Rad
The Rad model changes the crown stay layout from vertical (centre above) to a more radial pattern (right). This has been found to be beneficial on other boiler models including the 118 model (left). The change in stay layout improves load and stresses some distance from the fire box crown, possibly reducing the need for as many flexible stays in the side walls of the boiler.
The radial stay pattern allows the wrapper to provide better support to the fire box crown. This has a visible benefit to stresses in the wrapper shoulders and fire box crown. All of the stays in the Rad model are fixed but many have lower stress than the flexible stay equivalents in the Flex1 and Flex2 models.
This alternative crown stay layout reduces stresses in those stays, especially the ones further from the boiler centre line. The stresses in the side stays are also reduced to the point where all but the top two rows could be fixed rather than flexible.
