Iowa Admin. Code r. 875-92.10
This rule applies to power boilers installed prior to July 1, 1983. Each boiler shall have a pressure gage so located that the gage is readable. The pressure gage shall be installed so that it shall at all times indicate the pressure in the boiler Each steam boiler shall have the pressure gage connected to the steam space or to the water column or its steam connection. A valve or cock shall be placed in the gage connection adjacent to the gage. An additional valve or cock may be located near the boiler providing it is locked or sealed in the open position. No other shutoff valves shall be located between the gage and the boiler The pipe connection shall be of ample size and arranged so that it may be cleared by blowing out. For a steam boiler the gage or connection shall contain a siphon or equivalent device that will develop and maintain a water seal that will prevent steam from entering the gage tube. Pressure gage connections shall be suitable for the maximum allowable working pressure and temperature, but if the temperature exceeds 406° F, brass or copper pipe or tubing shall not be used. The connections to the boiler, except the siphon, if used, shall not be less than 1/4-inch standard pipe size, but where steel or wrought-iron pipe or tubing is used, they shall not be less than 1/2-inch inside diameter The minimum size of a siphon, if used, shall be 1/4-inch inside diameter. The dial of the pressure gage shall be graduated to approximately double the pressure at which the safety valve is set, but in no case to less than 11/2 times this pressure.
Iowa Admin. Code r. 875-92.10