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Introduction
In industrial piping systems, ball valves are widely used in various fluid control systems due to their compact structure, fast opening and closing, low flow resistance, and good sealing performance.When selecting a ball valve, we often come across two types: floating ball valves and trunnion-mounted ball valves.Since both types open and close by rotating the ball 90°, why are they designed with two different structures?The key difference is not simply whether the ball can move, but how the two structures handle media pressure loads, seat sealing loads, and operating torque.This article focuses on the core differences between floating ball valves and trunnion-mounted ball valves, why both structures are needed in engineering, and how to choose between them in actual projects.
Quick Answer
The fundamental reason ball valves are divided into floating ball valves and trunnion-mounted ball valves is that the two structures handle media pressure loads, seat sealing loads, and operating torque differently.In a floating ball valve, the ball can move slightly in the direction of flow under media pressure and press against the downstream seat to create a seal. Its structure is relatively simple, so it is commonly used in small- and medium-sized industrial pipelines within suitable pressure ratings.A trunnion-mounted ball valve, on the other hand, uses a support structure to restrict axial movement of the ball. The movable seats are pressed against the ball by preload and media pressure to form the seal. This structure is advantageous in large-diameter, high-differential-pressure systems and applications where operating torque control is important, because it helps manage the loads acting on the ball and seats.However, this does not mean that “floating ball valves can only be used for low pressure” or that “trunnion-mounted ball valves must always be used for high pressure.” Actual selection still depends on valve size, pressure rating, maximum differential pressure, materials, seat design, sealing requirements, and operating torque.
Table of Contents
- What Is the Core Difference Between Floating Ball Valves and Trunnion-Mounted Ball Valves?
- Why Are Both Floating Ball and Trunnion-Mounted Ball Structures Needed?
- Floating Ball Valve vs Trunnion-Mounted Ball Valve: Main Differences
- How Should You Choose in an Actual Project?
- FAQ
Keywords: ball valve, floating ball valve, trunnion-mounted ball valve, difference between floating ball valve and trunnion-mounted ball valve, industrial ball valve
You can quickly learn more by watching the following videos:
1. What Is the Core Difference Between Floating Ball Valves and Trunnion-Mounted Ball Valves?
The most obvious difference between the two types of ball valves lies in how the ball is supported and how the valve creates a seal.
1.1 Floating Ball Valve: The Ball Moves Slightly
The ball in a floating ball valve is not completely restricted from axial movement by upper and lower support structures.
When the valve is closed, a pressure difference forms between the upstream and downstream sides. Media pressure acts on the ball, causing it to move slightly in the direction of flow and press against the downstream seat, thereby forming a seal.
The sealing process can be simply understood as:
Media pressure → pushes the ball → ball presses against the downstream seat → sealing is achieved
Therefore, media pressure itself is also an important source of sealing force in a floating ball valve.
Main Features of Floating Ball Valves
- Relatively simple structure
- Fewer components
- Compact valve body structure
- Relatively lower manufacturing cost
- Relatively easy maintenance
- Commonly used in small- and medium-sized applications
- Can provide good sealing performance with a suitable seat design
It should be noted that a floating ball valve does not necessarily mean it can only be used in low-pressure applications.
Some specially designed small-size floating ball valves can also cover relatively high pressure ratings. The allowable pressure range depends on valve size, material, seat design, sealing material, structural design, and applicable standards. Therefore, the specific product model and technical data should always be used as the basis for selection.
1.2 Trunnion-Mounted Ball Valve: The Ball Is Supported and the Seat Moves Toward the Ball
The ball in a trunnion-mounted ball valve is supported by a structure that restricts axial movement.
Under pipeline pressure, the ball mainly remains in a fixed position while rotating, rather than moving noticeably downstream as it does in a floating ball valve.
So how does it achieve sealing?
The key lies in the movable seat.
Trunnion-mounted ball valves usually use a seat structure with preload. When the valve is closed, the seat is pressed against the ball by spring preload and media pressure, thereby forming a seal.
This can be simply understood as: the ball remains fixed → media pressure and preload act on the seat → the seat presses against the ball → sealing is achieved
Therefore, the two structures can be summarized in one sentence: in a floating ball valve, “the ball finds the seat,” while in a trunnion-mounted ball valve, “the seat finds the ball.”
