Each steam boiler shall have one or more water gage glasses attached to the water column or boiler by means of valved fittings, with the lower fitting provided with a drain valve of the straightway type with opening not less than 1/4 inch diameter. Gage glass replacement shall be possible with the boiler under pressure. Transparent material other than glass may be used for the water gage if suitable for the pressure, temperature and corrosive conditions encountered in service.
N.Y. Comp. Codes R. & Regs. Tit. 12 §§ 4-5.7