Zhejiang Dongri Valve Co., Ltd.
Floating and trunnion-mounted ball Valves differ primarily in how the ball is supported and how sealing forces are managed. In a Floating Ball Valve, the ball is not fixed to a shaft and shifts slightly under fluid pressure, pressing against the downstream seat to create a reliable seal. This simple design is cost-effective and well suited to smaller Valve sizes and low-to-moderate pressure applications. A trunnion-mounted Ball Valve, by contrast, uses additional shafts to anchor the ball, reducing operating torque and minimizing pressure on the seats. As a result, it is better suited to large-diameter pipelines, high-pressure systems, frequent operation, and demanding industrial service. The right choice depends on valve size, pressure and temperature ratings, operating frequency, maintenance requirements, and budget. In short, floating valves offer simplicity and economy, while trunnion valves provide greater stability and performance in severe conditions.
Choosing between a floating ball valve and a trunnion ball valve can affect sealing, operating torque, maintenance, and project cost. The difference is not just the valve size. I need to look at pressure, temperature, media, operating frequency, pipeline design, and shutoff requirements before making a selection.
A valve that works well on a water line may not suit a high-pressure gas pipeline. Understanding how each ball valve supports its ball makes the choice easier.
A floating ball valve does not have a fixed lower stem or bottom support. The ball connects to the upper stem and can move slightly inside the valve body.
When line pressure pushes against the upstream side of the ball, the ball moves toward the downstream seat. This force helps the ball press against the seat and create a seal.
The design is simple:
This design is common in water treatment, compressed air, general industrial service, and many low- to medium-pressure applications.
A floating ball valve can offer reliable shutoff when the pressure, temperature, seat material, and media are within the valve’s rated range. It should not be selected by size alone.
A trunnion ball valve uses a fixed ball supported by a top stem and a lower trunnion. The ball rotates around a stable axis instead of moving toward the downstream seat.
The seats move toward the ball to maintain contact. Springs or line pressure may help push the seats against the ball, depending on the valve design.
Its main features include:
Trunnion ball valves are often found in pipeline stations, gas processing plants, oil transfer systems, power facilities, and other services where the valve may be large, pressurized, or operated through an actuator.
The exact performance depends on the design. A trunnion valve does not automatically provide every isolation feature. I need to confirm the product drawings, seat arrangement, cavity relief design, and test documents.
The clearest difference is the way the ball is supported.
A floating ball moves slightly under pressure. The pressure helps push the ball against the downstream seat. This can support a tight seal, but it also means the seat and ball can experience higher contact force as pressure rises.
A trunnion ball remains fixed in position. The seats move against the ball, while the support system carries the ball load. This arrangement can reduce the torque needed to turn the ball, especially on larger valves.
That difference affects the actuator, seat wear, valve size, and operating cost.
| Feature | Floating Ball Valve | Trunnion Ball Valve |
|---|---|---|
| Ball support | Supported mainly by the stem | Supported by a top stem and lower trunnion |
| Ball movement | Moves slightly under line pressure | Remains fixed while seats move |
| Operating torque | Can rise with valve size and pressure | Often lower for large or high-pressure valves |
| Internal design | Usually simpler | Usually has more parts |
| Purchase cost | Often lower | Often higher |
| Common use | Water, air, general process lines | Pipeline, gas, oil, high-pressure service |
| Maintenance | Fewer parts may simplify service | Seat and cavity design need closer review |
| Actuator demand | May be higher on larger sizes | Often more manageable on larger sizes |
| Double block and bleed | Depends on the design | Available on many pipeline models |
| Space and weight | Often compact | Can be heavier and more complex |
This table gives a useful starting point. It does not replace the valve data sheet or piping specification.
A floating ball valve may need more torque as pressure and size increase. The ball is pressed against the downstream seat, which increases friction during rotation.
A trunnion ball valve often needs less operating torque because the ball is supported by the trunnion. The seats are designed to maintain sealing contact without forcing the whole ball to move against a fixed seat.
This matters when I select a pneumatic, electric, or hydraulic actuator.
For a small valve on a utility water line, the torque difference may not affect the project much. For a large gas pipeline valve, actuator sizing can affect equipment cost, power demand, and installation space.
