When is the use of a cast iron valve body permissible?

The use of a cast iron valve body is not permissible on high temperature water boilers due to safety concerns associated with the material properties of cast iron. Cast iron is prone to cracking under conditions of thermal stress and pressure, especially when exposed to high temperatures and significant pressure variations present in such systems. High temperature water boilers operate typically at temperatures above 250°F and often at pressures higher than 150 psi.

Because of its brittleness, cast iron can fail under the stress conditions of high temperature and pressure, which can lead to catastrophic failures and safety hazards. Therefore, only materials designed to withstand such conditions, like forged steel or other alloys, are acceptable for use in high temperature water boiler applications. This regulation is put in place to ensure the safety and reliability of boiler operations.