What type of pressure must Cast Iron boilers not exceed?

In determining the maximum pressure for Cast Iron boilers, it's important to recognize that these types of boilers are typically designed for lower pressure applications due to the material properties of cast iron, which can be prone to cracking under excessive stress. The limit of over 100 kPa is a safety measure based on the structural integrity of cast iron. Exceeding this pressure could compromise the safety and effectiveness of the boiler, potentially leading to failures or hazardous conditions.

Other pressure limits, such as those greater than 70 kPa or 150 kPa, do not align with the common standards and safety practices established for cast iron boilers. These standards are in place to ensure safe operation and longevity of the equipment, reflecting the inherent limitations of cast iron under too much internal pressure. Hence, the correct answer emphasizes the critical importance of adhering to the specified pressure limits for safe operation of cast iron boilers.