Cast Iron, Ductile Iron, Bronze and Stainless Steel Valves: What’s The Difference?

Not all valves are built the same and there’s good reason for that. Knowing a few basic facts about the different materials will ultimately have long-term effects on your application’s capabilities. Cast iron, ductile iron, bronze and stainless steel are all similar metals but what stands each of these apart? We’ll assist you in choosing the best metal solution for your everyday valve application needs.

Cast Iron

Cast iron — a metal made from mostly iron with small amounts of carbon and silicone — is known for its tolerance to extreme temperatures. It can handle temperatures over 2,100 degrees Fahrenheit. It is a very strong metal and can usually go undamaged through situations of intense vibration; however, cast iron is extremely rigid and has a low resistance to bending. Almost any bending will cause the material to fracture or break completely. A big advantage to cast iron is the cost. It is a relatively inexpensive metal and a very economical and useful option for most situations.

Ductile Iron

Ductile iron, as its very name suggests, is more flexible than cast iron. It is an iron alloy made with nodule-shaped graphite crating a metal that has a little more room to bend without breaking or cracking. With the ability to flex, however, comes a lower overall temperature tolerance than cast iron and a slightly higher cost.

Valves built from ductile iron have excellent corrosion resistance and superb strength, making it a great choice for applications in which a tougher material is needed and in conditions where weathering is likely. Here at Flomatic all of our ductile iron valves are epoxy coated to protect the valves from long term erosion and corrosion in many different fields of application.


The use of bronze in plumbing systems dates back to the Roman Empire. Made primarily from copper and tin, this metal is both strong and malleable. It does not crack as easily as iron as it has high ductility. Bronze is also known for its high resistance to corrosion even against harsher fluids and those similar to seawater. However, the nature of the alloy causes it to have a somewhat rough and porous surface which can leave the material susceptible to pitting and degradation over time if not properly maintained.

It is important to note that consumers should seek out valves with the lowest lead content. Make sure if you’re picking out a bronze valve for potable water, you’re choosing a valve that is ANSI/NSF 372 & ANSI/NSF 61 certified. These certifications mean it meets the minimum lead requirements for safe and healthy drinking water.

Stainless Steel

Stainless steel has become a very popular valve material for many reasons. Valves made from this metal have exceptionally high oxidation and corrosion resistance and extreme durability, making a product that lasts a long time. Stainless steel valves do not rust, even if placed in areas of high moisture or directly in water. This property makes them a great choice for coastal regions where saltwater corrosion may be a concern.

The smooth metal is easily cleaned, and a popular choice for food and beverage applications. Stainless steel has good heat resistance; however, it is not ideal for extreme high-temperature applications. A potential downside of stainless-steel valves is that they’re very expensive. However, with price, comes high-quality.

What do these terms all mean?

Using the information provided above, think about your scenario and the conditions in which the valve will be used. Will it be outdoors? In severe temperature? Will this metal be susceptible to movement and vibration? Once you determine the extremes, you’re easily able to choose the appropriate metal for your application.

And of course, never be afraid to ask the experts. With over 85 years of industrial experience in the valve market, Flomatic knows valves inside and out and we are happy to guide you to the right product for the right application.