Since 1979, professional horsemen have trusted Shoo-fly insecticides and automatic insect control systems to keep their barns and stables clean and pest-free. Many of our systems have been in continuous operation for decades and are still going strong.