I have a system that was originally designed with a fire pump taking suction 
from an elevated municipal water tank.  At some point in time the system source 
was changed from the tank to a municipal water supply.  This change has 
resulted in the system pressures being well over 200-250 psi.  So far nothing 
has blown out, yet but numerous buildings and underground were built based on 
standard pressure rated components.

The thought for the day is this, when you run a calculation, the output will 
show the minimum required pressure at the hydraulically most remote sprinkler 
that is required to provide the design flow rate.  The calculations also show 
the deviation between Required and Available system pressures.  So, when the 
fire pump kicks on, what the system ACTUALLY sees is the rated pressure of the 
pump being introduced into the system, not the minimum required pressure that 
is shown in the calculations, Agreed?

If it is stated that in the calculations that the pressure at the sprinklers on 
an upper floor will be less than 175 psi but those on the lower floor will be 
greater is it safe to assume based on the ACTUAL pressures coming out of the 
pump that the entire system will likely see pressures exceeding 175 psi?

Looking for some thoughts.

Craig Prahl | Jacobs | Group Lead – Fire Protection | 864.676.5252 | 
[email protected] | www.jacobs.com<http://www.jacobs.com/>


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