Which statement about elevation loss estimation is correct when considering PRVs on a standpipe riser?

Which statement about elevation loss estimation is correct when considering PRVs on a standpipe riser?

• A. Not PRV: The roof; PRV: The highest floor
• B. Not PRV: The highest floor; PRV: The roof
• C. Not PRV: Ground level; PRV: The top floor
• D. Not PRV: The highest floor; PRV: Ground level

Answer: (B)

When a pressure-reducing valve (PRV) is on a standpipe riser, elevation head is treated in two parts: the portion of the riser below the PRV where the water column climbs without regulation, and the portion above the PRV where the valve sets the downstream pressure. The part below the valve is what you would normally estimate for elevation losses up to the highest occupied floor. Above the valve, the PRV limits pressure, so further vertical rise to the roof does not add the same elevation head to the discharge calculation; you account for that section in terms of the valve’s pressure setting rather than additional elevation gain. Therefore, the part of the riser without a PRV extends up to the highest floor, and the portion that contains the PRV extends to the roof. This matches the idea that the non-PRV segment ends at the highest floor, with the PRV located at the roof.

When a pressure-reducing valve (PRV) is on a standpipe riser, elevation head is treated in two parts: the portion of the riser below the PRV where the water column climbs without regulation, and the portion above the PRV where the valve sets the downstream pressure. The part below the valve is what you would normally estimate for elevation losses up to the highest occupied floor. Above the valve, the PRV limits pressure, so further vertical rise to the roof does not add the same elevation head to the discharge calculation; you account for that section in terms of the valve’s pressure setting rather than additional elevation gain.

Therefore, the part of the riser without a PRV extends up to the highest floor, and the portion that contains the PRV extends to the roof. This matches the idea that the non-PRV segment ends at the highest floor, with the PRV located at the roof.