The actuator must be sized from actual valve torque data. I should not estimate it from nominal diameter alone.
Trunnion ball valves are often selected for large-bore and high-pressure applications because the fixed ball can reduce operating torque and mechanical load during operation.
Floating ball valves can also be designed for pressure service. Their use depends on:
A floating valve may be a practical choice for a moderate-pressure process line. A trunnion valve may offer better control of torque and actuator size on a high-pressure transmission line.
The pressure rating on the nameplate is only one part of the decision. Seat performance can change with temperature and media, so I always check the full operating range.
Both valve types can provide tight shutoff when correctly designed, manufactured, installed, and tested.
A floating ball valve uses upstream pressure to push the ball against the downstream seat. This design can work well for many isolation duties.
A trunnion ball valve uses seat movement, springs, line pressure, or a combination of these elements. Some models use a double-piston effect, where pressure can energize the seat in a specific direction.
The term “tight shutoff” needs a clear test standard. I may need to check API 6D, ISO 5208, API 598, or the project specification, depending on the service and valve type.
A valve with a suitable rating and test record is more useful than a general claim about sealing performance.
Floating ball valves have a simpler internal arrangement in many designs. This can make inspection and replacement more straightforward, especially on smaller process lines.
The seat may experience higher load because the ball moves toward it under pressure. Abrasive particles, poor flushing, and frequent operation can affect seat life.
Trunnion ball valves include more internal components, such as trunnions, bearings, springs, and seat systems. These parts can support stable operation, but they also require a clear maintenance plan.
For pipeline service, I pay attention to:
The maintenance method should match the manufacturer’s instructions. A valve should not be disassembled while it contains trapped pressure or hazardous media.
Imagine a municipal water plant with a DN100 line, moderate pressure, clean water, and manual operation. A floating ball valve may be a sensible option because the line does not need a large actuator or complex cavity control system.
Now consider a DN500 natural gas pipeline operating at high pressure with remote actuation. A trunnion ball valve may fit the service better because the fixed ball can help control operating torque, while the valve design may support pipeline isolation and actuator integration.
These examples are not fixed rules. A gas line may need special fire-safe and emissions requirements. A water line may contain suspended solids that affect seat selection. The media and operating conditions still control the decision.
I use this sequence when comparing the two designs:
Record the operating pressure and temperature.
Confirm the line size and valve pressure class.
Identify the media and any solids, particles, or chemicals.
Check whether the valve will work manually or with an actuator.
Estimate the operating frequency.
Review the required leakage rate and test standard.
Confirm whether double block and bleed is required.
Check cavity relief, drain, vent, and emergency shutdown needs.
Compare seat and body materials.
Review maintenance access, spare parts, and service support.
Compare the complete installed cost, not just the purchase price.
A low purchase price may not remain low if the actuator, maintenance access, or spare parts create extra project costs.
One common mistake is treating every large valve as a trunnion valve and every small valve as a floating valve. Size gives a useful clue, but it does not replace engineering review.
Another mistake is selecting a valve from pressure class alone. A valve may meet the pressure requirement while its seat material performs poorly with the actual chemical or temperature conditions.
Some buyers also focus only on body material. The stem seal, seat, ball coating, spring material, and fire-safe features may have a direct effect on service life.
A further concern is using a general valve for throttling service. Most ball valves are designed mainly for open or closed isolation. Repeated throttling can damage the seats and change flow behavior. A control valve may be more suitable when flow adjustment is a regular duty.
For a simple line with moderate pressure, limited operating frequency, and a need for a compact solution, a floating ball valve often deserves consideration.
For a large or high-pressure pipeline with actuator operation, frequent isolation, or strict isolation requirements, a trunnion ball valve may offer better control of torque and operating load.
Neither design is suitable for every project. I make the decision from the service data, not from the valve name or a general price comparison. When the pressure, temperature, media, actuator, and shutoff standard are clear, the difference between floating and trunnion ball valves becomes much easier to judge.
Choosing between a floating ball valve and a trunnion-mounted ball valve can affect operating torque, maintenance work, sealing performance, and project cost. The right option depends on line size, pressure, temperature, fluid type, valve operation, and shutdown requirements.
