155515 ⎘
Water-tube boilers of vertical or steeply-inclined type, i.e. the water-tube sets being arranged vertically or substantially vertically built-up from substantially straight water tubes involving a single upper drum and a single lower drum, e.g. the drums being arranged transversely the water tubes being arranged sectionally in groups or in banks, e.g. bent over at their ends the tubes being placed in layers