page_title: Yarrow boiler
section_title: Water drums
hierarchical_section_title: Yarrow boiler / Description / Later evolution in design / Water drums
caption_attribution_description: Straight watertube marine boiler (Rankin Kennedy, Modern Engines, Vol VI).jpgStraight Tube Marine Boiler
context_page_description: Yarrow boilers are an important class of high-pressure water-tube boilers. They were developed by
  Yarrow & Co., Shipbuilders and Engineers and were widely used on ships, particularly warships.
  The Yarrow boiler design is characteristic of the three-drum boiler: two banks of straight water-tubes are arranged in a triangular row with a single furnace between them. A single steam drum is mounted at the top between them, with smaller water drums at the base of each bank. Circulation, both upwards and downwards, occurs within this same tube bank. The Yarrow's distinctive features were the use of straight tubes and also circulation in both directions taking place entirely within the tube bank, rather than using external downcomers.
context_section_description: The first Yarrow water drums or "troughs" were D-shaped with a flat tubeplate, so as to provide an easy mounting for the tubes. The tubeplate was bolted to the trough and could be dismantled for maintenance and tube cleaning.
  This D shape is not ideal for a pressure drum though, as pressure will tend to distort it into a more circular section. Experience of boiler explosions had shown that sharp internal corners inside boilers were also prone to erosion by grooving.
  Later boilers used a more rounded section, despite the difficulty of inserting and sealing the tube ends when they were no longer perpendicular. These later drums had a manhole in the ends for access.
caption: Early Yarrow boiler, showing the D-shaped water troughs
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