In an industrial valve it is not enough to define the type of obturator or the pressure class. The choice of materials for the body and the seats determines how the valve will respond to the fluid, the environment, and the passage of time. This decision directly affects resistance to corrosion and wear, the level of tightness that can be achieved, and the frequency with which intervention in the installation will be required.
From an engineering perspective, selecting the right materials means aligning three factors: service conditions, resistance to corrosion and erosion, and the degree of sealing required at the service point. With pressure, temperature, type of medium, and the presence of solids clearly defined, it is possible to determine whether the body should prioritize environmental resistance, whether the seat must withstand severe service, or whether the priority is tight shut-off at low pressure.
Bronze: valve body for aggressive environments
The valve body is the component that bears the mechanical load and is continuously exposed to the surrounding environment. Bronze offers high resistance to corrosion, wear, and even to the action of non-oxidizing acids. This combination of properties makes it an ideal material for hydraulic equipment and, in particular, for valves that operate for long periods under demanding low-pressure conditions.
Bronze does not rust, as it contains a negligible amount of iron. For this reason, it is the optimal material for valves used in aggressive environments such as seawater, where many alloys degrade rapidly. This characteristic explains the high demand for bronze valves in the marine sector, in addition to their non-magnetic nature.
The main sectors demanding FHT bronze valves are marine, petrochemical, sanitation, and industrial applications. The nobility of this alloy allows its use to be extended to fields such as nuclear, offshore, or energy when a robust solution against environmental corrosion is required. Choosing bronze as a body material is a direct way to protect the installation from aggressive environmental conditions.
Metal-to-metal seats: mechanical strength and severe service
The seats are responsible for closing the valve. In a floating ball valve, the ball, connected to a shaft at the top, rotates ninety degrees and the pressure of the flow pushes it against the downstream seat, creating the seal. The seat material defines the service range within which this closure is maintained.
Metal seats are suitable for corrosive environments and products, for high temperatures, and for fluids containing suspended particles. Depending on the material, metal-to-metal seated valves can withstand more severe conditions than soft-seated valves, including acids, heat, abrasives, water hammer, erosion, and high pressure.
This capability comes at a cost. Metal-seated ball valves generally cost more than soft-seated valves and, by design, may exhibit more leakage over the long term than an equivalent soft-seat solution. In very low-pressure applications, once some seat wear has occurred, there may not be sufficient pressure to keep the ball pressed against the downstream seat and ensure a completely tight shut-off. From a materials standpoint, choosing metal-to-metal seats means prioritizing thermal, chemical, and mechanical resistance over maximum tightness at low pressure.
Thermoplastic soft seats: tight shut-off and operating torque
When the main requirement is sealing performance and control stability, the choice shifts toward thermoplastic soft seats. In guided (trunnion-mounted) ball valves, the ball is anchored by a second shaft at the bottom—the trunnion—which prevents axial movement and allows adequate sealing on both sides. This configuration is particularly suitable for three- or four-way valves and very low-pressure applications.
In these valves, the sealing surfaces are made from non-metallic thermoplastic materials such as PTFE, Nylon, DEVLON, or PEEK. These seats operate at service temperatures below two hundred seventy degrees Celsius, depending on the sealing material. Under appropriate conditions, soft-seated valves can offer a very high level of sealing throughout their service life, typically higher than that of a conventional metal valve. In addition, they require less operating torque than floating ball valves, which simplifies automation.
The limitation is set by the thermoplastic material itself. Soft-seated ball valves are not well suited for highly corrosive media or for dirty or abrasive process fluids, as these conditions can damage the seat and cause leakage. They also do not withstand the same pressure levels as metal-seated valves. In return, within their service window they offer high tightness at a competitive cost.
Combining materials according to process specification
Selecting materials for an industrial valve involves combining body and seats in a way that is consistent with the process specification. In aggressive environments, a bronze body provides resistance to corrosion and wear. At severe service points with high temperature, particles, and corrosive media, metal-to-metal seats maintain closure under demanding conditions. When the service point requires very high sealing performance with low operating torque and good response at low pressure, thermoplastic soft seats in guided ball valves offer an effective solution.
Based on service conditions and fluid type, FHT Valves can help determine which combination of bronze, metal-to-metal seats, or soft seats is best suited to meet the control, safety, and service life objectives of each installation.