boiler stay#rod stay
A boiler stay is an internal structural element of a boiler. Where the shell of a boiler or other pressure vessel is made of cylindrical or (part) spherical elements, the internal pressure will be contained without distortion. However, flat surfaces of any significant size will distort under pressure, tending to bulge.{{cite book | title=Locomotive Management | last1=Hodgson | first1=Jas. T. | last2=Lake| first2=Chas. S. |year=1954 |edition=10th |publisher=Tothill Press |location=London |page=77}}
Types
Stays of various types are used to support these surfaces by tying them together to resist pressure. Some boiler configurations require a great deal of staying.{{Cite web |title=What is a Combi Boiler? Comparison Between Various Combi Boilers |url=https://theedinburghboilercompany.com/boilers/combi-boilers/ |access-date=2024-02-20 |language=en-US}} A large locomotive boiler may require several thousand stays to support the firebox. In water tube boilers, stays were sometimes used between their main chambers, and could themselves be water tubes.{{cite book |last=Robertson |first=L.S. |title=Water-Tube Boilers: Based on a Short Course of Lectures Delivered at University College, London |location=London |publisher=Murray |year=1901 |url=https://archive.org/stream/watertubeboiler02robegoog#page/n6/mode/2up |oclc=5640870 |pages=153–4}} A knuckle joint is used for diagonal stays in a boiler.
A cylindrical firebox may be self-supporting without stays because of its shape.
Gallery
File:Screwed boiler stay (Bentley, Sketches of Engine and Machine Details).jpg|Rod stay
File:Girder boiler stay (Bentley, Sketches of Engine and Machine Details).jpg|Girder stay
File:Longitudinal boiler stay (Bentley, Sketches of Engine and Machine Details).jpg|Longitudinal stay
File:Boiler gusset stay (Heat Engines, 1913).jpg|Gusset stay