Valves are essential across numerous industries, with a wide range of materials available to suit different high-demand applications. Some common materials include PVC, carbon steel, stainless steel, cast iron, and ductile iron. In this post, we will focus on two of these: ductile iron and cast iron.
The debate over “ductile iron vs. cast iron valves” has persisted for decades, as many are unaware of their key differences. Fortunately, comparing these materials is straightforward, as they differ in only a few significant ways. Below, we’ll examine the properties of both materials and explore their advantages and disadvantages.
Cast Iron Valve Specifications
Cast iron valve, also known as gray ironvalve, has been used for centuries due to its durability and affordability. This alloy consists of 96%-98% iron, 2%-4% carbon, and small amounts of silicon. One of its standout features is its impressive temperature tolerance, with some cast iron capable of withstanding temperatures exceeding 2,100°F (1,150°C).
In terms of pressure capacity, cast iron strength varies by pressure class:
– Class 125 cast iron flanges are rated for 150-200 psi at moderate temperatures.
– Class 250 cast iron is more robust, handling pressures between 300-500 psi, depending on the end type.
Strengths and Limitations
Strengths:
– Durability – Resistant to intense vibrations, ensuring long-term reliability.
– Cost-Effective – One of the most economical metal options, making it ideal for budget-conscious buyers.
Limitations:
– Brittleness – Unlike ductile iron, cast iron lacks flexibility. Any significant bending can cause cracking, rendering it unusable.
Despite its fragility under stress, cast iron remains a popular choice for applications where cost-effectiveness and vibration resistance are key factors.
Ductile Iron Valve Specifications
Ductile iron is a modern iron alloy designed for improved flexibility and strength. Unlike cast iron, which is brittle, ductile iron contains nodule-shaped graphite, giving it exceptional ductility—allowing it to bend without breaking.
While its temperature tolerance is slightly lower than cast iron, ductile iron can still withstand high temperatures of up to 1,350°F (730°C). In terms of pressure ratings, ductile iron valves follow standard pressure classes:
– Class 150 – Maintains a reliable seal up to 250 psi at typical outdoor temperatures.
– Class 300 – Handles pressures as high as 640 psi, making it suitable for high-pressure applications.
Unlike cast iron, ductile iron does not break when it is bent, so it is more suited for high demand applications. Ductile iron is a strong and reliable material for pipes, fittings, and valves. One drawback is price. Ductile iron is typically more expensive than cast iron due to its more complicated chemical makeup. If your application requires a tougher material, however, you may need to spend a little more.
Ductile vs. Cast Iron Valves
Durability
Cast Iron: Cast iron is a strong and pressure-resistant material, outperforming most plastics in this regard. However, when subjected to pressures beyond its rated capacity, it may bend or crack. With virtually no ductility, cast iron is rigid and prone to breaking under stress. Additionally, it is susceptible to rust over time, making regular maintenance essential to prevent corrosion buildup.
Ductile Iron: Ductile iron also boasts excellent structural integrity, capable of withstanding high pressures and temperatures without significant deformation. Unlike cast iron, its ductile nature allows it to flex slightly, reducing the risk of cracking. While it is still prone to rust, it resists corrosion more effectively than cast iron.
Ease of Installation
Cast Iron: Cast iron provides multiple installation options, with flanged connections being the most common. While welding is possible, it is challenging and generally not recommended. Our cast iron valves come with flanged ends, making them suitable for both high- and low-pressure applications.
Ductile Iron: Due to its structural similarities to cast iron, ductile iron shares many of the same installation methods. Bolting with flanges remains the preferred approach, while welding is not advisable.
Price
Cast Iron: Cast iron valves are more cost-effective due to their simpler manufacturing process. If the additional benefits of ductile iron are not required for your application, cast iron offers a budget-friendly solution.
Ductile Iron: While ductile iron valves come at a higher cost, they provide enhanced durability, flexibility, and resistance to cracking, making them a superior choice in demanding environments.