You cannot directly compare a pressure at one flow to a demand at a different flow. Water supply is a curve, not a single point. The residual pressure of 58 psi is measured at 600 GPM. To know the available pressure at the system’s demand of 520 GPM, you must either use the water supply curve (from a flow test with at least two points) or interpolate. Assuming adequacy without this analysis is a common and serious error. The pressure at 520 GPM will be higher than 58 psi, but the exact value must be determined.

On a wet pipe system, the air pressure should only be a small, maintained cushion (typically 5-15 psi) above the water pressure to prevent water column oscillation. An air pressure of 40 psi with a water pressure of 55 psi is only a 15 psi differential, which might be acceptable if intentional. However, the key clue is the compressor short-cycling (‘runs more frequently’). This indicates the air pressure is dropping faster than normal, pointing to an air leak. Since it’s a wet system, a water leak would cause a drop in *water* pressure, not trigger the air compressor. The issue is on the air maintenance side.

While a main drain test does flush some water (option B is a secondary benefit), its primary objective per NFPA 25 is to detect changes in the water supply. By comparing the static and residual pressures from year to year, you can identify if there has been a deterioration in the water supply, such as a partially closed valve, pipe obstruction, or city supply change. It is a key comparative test for water supply reliability.

ESFR sprinklers are defined by their large orifice size and high K-factor (typically K-14, K-16, K-25, etc.) to deliver high volume, high momentum droplets for suppression. A standard 1/2-inch orifice sprinkler has a K-factor of approximately K-5.6. Using a standard sprinkler in an application requiring ESFR performance would be a catastrophic design flaw, as it would not deliver the necessary suppression capability. This is a fundamental specification error.

The scenario describes classic symptoms of frozen piping in a dry system. The valve trips (clapper opens), allowing water into the system. Water flows from the alarm port (on the water supply side of the clapper) because that path is clear. However, water cannot reach the main drain (which is on the system side of the valve) because the intervening piping in the cold attic is frozen solid, creating a blockage. This is a critical and dangerous impairment.

NFPA 24, “Installation of Private Fire Service Mains and Their Appurtenances,” provides specific quantitative leakage allowances. For metallic piping (like ductile iron), the standard allows a leakage rate of 2 quarts per hour per 100 joints and per 100 feet of pipe when tested hydrostatically. This accounts for minor seepage at joints. ‘No leakage’ (0) is impractical, and 1 gallon per hour is the allowance for *nonmetallic* pipe.

NFPA 13 requires a means to drain the system between the controlling valve (like an OS&Y) and any backflow preventer. This is typically the main drain. This arrangement allows the system and the preventer to be drained for maintenance or winterization without having to drain the entire public supply side upstream of the control valve. Installing the backflow preventer directly downstream of the control valve eliminates the location for this required drain connection.

A preaction system is a two-step interlocked system. It requires two independent events to allow water in: first, the detection system (like heat or smoke detectors) must activate, which opens the preaction valve. This fills the piping with air or nitrogen but does not yet release water. Second, for water to actually discharge, a sprinkler must fuse from the heat of the fire. This dual requirement provides an extra layer of protection against accidental water discharge in sensitive areas like data centers or museums.

The fundamental job of the fire pump is to take the available suction supply and boost it to meet the system’s demand. Therefore, the pump must be selected so that its performance curve, when starting from the actual available suction pressure (35 psi residual at the demand flow), produces at least the required 950 GPM at 105 psi at its discharge. This requires analyzing the pump curve with the net suction pressure, not just looking at the discharge requirements in isolation. The other options are administrative or secondary concerns compared to this core hydraulic requirement.

You cannot directly compare a pressure at one flow to a demand at a different flow. Water supply is a curve, not a single point. The residual pressure of 58 psi is measured at 600 GPM. To know the available pressure at the system’s demand of 520 GPM, you must either use the water supply curve (from a flow test with at least two points) or interpolate. Assuming adequacy without this analysis is a common and serious error. The pressure at 520 GPM will be higher than 58 psi, but the exact value must be determined.0