Intro4u2u

Gate valves are manufactured in virtually every metal from Aluminum to Zirconium. They are also manufactured in a variety of engineering plastics. The most common materials however, are steel, iron and bronze.

Bronze offers the greatest machinability and the lowest manufacturing cost. The features that make bronze easy to machine, its lower strength and softness, also make the valve only suitable for lower pressure applications. The predominant service for bronze valves is on water and utility lines where pressures are lower than about 300 psi.

Iron valves are in between bronze and steel as far as strength goes. The iron is slightly harder to machine, but the iron castings are relatively easy to pour. Iron for valves is commonly two types; grey or cast iron and malleable iron. In refinery and petrochemical service iron valves are usually restricted to low pressure water lines. The high carbon content and better rust resistance of iron valves makes them more suitable for buried service than steel valves.

For industrial valves, steel is the material of choice. A broad spectrum of steels are utilized for valve construction, from the lowest grade WCB, to the chrome/moly’s. Unlike the brasses, bronzes and irons, most steels and low alloys are readily weldable, which makes them easier to modify, repair and in some cases even easier to manufacture. Gate valves are also manufactured in a number of exotic alloys from Titanium to Zirconium.

There have been several attempts to make the gate valve obsolete and take away its market share, but they have only met with limited success. The first challenger to the gate valve throne was the ball valve, which came into prominence during the middle part of the 20th century. Ball valves have been substituted for gate valves in many lower pressure and lower temperature applications, but in some cases they are more expensive to manufacture and repair. The elastomer seats of the ball valve also limit them to temperatures below about 500 degrees F.

Butterfly valves have supplanted gate valves in some of the larger (48” and above) low pressure applications, such as water works usage. The metal-seated butterfly valve has also been successful in certain critical service applications that once were solely the realm of the gate valve, but their high initial cost and very high repair costs make them unlikely to ever completely replace the venerable gate valve.