1. What Is a Fixed Ball Valve?

A fixed ball valve (also commonly called a trunnion Mounted Ball valve) is a ball valve

in which the ball is supported by trunnions at the top and bottom. The ball is held firmly in position and does

not move downstream under pressure. Instead, the seats are spring‑loaded or pressure‑energized and move toward

the fixed ball to achieve tight shut‑off.

In fixed ball valves, the stem is connected to the top of the ball, and the bottom of the ball is guided by a

trunnion or bearing. This design is widely used in high‑pressure, large‑diameter and severe service applications,

such as transmission pipelines and critical block valves in the oil and gas industry.

1.1 Key Characteristics of Fixed Ball Valves

• Ball supported at both top (stem) and bottom (trunnion or shaft).
• Seats are movable and pressed against the ball by springs and/or line pressure.
• Torque is generally lower than comparable Floating ball valves at high pressure.
• Suitable for large nominal sizes (e.g. up to DN 1400 / 56″ or larger) and high pressure ratings (e.g. Class 150–2500).
• Often available in side‑entry, top‑entry and fully welded body configurations.

1.2 Basic Structure of a Fixed Ball Valve

Although many design variations exist, a typical fixed ball valve includes the following components:

• Body (one‑piece, two‑piece or three‑piece casting or forging).
• Trunnion mounted ball with precision machined bore.
• Upper stem and lower trunnion.
• Self‑energized or spring‑loaded seats.
• Stem sealing system (gland packing, O‑rings, fire‑safe seals).
• Seat sealing system (soft seat, metal‑to‑metal, or composite design).
• Antistatic devices, stem blow‑out proof design, vent and drain ports (depending on standard).

2. What Is a Top Entry Ball Valve?

A top entry ball valve is a ball valve in which the internal trim (ball, seat rings, stem and related

components) can be accessed and removed from the top of the valve body without removing the valve from the

pipeline. Typically, the valve has a body with an integral bottom part and a removable top cover or bonnet.

Top entry ball valves are often, but not always, trunnion mounted. Many top entry ball valves are fixed ball

valves by construction, combining the benefits of trunnion support with top entry maintenance capability. This

makes the top entry design popular in buried or hard‑to‑access pipelines, subsea systems and applications with

strict shutdown and maintenance constraints.

2.1 Key Characteristics of Top Entry Ball Valves

• One‑piece body with a removable top cover or bonnet.
• Internal parts can be serviced, inspected or replaced from the top.
• Often used in pipelines where online maintenance is required.
• Lower number of body joints and potential leakage paths compared to side‑entry multi‑piece designs.
• Commonly used in high‑pressure, high‑temperature and safety‑critical applications.

2.2 Basic Structure of a Top Entry Ball Valve

A typical top entry ball valve includes:

• One‑piece body with integral flow passage.
• Top bonnet or cover bolted to the body.
• Ball (often trunnion mounted), seats and seat carriers.
• Stem, stem bearings and packing system accessible from the top.
• Gaskets and sealing surfaces between body and bonnet.
• Actuator mounting flange and drive arrangement.

3. Design and Construction Comparison

The concepts of a fixed ball valve and a top entry ball valve refer to different

aspects of design:

• “Fixed ball” describes how the ball is supported and loaded (trunnion mounting).
• “Top entry” describes how the valve internals are accessed (maintenance and body design).

As a result, some valves are both fixed ball and top entry. However, for comparison purposes, many engineers

contrast a fixed ball side‑entry valve with a fixed ball top entry valve because these represent two

common design philosophies in pipeline construction.

3.1 Structural Comparison Table

3.2 Body Types and End Connections

Both fixed ball valves and top entry ball valves can be supplied with various body configurations and end

connections:

• Body configurations:

  • One‑piece (integral body).
  • Two‑piece (split body).
  • Three‑piece (central body plus two end caps).
  • Fully welded body (commonly used in buried gas pipelines).

• End connections:

  • Flanged according to ASME, EN or other standards.
  • Butt weld ends for high‑pressure pipelines.
  • Socket weld or threaded ends for smaller sizes.

