In a standpipe system, what is the hydraulic calculation for the standpipe serving the stairwell?

• A. 500 gpm below node H
• B. 400 gpm above node F
• C. 600 gpm at the main riser
• D. 350 gpm at the base

Answer: (A)

In hydraulic calculations for standpipe systems, you determine the flow in each segment by the demand of the outlets that segment serves, accounting for friction losses and elevation. The standpipe that feeds the stairwell is supplied by a specific branch, and the flow in that branch must meet the standpipe’s demand. Here, the branch feeding the stairwell is designed to carry 500 gpm, so the hydraulic calculation for that standpipe is 500 gpm at the point just below the node where that branch ties into the rest of the system (below node H). This location reflects the actual flow entering the standpipe and the losses along the path to its outlets, making it the hydraulically controlling point for the stairwell standpipe. Flows measured at other segments (above other nodes or at the base) do not represent this branch’s demand and aren’t the correct calculation for the stairwell standpipe.