This is also the simplest way to understand how the two types work.
2. Why Are Both Floating Ball and Trunnion-Mounted Ball Structures Needed?
The real reason ball valves need two different structures is not their names, but how pressure loads act on the ball and seats, and how these loads ultimately affect sealing performance and operating torque.
2.1 Pipeline Differential Pressure Creates Load on the Ball in the Closed Position
When a ball valve is closed, there is usually a pressure difference between the upstream and downstream sides.
Media pressure acts on the effective area of the ball, creating a load in the direction of flow.
For a floating ball valve, this load pushes the ball toward the downstream seat.
For small- and medium-sized valves under suitable pressure conditions, this design is simple and can use media pressure to enhance sealing between the ball and downstream seat.
However, when the valve size increases or the shutoff differential pressure becomes higher, the load acting on the ball also increases.
This is where the differences between the two ball valve structures become more obvious.
2.2 As Size and Differential Pressure Increase, Downstream Seat Load Also Increases
In a floating ball valve, after the ball is subjected to media pressure, the corresponding load is transferred to the downstream seat.
Therefore, under otherwise similar conditions:
Larger size or higher shutoff differential pressure → greater load on the ball → greater load on the downstream seat
This does not mean that floating ball valves cannot be used at relatively high pressures. It means that as size and differential pressure increase, the ball, seats, and related sealing structures must withstand greater loads.
At this point, seat material, structural design, sealing method, and valve size become increasingly important.
2.3 Increased Seat Load Further Affects Friction and Operating Torque
There is not only sealing force between the ball and seat, but also friction.
When a floating ball valve is closed, media pressure pushes the ball against the downstream seat. As differential pressure and valve size increase, the contact load between the ball and seat may increase, and the corresponding friction may also increase.
When the valve is reopened, the stem and actuator must overcome this friction.
Therefore, under otherwise similar conditions: the larger the valve size and the higher the shutoff differential pressure, the greater the operating torque required by a floating ball valve may become.
For manually operated ball valves, operation may become more difficult.
If the valve is equipped with:
- Pneumatic actuator
- Electric actuator
- Hydraulic actuator
the actuator must provide sufficient output torque while also taking an appropriate safety factor into account.
Therefore, valve torque does not only affect operating convenience. It also directly affects actuator sizing, system dimensions, and automation configuration costs.
2.4 How Does the Trunnion-Mounted Structure Manage Ball and Seat Loads?
A trunnion-mounted ball valve uses a support structure to support the ball, so that under pressure the ball does not rely on overall downstream movement to achieve sealing.
Part of the load generated by the media is carried by the ball support structure, while sealing is mainly achieved by movable seats pressing against the ball.
Therefore, under large-diameter and relatively high differential pressure conditions, the trunnion-mounted structure can manage the following more effectively:
- Ball load
- Seat load
- Friction between the ball and seats
- Valve operating torque
The trunnion-mounted structure can effectively reduce the problems caused by increased ball load, seat load, and operating torque under large-diameter and high-differential-pressure conditions. Therefore, it offers clear structural advantages in these applications.
2.5 Why Not Use Trunnion-Mounted Ball Valves for Everything?
If trunnion-mounted ball valves have advantages under large-diameter and high-differential-pressure conditions, why not use this structure for all ball valves?
Because the structure of a trunnion-mounted ball valve is usually more complex.
It may generally require additional components such as:
- Ball support structure
- Lower support shaft or trunnion
- Bearings
- Movable seats
- Spring preload mechanism
- Additional sealing and support components
This means its design, machining, and assembly are more complex, and the manufacturing cost is usually higher.
By comparison, for small- and medium-sized valves and general industrial applications, if a floating ball valve can already meet the required pressure, sealing, and operating torque requirements, the simpler floating ball structure usually offers better cost effectiveness.
Therefore, floating ball valves and trunnion-mounted ball valves are not about which one is “more advanced.” They are two engineering solutions designed for different load conditions.
