What type of fittings should be used for low pressure CO2 systems that are larger than 3 inches?

Using 1000 lb ductile iron or forged steel fittings for low pressure CO2 systems that are larger than 3 inches is the appropriate choice because these materials can withstand the specific pressure requirements and operational conditions associated with CO2 systems. Ductile iron and forged steel are known for their strength and durability, making them suitable for larger pipe sizes where higher mechanical integrity is needed.

In low pressure environments, while plastic fittings may seem appealing due to their lightweight nature and ease of installation, they typically lack the robustness necessary for larger systems and can be more prone to failure under certain stress conditions. Similarly, stainless steel type 316 fittings are often used for corrosive environments but may not be necessary or cost-effective for standard low pressure applications. Malleable iron fittings, while commonly used in various plumbing and HVAC applications, may not meet the pressure requirements for larger systems as effectively as the specified ductile iron or forged steel fittings.