The most common FDC colors and (a great NYC hometown thing) what do colors tell you?
Green Caps indicates that the FDC supplies the fire sprinkler system exclusively.
Red Caps indicates that the FDC supplies the standpipe exclusively.
Yellow Caps indicates that the FDC supplies both the fire sprinkler and the standpipe.

On the assigned day, a team of testers from Citywide will prepare the system and hook up a hydrostatic pump to the FDC ad pump high-pressure water into the system. The pump will be disconnected, and a compound gauge installed for the test marked or photo was taken for later inspection. (for up to two hours).

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