3. Floating Ball Valve vs Trunnion-Mounted Ball Valve: Main Differences
| Comparison Item | Floating Ball Valve | Trunnion-Mounted Ball Valve |
|---|---|---|
| Ball Structure | The ball can move slightly in the direction of flow | The ball is supported by a structure that restricts axial movement |
| Sealing Principle | Media pressure pushes the ball against the downstream seat | The seat is pressed against the ball by preload and media pressure |
| Ball Movement | Rotates and can also move slightly | Mainly rotates |
| Differential Pressure Load Handling | Media pressure pushes the ball and transfers the load to the downstream seat | The ball load is mainly carried by the support structure, while the seat moves toward the ball to create the seal |
| Effect of Increasing Size / Differential Pressure | Downstream seat load and opening torque may increase significantly | Better suited to managing ball loads under large-size and relatively high differential pressure conditions |
| Seat Structure | Relatively simple | Usually uses movable seats with preload |
| Operating Torque | May increase significantly as size and differential pressure increase | Usually easier to control under large-diameter and high-differential-pressure conditions |
| Structural Complexity | Relatively simple | Relatively complex |
| Manufacturing Cost | Relatively lower | Relatively higher |
| Common Sizes | More common in small- and medium-sized valves | More common in medium- and large-sized valves |
| Maintenance | Fewer parts and relatively easier maintenance | More components and relatively higher maintenance requirements |
The most important point in this table is not simply to remember that “floating ball valves are suitable for small sizes and trunnion-mounted ball valves are suitable for large sizes,” but to understand the logic behind it: the real difference lies in how the two structures handle ball loads, seat loads, and operating torque caused by differential pressure.
4. How Should You Choose in an Actual Project?
In actual valve selection, it is not recommended to make a decision based only on whether the pressure is “high” or the valve size is “large.” The following parameters should be considered together.
4.1 Valve Size
For general small- and medium-sized pipelines, if pressure, seat load, and operating torque all meet the design requirements, floating ball valves usually offer the advantages of a simple structure and better economy.
As valve size increases, the effective pressure area of the ball increases, and the load applied by the media to the ball may also increase.
Therefore, for medium- and large-sized ball valves, the trunnion-mounted structure should be carefully evaluated.
4.2 Maximum Working Pressure and Shutoff Differential Pressure
When selecting a ball valve, the maximum system working pressure should not be the only consideration.
Special attention should also be paid to:
The maximum differential pressure the valve may experience when closed.
This is because one of the important factors affecting ball load, seat load, and operating torque is the pressure difference across the ball in the closed position.
Therefore, even if two projects have the same working pressure rating, different shutoff differential pressures may result in different requirements for the ball valve structure and actuator torque.
4.3 Seat Load and Operating Torque
For automated ball valves, operating torque is a very important parameter.
If the valve is to be equipped with a pneumatic, electric, or hydraulic actuator, the following should be confirmed according to the actual operating conditions:
- Opening torque
- Closing torque
- Torque at maximum differential pressure
- Seat friction
- Actuator output torque
- Safety factor
Especially under large-diameter or high-differential-pressure conditions, the trunnion-mounted structure is usually more favorable for controlling ball and seat loads, making actuator sizing more reasonable.
4.4 Sealing Structure and Project Requirements
In actual projects, in addition to deciding whether the ball is floating or trunnion-mounted, the seat and sealing design must also be further confirmed.
Especially for trunnion-mounted ball valves, different projects may have requirements for the following functions:
- Seat pressure relief
- Bidirectional sealing
- Bidirectional isolation
- DBB
- DIB
- Leakage class
- Fire-safe design
Therefore, all sealing functions cannot be determined simply from the term “trunnion-mounted ball valve.”
The actual sealing and pressure management capabilities of a trunnion-mounted ball valve still need to be confirmed according to the specific seat structure and project specifications.
Valve operating frequency can also be considered here. If frequent operation is required, additional attention should be paid to seat wear, ball surface treatment, operating torque, and valve service life, rather than simply assuming that “frequent operation always requires a trunnion-mounted ball valve.”
4.5 Life-Cycle Cost
Ball valve selection should not be based only on purchase price.
Floating ball valves have a simple structure, so their initial purchase cost is usually lower.
Trunnion-mounted ball valves have a more complex structure and usually a higher initial cost. However, for large-diameter, high-differential-pressure, or critical automated pipelines, the trunnion-mounted structure may be more suitable for long-term operation in terms of load management, operating torque, and actuator matching.