I often see buyers compare these valves by price alone. That approach can create problems later. A floating valve may suit a small water line, while a trunnion valve may be a better fit for a large gas pipeline. Both designs can perform well when the working conditions match their structure.
A floating ball valve has a ball that is not fixed to a lower support. The stem turns the ball, while the ball can move slightly inside the body.
When line pressure pushes the ball toward the downstream seat, the ball presses against the seat and helps create a seal. This simple design uses fewer internal parts and is common in many industrial systems.
A floating ball valve may fit your project when you need:
The valve is often easy to source and install. It is also widely used in water treatment equipment, small process skids, building services, and general industrial piping.
The main design limit appears as valve size and pressure increase. A larger ball may create more friction against the seats. The actuator may need more torque, and seat wear can become a concern if the valve cycles often or handles abrasive media.
A trunnion ball valve uses a fixed support system. The ball is held by a stem at the top and a trunnion at the bottom. The ball rotates in place instead of moving toward the downstream seat in the same way as a floating ball.
The seats move toward the ball under the action of springs or line pressure. Since the ball carries less side load, the valve can require lower operating torque, especially in larger sizes and higher-pressure services.
A trunnion ball valve may fit your project when you need:
Many trunnion valves include a body cavity relief design. This feature can help manage pressure trapped inside the valve body, but its exact function depends on the valve design and project specification.
Trunnion valves usually have a higher purchase price. Their internal structure is also more complex, so inspection and repair may require trained technicians and suitable spare parts.
The biggest strength of a floating ball valve is its simple construction. Fewer supporting parts can make the valve easier to handle and more affordable for many applications.
A typical example is a water treatment skid with a 2-inch or 3-inch process line. The pressure is within the valve rating, the operating frequency is moderate, and the fluid is clean. A floating ball valve may provide suitable shutoff without adding unnecessary cost or weight.
There are limits to consider:
A floating design should not be selected only because the valve looks compact. The seat material, pressure rating, temperature range, and fluid condition still need to match the system.
A trunnion ball valve distributes mechanical loads through its support structure. This can reduce the force needed to rotate the ball and support stable operation in larger systems.
For example, a natural gas pipeline may use a large-diameter valve that opens during line operation and closes during maintenance isolation. In this setting, actuator torque, pressure rating, sealing design, and emergency shutdown requirements all matter. A trunnion ball valve may offer a more suitable arrangement than a floating design.
Its limits include:
The valve is not automatically the right choice for every high-pressure application. The manufacturer’s pressure-temperature chart, test standard, fire-safe design, and sealing arrangement should be reviewed before approval.
| Feature | Floating Ball Valve | Trunnion Ball Valve |
|---|---|---|
| Ball support | Ball moves slightly under pressure | Ball is supported by a trunnion and stem |
| Typical use | Small to medium lines | Medium to large lines |
| Operating torque | Can increase with size and pressure | Often lower for larger valves |
| Construction | Simpler | More complex |
| Purchase cost | Often lower | Often higher |
| Maintenance | Usually straightforward | May require more technical work |
| Frequent cycling | Depends on seat and service conditions | Often suitable when properly specified |
| Pipeline isolation | Used in selected duties | Common in larger pipeline systems |
These points describe common design behavior. Actual performance depends on valve size, pressure class, seat material, fluid, temperature, actuator, and operating cycle.
I use a practical review process before making a recommendation.
Small process lines often work well with floating ball valves. As the bore becomes larger, the ball weight, seat load, and actuator torque become more relevant.
Large pipeline valves often need the support provided by a trunnion design.
Review the maximum working pressure, minimum and maximum temperature, and pressure changes during startup and shutdown.
Do not rely on the nominal pipe size alone. A valve used with hot oil, high-pressure gas, steam-related service, or cryogenic fluid may need a special body and seat arrangement.
Clean water and air are usually easier on sealing surfaces than fluids containing sand, solid particles, or chemical components.
For natural gas, petroleum products, and process chemicals, I check body materials, seat materials, stem seals, emission requirements, and compatibility data.
A valve that opens twice a year has a different duty from a valve that cycles every hour.
