What is the maximum pressure rating when using standard weight pattern malleable iron fittings that...

Standard weight pattern malleable iron fittings that are 6 inches in size and smaller typically have a maximum pressure rating of 300 psi (21 bar). This rating ensures that the fittings can withstand the pressure demands of most fire sprinkler systems without failure.

References: Fitting manufacturers provide specifications for malleable iron fittings, including their pressure ratings, which must comply with standards such as those set forth by ASTM and ANSI.