For a smaller-bore or lower-pressure application, a floating ball valve is often a practical, compact choice. For larger sizes, higher differential pressures, or frequent operation, a trunnion-mounted design may be a better fit because its supported ball can reduce the load transferred to the seats and operating mechanism. Neither type is universally superior: the right choice depends on valve size, pressure and temperature conditions, operating frequency, shutoff requirements, and total installed cost.
Both designs use a ball with a bore that turns to control flow. In a typical quarter-turn arrangement, the ball rotates 90 degrees between open and closed positions. The key difference is how the ball is supported and how the seats create a seal.
A floating ball is held in position by the stem and seats, but it can move slightly downstream when pressure acts on it. That movement pushes the ball against the downstream seat to help achieve shutoff. In a trunnion ball valve, the ball is supported by fixed upper and lower bearings or trunnions, while the seats move toward the ball to create sealing contact.
The ball in a floating design is not fixed by trunnions. The stem turns the ball, and under pressure the ball can shift slightly toward the downstream seat. This pressure-assisted contact can support shutoff, but it also places load on the seats and valve components.
As pressure, valve size, and operating conditions change, the forces on the ball and seats change as well. A floating design can be an effective solution when the selected product is rated for the service conditions. Buyers should not assume that all floating valves have the same pressure capability or torque requirements.
A trunnion-mounted ball is supported by bearings or trunnions, which limit its movement under line pressure. The seats move toward the ball to maintain sealing contact. Because the ball is supported, the seats generally carry less of the ball’s pressure-induced load than in a comparable floating arrangement.
This support can help manage operating torque, particularly as valve size or differential pressure increases. Actual torque still depends on factors such as seat material, pressure, temperature, lubrication, design, and operating frequency. Buyers should request the manufacturer’s torque data for the specified service rather than relying on a design label alone.
| Comparison point | Floating ball valve | Trunnion ball valve |
|---|---|---|
| Ball support | Ball can shift under pressure and load the downstream seat. | Ball is supported by trunnions or bearings; seats move toward the ball. |
| Seat loading | Pressure-assisted sealing involves force transferred through the ball to the seat. | Ball support can reduce the pressure-induced load carried by the seats. |
| Operating torque | Can increase with size and differential pressure; verify product-specific data. | May be lower for comparable demanding conditions, but depends on the design and service. |
| Construction and sourcing | Often simpler in construction and may offer a lower initial purchase cost. | Typically has additional support components and may cost more; compare total project cost. |
| Selection priority | Suitability within the valve’s stated size and pressure-temperature envelope. | Support, torque, and duty requirements for the specified operating conditions. |
Use the table as an initial screening tool, not as a substitute for a datasheet. Pressure class alone does not establish suitability across all temperatures, materials, seat configurations, or operating conditions. Ask suppliers to confirm the complete rating for the exact valve configuration and service.
A floating valve may suit general isolation duties where the required bore, pressure, temperature, and cycle frequency fall within the manufacturer’s limits. Its simpler construction can make it attractive for projects that need a straightforward shutoff valve and are sensitive to upfront cost. The decision should still account for the operating torque and expected seat life under the actual service conditions.
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For example, a buyer evaluating a 2 in (DN 50) line can use that size as an initial comparison point, but the nominal size alone does not determine the appropriate design. The buyer also needs to establish the maximum differential pressure across the closed valve, the operating temperature, and whether the valve will be cycled regularly. The manufacturer’s sizing and rating information should resolve whether a floating model is suitable.
A trunnion valve is worth evaluating when a project involves a larger bore, high pressure or differential pressure, frequent operation, or actuator torque limits. The supported ball can help manage pressure-induced loads, which may be important when selecting manual or automated operation. The project team should compare the specified torque, actuator requirements, and maintenance expectations for both designs.
For either type, define the full operating envelope rather than using only the normal operating point. Include maximum and minimum pressure and temperature, the fluid composition, flow direction, and required shutoff performance. If the application requires specific features such as cavity relief or double-block-and-bleed capability, confirm those features in the selected valve design; they are not guaranteed simply by choosing a trunnion valve.
Floating valves may have a lower initial price when their design meets the service requirements, while trunnion valves can involve more components and a higher purchase cost. However, comparing purchase prices alone can hide costs associated with actuation, maintenance, replacement intervals, or an unsuitable selection. Ask suppliers to quote the same materials, ends, pressure rating, testing requirements, and accessories so the comparison is meaningful.
Lead time varies with size, materials, pressure class, configuration, production capacity, and inspection requirements. Custom materials or non-standard end connections may affect both schedule and price for either design. For time-sensitive projects, confirm the delivery schedule and required documentation against the exact bill of materials before placing an order.
A common mistake is choosing a valve based only on nominal size or pressure class. Another is assuming that a trunnion design automatically provides a particular leakage rate, cavity-relief behavior, or block-and-bleed function. These details depend on the product’s construction and specified testing, so buyers should obtain written confirmation.
It is also risky to select an actuator before confirming valve torque for the actual operating conditions. If the service includes temperature extremes, unusual fluids, or frequent cycling, share those details during quotation rather than treating them as later additions. A complete technical review helps prevent mismatched equipment and avoidable procurement changes.
Floating and trunnion ball valves both provide quarter-turn isolation, but their ball-support and seat-loading arrangements differ. A floating valve is often a sensible option when the specified service fits its rated envelope and simplicity or initial cost is important. A trunnion valve is often worth considering when size, differential pressure, operating frequency, or torque requirements make supported-ball construction advantageous.
As 凯维 (KEWEI), we recommend beginning with the application data and comparing complete, rated configurations rather than selecting by valve type alone. Share your line size, pressure and temperature range, medium, connection type, operating frequency, and required documentation with our team. We can help assess the appropriate design and prepare a quotation for your project requirements.
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