Frequent operation can increase seat and stem wear. The valve supplier should receive the expected cycle count and operating speed so the design can be reviewed properly.
The actuator must provide enough torque throughout the operating cycle. The required torque may change with pressure, temperature, seat material, and service condition.
A floating valve in a larger size may need a larger actuator than expected. A trunnion valve may reduce the torque requirement, but the final actuator selection still needs manufacturer data.
Ask how the valve will be isolated, tested, drained, and repaired.
For pipeline systems, features such as double block and bleed, cavity relief, body venting, drain connections, and emergency shutdown compatibility may affect the choice. These features are not identical on every model.
The purchase price is only one part of the decision. I also review:
A lower-cost valve may become less suitable if it requires frequent seat replacement or a larger actuator.
One common mistake is using a floating valve on a large, high-pressure line without checking torque and seat loading.
Another mistake is choosing a trunnion valve for a small utility line when a simpler floating design would meet the operating needs. The extra structure may add cost and weight without providing a clear benefit.
I also recommend checking the actual valve data sheet instead of relying on a general product label. “High pressure” can mean different things across manufacturers and standards. The pressure class, body material, seat rating, test pressure, and temperature limits should appear in the technical documents.
Installation can affect service life as well. Pipe stress, poor alignment, contaminated fluid, incorrect actuator settings, and unsuitable welding procedures may damage a valve that was correctly selected on paper.
Imagine two projects.
The first project uses a 2-inch water line in a commercial treatment room. The valve operates several times each week, pressure remains within the standard rating, and the fluid contains limited solid matter. A floating ball valve may provide a practical balance of cost, size, and maintenance access.
The second project uses a 24-inch natural gas pipeline. The valve must isolate a long section of pipe, operate with an actuator, and handle a higher pressure class. Torque, sealing reliability, cavity pressure control, and shutdown testing become more important. A trunnion ball valve may be a more suitable direction, subject to the project specification and supplier review.
The difference comes from the service conditions, not from one design being suitable for every system.
Choose a floating ball valve when the line is smaller, the pressure is moderate, the fluid is suitable, and the operating cycle does not place excessive demand on the seats.
Consider a trunnion ball valve when the line is large, the pressure is high, the valve cycles often, or the system requires pipeline isolation features and controlled actuator torque.
Before placing an order, prepare the line size, pressure, temperature, fluid details, valve rating, connection standard, operating frequency, actuator requirements, and inspection needs. Share these details with the supplier and ask for the torque data, pressure-temperature limits, material list, test documents, and maintenance instructions.
A good valve choice starts with the service conditions. The name of the design matters less than how well its structure matches the work it must perform.
Choosing a ball valve can look simple until the line carries high pressure, large flow, corrosive media, or frequent cycling. A floating ball valve and a trunnion-mounted ball valve may share the same basic design, yet they manage pressure and operating torque in different ways.
I focus on three questions when comparing them:
The right choice depends on pressure, size, media, operation frequency, and maintenance needs.
In a floating ball valve, the ball is not fixed to a lower stem or support shaft. The stem turns the ball, while the ball can move slightly inside the body.
When line pressure pushes against the upstream side of the ball, the ball moves toward the downstream seat. This contact helps create a tight seal.
The design is relatively simple:
I often see floating ball valves used in water systems, air lines, low-pressure gas service, chemical lines, and general process equipment. They suit many small and medium-size pipelines where the pressure load stays within the valve’s design range.
A floating ball valve can offer several practical advantages:
The lighter structure can help when space around the pipeline is limited. A manually operated floating valve may also be easier to install in smaller lines.
The ball presses against the downstream seat as line pressure increases. That contact creates the seal, yet it also creates friction.
This can lead to:
A floating ball valve may not be the right fit for a large, high-pressure pipeline that opens and closes many times each day. The design can still work in demanding service, but the seat material, pressure class, actuator size, and operating cycle all need careful review.
A trunnion ball valve uses a fixed ball. The ball is supported by a stem at the top and a trunnion, or support shaft, at the bottom.
The ball rotates around a fixed center. Line pressure does not push the entire ball toward the downstream seat in the same way as a floating design.
Spring-loaded seat rings move toward the ball to maintain contact. This arrangement reduces the force needed to rotate the ball, especially in larger sizes and higher-pressure applications.