Therefore, the following should be considered together:
Purchase cost + actuator cost + maintenance cost + service life + system reliability
rather than comparing only the price of a single valve.
Quick Selection Reference
| Operating Condition | Recommended Focus |
|---|---|
| Small- and medium-sized valve + load and torque requirements are satisfied | A floating ball valve can be evaluated |
| Large size + relatively high shutoff differential pressure | Focus on evaluating a trunnion-mounted ball valve |
| High pressure + small size | Do not directly rule out a floating ball valve; evaluate according to the specific model |
| High requirements for operating torque control | Focus on comparing trunnion-mounted structures |
| Special requirements for seat pressure relief, bidirectional isolation, DBB / DIB, etc. | Further confirm the specific seat structure of the trunnion-mounted ball valve |
This method of classification by operating condition is more accurate than simply distinguishing the two ball valve types by industries such as petroleum, chemical processing, or water treatment, because both floating ball valves and trunnion-mounted ball valves may be used in the same industry or even within the same plant or system.
KST Ball Valve Selection Recommendations
KST provides both floating ball valves and trunnion-mounted ball valves. Actual selection should be confirmed according to valve size, media, working pressure, maximum differential pressure, temperature, material, and control method.
When making an inquiry or technical confirmation, it is recommended to provide the following parameters:
- Media
- Valve size
- Working temperature
- Normal working pressure
- Maximum working pressure
- Maximum shutoff differential pressure
- Valve body material
- Seat material
- Connection standard
- Pressure rating
- Actuation method
- Leakage requirements
These parameters are more helpful for confirming the appropriate valve structure and configuration than simply stating “a floating ball valve is required” or “a trunnion-mounted ball valve is required.”
5. FAQ
1. What Is the Biggest Difference Between a Floating Ball Valve and a Trunnion-Mounted Ball Valve?
The biggest difference lies in how the ball is supported and how the sealing load is handled.
The ball in a floating ball valve can move slightly under media pressure and presses against the downstream seat to create a seal.
The ball in a trunnion-mounted ball valve is restricted from axial movement by a support structure, and sealing is mainly achieved by movable seats pressing against the ball under preload and media pressure.
In simple terms: in a floating ball valve, “the ball finds the seat,” while in a trunnion-mounted ball valve, “the seat finds the ball.”
2. Why Are Trunnion-Mounted Ball Valves More Commonly Used for Large Sizes?
As valve size increases, the effective pressure area of the ball also increases.
When there is a shutoff differential pressure, the load acting on the ball may increase significantly.
If a floating ball structure is used, these loads are further transferred to the downstream seat, affecting seat load, friction, and operating torque.
A trunnion-mounted ball valve manages the ball load through its support structure, making it more suitable for large-diameter and relatively high-differential-pressure applications.
3. Can Floating Ball Valves Be Used in High-Pressure Pipelines?
Yes.
The pressure rating should not be determined simply by the fact that the valve uses a “floating ball” structure.
Some specially designed small-size floating ball valves can also be used at relatively high pressure ratings.
Whether a specific valve is suitable should be confirmed according to valve size, pressure rating, materials, seat design, sealing materials, and manufacturing standards, and the specific product data sheet should be used as the final reference.
4. Is the Operating Torque of a Trunnion-Mounted Ball Valve Always Lower Than That of a Floating Ball Valve?
Not necessarily.
Operating torque is also affected by many factors, including valve size, differential pressure, seat material, preload, sealing structure, temperature, and manufacturing design.
However, under the same or similar large-diameter and high-differential-pressure conditions, the trunnion-mounted structure supports the ball and is usually more favorable for managing the load and friction between the ball and seats, making operating torque easier to control.
5. How Can You Quickly Decide Between a Floating Ball Valve and a Trunnion-Mounted Ball Valve?
You can first focus on four core parameters:
Valve size, maximum shutoff differential pressure, seat load, and operating torque.
Generally speaking:
Small- and medium-sized valve + load and torque requirements are satisfied: a floating ball valve can be evaluated;
Large size + relatively high shutoff differential pressure + high requirements for torque control: a trunnion-mounted ball valve should be carefully evaluated.
However, this is not an absolute dividing line.
Final selection still needs to consider media, temperature, pressure rating, seat material, sealing requirements, actuation method, and relevant design standards.