A tall building is zoned so that static pressure at the lowest fixture in each zone stays within the 80 pound per square inch ceiling the code places on the water distribution system. The pressure-reducing valve at the top of a zone is set to deliver 62 pounds per square inch. Using 0.433 pound per square inch for each foot of elevation, given, what is the greatest height that zone may extend below the valve?

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why D is correct

Using the stated 80 psi ceiling, the available static-pressure increase is 80 - 62 = 18 psi. Divide by 0.433 psi per foot to obtain a maximum drop of about 41.57 feet. The listed choice of about 41 feet stays below that limit; an actual design must not round the maximum upward. The 143-foot choice uses the valve setting alone, and the 185-foot choice uses the full 80 psi without subtracting the existing 62 psi. That latter method would give about 142 psi at the bottom, not more than twice 80 psi.