Iowa Admin. Code r. 875-92.12
This rule applies to power boilers installed prior to July 1, 1983. Each boiler shall have a blowoff pipe fitted with valve or cock, in direct connection with the lowest water space practicable.
When the maximum allowable working pressure exceeds 125 psig, the blowoff pipe shall be at least schedule 80 from the boiler to the valve or valves and shall run frill size without reducers or bushings. Galvanized materials shall not be used.
All fittings between the boiler and valve shall be steel or at least schedule 80 fittings of bronze, brass, malleable iron, or cast iron, all of which shall be suitable for the pressure and temperature. In case of replacement of pipe or fittings in the blowoff lines, as specified in this paragraph, they shall be installed in accordance with the rules of new installations.
When the maximum allowable working pressure exceeds 125 psig, each bottom blowoff pipe shall be fitted with at least a 250-pound standard valve or cock. Two valves, or a valve and a cock, should be used on each blowoff.
When exposed to direct furnace heat, a bottom blowoff pipe shall be protected by firebrick or other heat resisting material so arranged that the pipe may be inspected.
An opening in the boiler setting for a blowoff pipe shall be arranged to provide for free expansion and contraction.
Iowa Admin. Code r. 875-92.12