A trunnion-mounted design often appears in:
The fixed-ball structure can provide useful operating advantages:
For example, a pipeline operator may need a 20-inch valve connected to a pneumatic actuator. A floating design could require a large actuator because the ball must push against the seat while turning. A trunnion design can reduce this load by supporting the ball inside the body.
A trunnion ball valve usually has more internal parts and a more complex structure. This can affect cost, weight, and service work.
Possible drawbacks include:
The fixed-ball design does not make the valve suitable for every application. Seat material, cavity pressure, fire-safe design, stem sealing, and media compatibility still require review.
| Feature | Floating Ball Valve | Trunnion Ball Valve |
|---|---|---|
| Ball support | Ball moves slightly | Ball is fixed by support shafts |
| Sealing force | Line pressure pushes ball into seat | Spring-loaded seats press toward ball |
| Operating torque | Usually higher as size and pressure rise | Usually lower for large, high-pressure valves |
| Body design | Simpler | More parts and support components |
| Common size range | Small to medium pipelines | Medium to large pipelines |
| Cost | Often lower | Often higher |
| Actuator demand | Can be higher | Often lower for similar service |
| Maintenance | Simple for many models | Requires more detailed procedures |
| Typical use | General process, water, air, moderate pressure | Pipeline, high pressure, large bore service |
This table gives a useful starting point, yet valve selection should not rely on size alone. A small valve handling high-cycle abrasive media may need more careful review than a large valve used only a few times each year.
I start with nominal pipe size, pressure rating, and temperature. A floating design may suit a smaller line with moderate pressure. A trunnion design becomes more attractive as bore size and pressure increase.
The valve must match the actual system conditions, not only the normal operating point. Startup pressure, pressure surges, shut-in pressure, and low-temperature conditions can change the load on the valve.
A valve that stays open for months has different needs from a valve that cycles every hour.
Frequent cycling increases the effect of:
A trunnion valve may help reduce torque in a high-cycle system, while a floating valve may remain a practical choice for occasional isolation.
Clean water, dry gas, steam, slurry, crude oil, and chemical fluids place different demands on seats and seals.
I check:
Soft seats can provide tight shutoff, but they may not suit high temperatures or abrasive particles. Metal-seated versions can handle harsher service, though they require suitable design, surface treatment, and testing.
The actuator must provide enough torque throughout the full operating stroke. The required value can change with pressure, temperature, seat material, media, and valve condition.
Using only the valve’s nominal size to select an actuator can create problems. An undersized actuator may fail to close the valve. An oversized actuator can place extra load on the stem, gearbox, or valve body.
I prefer to request a torque chart from the valve manufacturer and include a suitable safety margin based on the service conditions.
A simple valve may be easier to service, but access around the installed valve also matters.
Before placing an order, I review:
A valve that is easy to repair in a workshop may be difficult to service when installed high above the floor or inside a crowded skid.
Imagine a clean-water line with a moderate pressure rating, a small bore, and manual operation. The valve opens only during planned maintenance. A floating ball valve may provide suitable shutoff with a simple layout and manageable cost.
Now consider a high-pressure gas pipeline with a large bore and pneumatic operation. The valve may need to close during an emergency and remain reliable after long periods without movement. A trunnion-mounted ball valve may be a better match because its support structure can reduce operating torque and actuator demand.
These examples are starting points, not automatic rules. The final choice still depends on the manufacturer’s design data, applicable standards, test requirements, and site conditions.
I see several repeated mistakes during valve selection.
A lower purchase price may not reflect actuator cost, maintenance access, replacement seats, or downtime. The full service requirement gives a better basis for comparison.
A valve may work at normal pressure but face a different load during startup, shutdown, or line packing. These conditions should be included in the review.
A valve used for clean water may not suit slurry, high-temperature oil, or corrosive chemicals. Seat and seal materials need to match the medium.
Torque can change with pressure, temperature, seat wear, and long idle periods. The actuator selection should use the manufacturer’s complete torque data.
Some ball valves can trap pressure inside the body cavity. In certain systems, a self-relieving seat or an external relief arrangement may be needed. The selection should follow the process design and safety requirements.
