Why are no stays used in the heads of a water tube boiler?

In a water tube boiler, the head, which is the end part of the boiler where water and steam gather, is designed to efficiently withstand the high pressures inside the system. The shaping of the head is typically done using a die, which helps to strengthen the material and allows it to handle the stresses placed on it during operation. This engineered shape eliminates the need for stays, which are structural supports typically used in other types of boilers, such as fire tube boilers, to hold unbraced surfaces in place under pressure.

Water tube boilers inherently have a design that favors high pressure and temperatures, which allows the pressure containment to be managed by the strength and shape of the heads. This efficient design reduces the risk of structural failure while eliminating additional components that would be necessary if stays were used. Thus, using a shaped head that can withstand pressure is both a practical and efficient solution in water tube boiler design.