Coffee Break Training: Automatic Sprinklers: Aboveground Sprinkler Pipe Pneumatic Testing [open pdf - 488KB]
"The importance of hydrostatic testing newly installed or renovated sprinkler systems was discussed in Coffee Break Training 2009-15. These tests are conducted to assure the sprinkler fitters' work will not result in any leaks, or if leaks are detected, they are repaired promptly. Normally, wet pipe sprinkler systems are installed in environments where the ambient temperature will not dip below 40 F (4.4 C). This threshold is intended to protect the wet pipe sprinkler system from low temperatures that will result in freezing. As water freezes, it expands inside the sprinkler pipe and may result in small leaks or even catastrophic failure. In those areas where lower temperatures can be expected, dry pipe and preaction systems may be employed. Rather than water-filled overhead pipes, these have pressured air or nitrogen inside the pipe to hold back water pressure or monitor the conditions within the system."
Coffee Break Training - Fire Protection Series No. FP-2013-16
United States Fire Administration: http://www.usfa.fema.gov/