A floating ball valve may fit when the system needs:
A trunnion-mounted ball valve may fit when the system needs:
My main advice is to compare the complete valve package rather than the body design alone. Review the pressure, temperature, media, cycle rate, torque, actuator, seat material, testing, and maintenance plan together. A floating valve and a trunnion valve can both perform well when the design matches the service. The problem starts when the valve is selected from size or price without checking how the pipeline will actually operate.
Selecting a ball valve is not only a matter of checking the pipe size and pressure rating. The internal support design also affects operating torque, sealing behavior, maintenance work, and the space needed around the valve.
The two common choices are floating ball valves and trunnion-mounted ball valves. Each design can work well when it matches the service conditions. A mismatch may lead to high operating torque, seat wear, leakage, or difficult maintenance.
I usually start with one question: what will the valve face during service?
How a floating ball valve works
A floating ball valve has a ball that is not fixed to a lower stem or support. The ball moves slightly under line pressure. This movement pushes the ball against the downstream seat and helps form the seal.
The design has a simple internal structure. It is often used for small and medium pipe sizes, moderate pressure duties, water systems, air lines, gas service, and general process applications.
A floating ball valve may be a practical choice when:
The ball is held in place by the seats and the stem. As pressure rises, the force acting on the ball also rises. That force can increase seat friction and operating torque.
This point matters when the valve is connected to a pneumatic or electric actuator. A hand lever may operate a small valve without difficulty, while the same design in a larger size may need more force than the actuator can provide.
How a trunnion-mounted ball valve works
A trunnion ball valve uses a fixed ball supported by a lower shaft, called a trunnion, and an upper stem. The ball rotates around a stable axis instead of moving freely toward the downstream seat.
The seat rings move toward the ball to maintain contact. Since the line pressure does not push the full ball into the seat, the operating torque can be lower than that of a floating design at similar pressure and size.
Trunnion-mounted valves are often considered for:
This design has more internal parts and may cost more. It also needs careful attention to seat design, sealing materials, cavity pressure, drain points, and maintenance access.
A trunnion valve is not automatically the right choice for every large valve. The actual selection still depends on pressure, temperature, medium, cycle frequency, emissions requirements, and the manufacturer’s design data.
Floating or trunnion: a practical comparison
A floating ball valve is usually simpler and more compact. Its internal structure can make inspection and replacement work easier in some applications. The purchase price may also be lower, though the final cost depends on materials, pressure class, testing, and actuator requirements.
A trunnion ball valve provides a fixed ball support. This can reduce operating torque and make it more suitable for large, high-pressure, or frequently operated valves. The body and support arrangement add design complexity, so the valve may require a higher initial budget and more detailed maintenance planning.
The choice becomes clearer when I compare the main factors.
Pipe size
Small and medium lines often use floating ball valves. Large lines may use trunnion-mounted valves because the weight of the ball and the operating force can become difficult to manage with a floating design.
Pipe size alone should not decide the selection. A small valve in high-cycle service may still need a trunnion design, while a large valve in low-pressure water service may use a floating design if the supplier confirms the torque and seat performance.
Pressure and temperature
Pressure changes the load on the ball, seats, stem, and body. Higher pressure can increase the force required to turn a floating ball valve. Temperature also affects seat materials, body expansion, lubricant behavior, and sealing performance.
I check the valve pressure-temperature table rather than relying only on the nominal pressure class. The body rating and the seat rating may not be identical across all temperature ranges.
A valve used for hot oil, steam-related service, or low-temperature gas needs materials selected for that temperature. PTFE, reinforced PTFE, PEEK, nylon, metal seats, and other materials have different service limits. The supplier should provide the recommended range for the actual medium.
Operating frequency
A valve that moves once during commissioning has different needs from a valve that cycles several times each day.
Frequent cycling can increase wear at the seats, stem seals, bearings, and actuator connection. A trunnion-mounted design may reduce the torque demand, but the seats still need to match the medium and cycle conditions.
I ask for the expected number of cycles across the valve’s service period. “Open and close occasionally” is not enough information for a proper actuator and seat selection.
Medium and contamination
Clean water, dry gas, chemicals, slurry, and abrasive fluids place different demands on a ball valve.
