Relief valves shall be connected to the top of boilers, with the spindle
vertical either directly to a tapped or flanged opening in the boiler, to a
fitting connected to the boiler by a close nipple, to a Y-base, to a valveless
water pipe between adjacent boilers, or to a valveless header connecting water
outlets on the same boiler. When a Y-base is used the inlet area shall be not
less than the combined outlet areas.
(2) When the size of the boiler requires a
relief valve larger than 4 1/2 inches diameter, 2 or more valves having the
required capacity shall be used. When 2 or more valves are used on a boiler,
they may be single, directly attached, or mounted on a Y-base.