What is the minimum operating pressure for sprinklers?

• A. At least 5 psi
• B. At least 8 psi
• C. At least 7 psi
• D. At least 10 psi

Answer: (C)

The main idea here is the minimum pressure needed at the sprinkler head for residential, low-rise systems to ensure reliable operation. In NFPA 13R, the design assumes the hydraulically most remote sprinkler head must have at least 7 psi at the head during activation. This 7 psi threshold accounts for the friction losses in piping and connections so that the sprinkler will actually release water properly and achieve a usable discharge pattern.

Why 7 psi works: it’s low enough to suit typical small-diameter residential piping and modest water supplies, yet high enough to guarantee the sprinkler head can open and deliver water. If the head sees less than this pressure, some heads might not activate correctly or deliver insufficient flow for effective fire control.

Why the other numbers aren’t the best choice for the minimum: 5 psi is below what NFPA 13R considers reliably sufficient for activation, so it wouldn’t meet the standard’s requirement. 8 psi and 10 psi are not incorrect values in practice, but they represent higher-than-minimum pressures; the question is asking for the minimum required pressure, which is 7 psi.