Solid particles can damage sealing surfaces or become trapped near the seats. A floating ball valve may be suitable for some clean services, while a trunnion valve with a suitable seat and cavity design may be selected for larger process lines. Neither design should be chosen for abrasive service without checking the manufacturer’s test data and material recommendations.
The medium also affects corrosion resistance. Body, ball, stem, seat, and seal materials should be reviewed as a complete set. Choosing a corrosion-resistant ball while overlooking the stem or bolting can create a weak point in the system.
Actuator and torque
The actuator must deliver enough torque throughout the valve’s operating cycle. Breakaway torque, running torque, and seating torque can differ.
I do not select an actuator from the valve size alone. I request the valve torque data at the lowest and highest expected pressure, then allow for the supplier’s stated safety margin. The actuator output should also be checked against the valve’s maximum allowable stem torque.
A floating valve may need a larger actuator as pressure rises. A trunnion valve may reduce the torque requirement, yet its actuator still needs to handle seat friction, packing load, low-temperature effects, and any pressure difference across the ball.
Real service examples
A water treatment plant may use floating ball valves on smaller utility lines. The pressure is moderate, the medium is relatively clean, and the valves do not cycle continuously. A compact design can make sense when the body material and seals match the water quality.
A gas transmission station may use trunnion-mounted ball valves on large isolation lines. These valves may stay open for long periods and close during maintenance or an emergency shutdown sequence. The project team may focus on actuator torque, low-emission stem sealing, fire-safe design, cavity pressure management, and pipeline cleaning requirements.
A chemical plant may need a different approach. The line size could be modest, but the fluid may be corrosive or operate at an elevated temperature. In that case, seat and seal compatibility can matter more than the floating or trunnion label. A smaller floating valve with suitable materials may perform better than a larger valve with unsuitable seats.
A selection process I use
I gather the operating data before contacting suppliers:
I then compare the valve design with the actual duty.
For a floating valve, I check ball loading, seat friction, stem torque, and actuator capacity. For a trunnion valve, I review the support system, seat movement, cavity relief, drain and vent options, and maintenance method.
I also confirm the applicable product and project standards. API 6D may apply to pipeline valves, while ASME B16.34 covers pressure-temperature ratings, materials, and testing requirements for many industrial valves. The project specification may require additional tests, such as fire-safe, fugitive-emission, low-temperature, or gas-tightness testing.
The manufacturer’s data sheet should state the body material, ball and stem material, seat material, pressure rating, temperature range, end connection, test standard, and actuator interface. Those details help prevent a low-cost selection from creating higher costs during installation or operation.
Common selection mistakes
One common mistake is choosing a floating ball valve because the line is small, without checking the cycle frequency and pressure difference.
Another mistake is choosing a trunnion valve only because the pressure rating looks high. A more complex valve does not correct a material mismatch, an unsuitable seat, or poor actuator sizing.
Some buyers compare only the purchase price. The valve may require an actuator, gearbox, mounting kit, spare seats, special testing, and a different maintenance plan. These items can change the total project cost.
I also avoid treating “full bore” as a complete performance description. Bore size affects pressure loss and pipeline pigging, but it does not describe sealing materials, torque, emissions, or service life.
The right ball valve is the one that matches the pressure, temperature, medium, pipe size, operating pattern, and maintenance plan. Floating valves suit many general and moderate-duty applications. Trunnion-mounted valves often fit larger, higher-pressure, or frequently actuated systems.
I recommend starting with operating data rather than a preferred valve type. When the service conditions are clear, the choice becomes easier to explain, compare, and verify with the supplier.
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American Petroleum Institute 2021 Pipeline and Piping Valves API Specification 6D
International Organization for Standardization 2015 Industrial Valves Pressure Testing of Metallic Valves ISO 5208
American Society of Mechanical Engineers 2022 Valves Flanged Threaded and Welding End ASME B16.34
International Organization for Standardization 2023 Petroleum and Natural Gas Industries Pipeline Transportation Systems Pipeline Valves ISO 14313
American Petroleum Institute 2022 Fire Test for Quarter-Turn Valves and Valves with Nonmetallic Seats API Standard 607
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