When selecting industrial valves, one question often arises among engineers and plant operators — are trunnion ball valves bidirectional? The answer has a direct impact on flow control, system efficiency, and safety. Understanding whether a valve allows flow in both directions or only one is essential to choosing the right type for your application. In this article, we’ll explain what a trunnion ball valve is, what bidirectional and unidirectional flow mean, how trunnion mounted ball valves function, and why GOTEB trunnion ball valves are trusted worldwide for precision and reliability.
A trunnion ball valve is a type of ball valve where the ball is anchored by a mechanical support system at both the top and bottom — known as a trunnion.
The trunnion meaning refers to the pivoting shaft or extension that stabilizes the ball inside the valve body, preventing it from shifting under pressure.
Unlike floating ball valves, where the ball moves slightly to create a seal, trunnion mounted ball valves keep the ball fixed while the seats move toward it. This design reduces torque, improves sealing, and enhances durability, especially under high pressure or large-diameter conditions.
Valve Body: Encloses the ball and seats, built for high-pressure resistance.
Ball (Sphere): A precision-drilled sphere allowing or blocking flow.
Trunnion Shaft: Holds the ball steady during operation.
Seats: Spring-loaded components that ensure tight sealing.
Stem & Actuator: Control the ball valve open/close direction.
The trunnion ball valve design makes it ideal for industries like oil & gas, petrochemical, and power generation — where precision, pressure control, and reliability are paramount.
A bidirectional ball valve is one that can seal and control flow in both directions. This means fluid can enter from either side — upstream or downstream — without compromising the sealing performance.
Two-way sealing: The valve seals equally well in both directions.
Flexible installation: The valve can be installed without worrying about flow direction.
Higher safety margin: Even if system pressure reverses, the valve still maintains tight closure.
Bidirectional valves are widely used in systems where flow reversal is possible, such as multi-line process systems, storage terminals, or automated flow control loops.
A unidirectional ball valve is designed to seal effectively in only one direction. In such valves, pressure applied from the wrong side may cause seat deformation or leakage.
These valves are often used in:
High-pressure pipelines with fixed flow direction.
Systems requiring pressure relief in one direction.
Fire-safe or vented ball designs (where cavity pressure must escape in one direction).
Unidirectional valves typically have an arrow marking on the valve body, indicating the correct flow direction. Installing them incorrectly can lead to sealing failure — a key reason why understanding directionality is critical.
In most cases, trunnion mounted ball valves are bidirectional. Their structural design enables tight, reliable sealing from both sides of the valve. Let’s explore how this works.
Trunnion ball valves use dual spring-loaded seats positioned on both sides of the ball. These seats move slightly to press against the ball, forming a seal whenever pressure is applied — from either direction. Because both seats are independently spring-loaded, the valve maintains sealing integrity whether flow is upstream or downstream. This symmetrical structure makes the valve bidirectional by design.
Unlike floating ball valves (where the ball moves under pressure), trunnion mounted ball valves feature a fixed ball and movable seats. The trunnion — a mechanical shaft support — absorbs the pressure load, ensuring the ball remains stationary. This design reduces wear on seats, lowers operating torque, and guarantees consistent sealing performance, even under high-pressure and large-diameter conditions.
Both seats in a trunnion valve are designed to provide equal sealing strength.
No matter which side experiences pressure, the seats are pushed toward the ball to maintain a perfect seal. This is essential for critical flow systems where reverse pressure can occur during operation or maintenance.
Because the ball is supported at two points (top and bottom), trunnion mounted ball valves can withstand extreme conditions — including pressures up to 2500LB.
They are particularly suited for:
Oil & gas transmission lines
Petrochemical refineries
Offshore platforms
Power generation systems
The design ensures smooth operation, minimal torque, and zero leakage — even in high-temperature, high-pressure, or corrosive media environments.
Although most trunnion ball valves are bidirectional, there are certain specialized cases where they may function as unidirectional.
Single-Seat Design:
Some trunnion ball valves use a single-seat structure that seals only in one direction.
Vented Ball or Cavity Relief Design:
To prevent trapped pressure between the ball and body, some designs incorporate a pressure-relief vent — making them unidirectional for safety reasons.
Fire-Safe Valves (API 6D):
Certain fire-safe trunnion ball valves are designed to vent cavity pressure downstream to protect against fire damage, thus allowing sealing in only one direction.
Markings on Valve Body: Single arrow = unidirectional; double arrow = bidirectional.
Seat Configuration: Dual spring-loaded seats = bidirectional; single seat = unidirectional.
Manufacturer Data Sheet: Always refer to technical documents provided by trunnion ball valve manufacturers like GOTEB.
Most engineers prefer bidirectional trunnion ball valves because of their superior flexibility, safety, and installation convenience.
Simplified Installation: No need to align the valve with a specific flow direction.
Enhanced Safety: Maintains sealing even if system pressure reverses.
Reduced Inventory: One valve type can serve multiple system layouts.
Low Maintenance: Balanced pressure and low wear extend service life.
Reliable Operation: Consistent sealing in both flow directions under all conditions.
This is why industries handling critical fluids, gases, or hazardous materials often rely on GOTEB trunnion ball valves for guaranteed performance and durability.
So, are trunnion ball valves bidirectional?
Yes — most trunnion mounted ball valves are designed to be bidirectional, capable of sealing and controlling flow in both directions. Their dual-seat, spring-loaded structure, fixed ball support, and balanced design ensure reliable sealing even under fluctuating pressures or reverse flow.
However, always check for directional markings or seat configuration, as certain special-purpose valves (such as vented or fire-safe types) may be unidirectional.
GOTEB is a leading manufacturer of high-quality valve components, specializingin ball valve spheres and trunnion mounted ball valves.
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