Pull (4) dry pendants dated 2008. Due to these being in service for more than 10 years, samples will need to be sent to UL for testing. New heads will be installed in place of the ones pulled. NFPA 25 (126.96.36.199.6) Dry sprinklers that have been in service for 10 years shall be replaced or representative samples shall be tested and then retested at 10-year internals. Assess the issue with the backflow. Per Mike Trevoort, the compressor was running every 20 minutes a while back and is not running every 4 minutes.