The old requirement/standard for the installation of pressure relief valves was only for gridded systems. Since 2010, NFPA 13, Standard for the Installation of Sprinkler Systems requires relief valves for all wet-pipe systems. The current 2013 version of NFPA 13 Section 7.1.2 now states:
7.1.2 Relief Valves.
18.104.22.168 Unless the requirements of 22.214.171.124 are met, a wet pipe system shall be provided with a listed relief valve not less than 1⁄2 in. (12 mm) in size and set to operate at 175 psi (12.1 bar) or 10 psi (0.7 bar) in excess of the maximum system pressure, whichever is greater.
126.96.36.199 states where auxiliary air reservoirs are installed to absorb pressure increases, a relief valve shall not be required.
The purpose of the relief valve is to prevent excessive pressure build up within the automatic sprinkler system. For example, excess heat can cause the water within the pipe to expand and possibly rupture the pipe, fittings or sprinklers. If most of the air within the piping was relieved, due to the installed relief valve, there would be no air pockets within the piping where the air could expand.
Most sprinkler piping and fittings are rated and listed for 175 psi. Adding the relief valve will prevent failure of the system components.
The relief valve can be located anywhere on the system. It can be open to a drain line and installed within the inspectors test connection.
There are several FM Global approved relief valves listed on the FM Approval Guide.
Risk Logic can conduct a review of your sprinkler system. Please feel free to contact us.