4. Working Principle and Sealing Performance

4.1 Working Principle of Fixed Ball Valves

The working principle of a fixed ball valve is based on a trunnion supported ball that rotates 90° between open

and closed positions. The ball is fixed axially, while the seats move under spring force and line pressure to

press against the ball surface.

• In the open position, the ball bore aligns with the pipeline, allowing full‑bore or reduced‑bore flow.
• When the valve closes, the actuator rotates the stem, turning the ball so its solid side faces the seats.
• Springs behind the seats and fluid pressure drive the seats toward the fixed ball, creating tight sealing.
• Fixed ball design minimizes side loading on the stem, reducing operating torque and wear.

4.2 Working Principle of Top Entry Ball Valves

Top entry ball valves operate in the same basic way as other ball valves (quarter‑turn shut‑off), but the body

and bonnet arrangement allows access from the top:

• The ball and seats (often trunnion mounted) rotate and seal similarly to fixed ball designs.
• The difference is that the valve internals are assembled into the body from the top opening.
• During maintenance, the bonnet is removed to extract the ball, seats and stem without cutting the valve out of the line.
• Bonnet gaskets and body‑bonnet sealing surfaces are critical for overall sealing performance.

4.3 Sealing Performance Comparison

5. Advantages and Disadvantages

5.1 Advantages of Fixed Ball Valves

• Low operating torque at high pressure due to balanced force distribution on the trunnion supported ball.
• Reliable sealing under high differential pressure, including double block and bleed (DBB) or double isolation configurations.
• Suitable for large diameters, offering stable operation and less stem and seat wear.
• Versatile design options such as side entry, top entry, fully welded and cryogenic versions.
• Wide range of materials and trims to match corrosive, erosive and high‑temperature media.

5.2 Disadvantages of Fixed Ball Valves

• More complex internal structure than floating ball valves, leading to higher manufacturing cost.
• In some side‑entry designs, difficult inline maintenance; valve may need to be removed from pipeline.
• Larger footprint and weight in big sizes compared to simpler valves like gate valves.

5.3 Advantages of Top Entry Ball Valves

• Inline maintenance: ball, seats and stem can be serviced from the top without removing the valve from the pipe.
• Reduced leakage paths: one‑piece body with a single bonnet joint minimizes external leak points.
• Ideal for buried or welded pipelines, where cutting the valve out is expensive and time‑consuming.
• Good for high integrity and critical services, including high pressure, high temperature and emergency shutdown positions.
• Simplified pipeline layout: no need for large lateral space to disassemble side‑entry body.

5.4 Disadvantages of Top Entry Ball Valves

• Higher initial cost due to complex body machining and bonnet sealing design.
• More stringent manufacturing tolerances needed to ensure proper alignment of ball and seats from top assembly.
• Maintenance space required above the valve for bonnet removal and lifting of internal components.
• For very large diameters, the bonnet and internal weights can require heavy lifting equipment.

5.5 Summary Comparison Table: Pros and Cons

6. Typical Applications

6.1 Applications of Fixed Ball Valves

• Oil and gas transmission pipelines (onshore and offshore).
• Block and bleed stations, block valves, pig launcher and receiver stations.
• Refinery and petrochemical process units requiring high‑pressure isolation.
• Natural gas distribution networks and compressor station manifolds.
• Power generation plants, including steam and cooling water systems (with appropriate materials).
• High‑pressure water injection and produced water handling systems.

6.2 Applications of Top Entry Ball Valves

• Buried pipelines where removing the valve is difficult and costly.
• Offshore platforms and FPSO installations requiring compact and maintainable valves.
• Subsea production systems (specifically engineered subsea top entry variants).
• Facilities with strict downtime limitations and high maintenance frequency.
• High‑integrity pressure protection systems (HIPPS) and emergency shutdown valve (ESDV) applications.
• Critical process units in refineries, chemical plants and LNG facilities.

6.3 Industry Comparison Table

7. Material and Specification Overview

Both fixed ball valves and top entry ball valves can be manufactured in a wide range of materials for different

fluids, temperatures and corrosive conditions. The specification range is similar for the two types, although

top entry valves are more frequently selected for severe or safety‑critical services where maintenance is a key

concern.

7.1 Common Body Materials

• Carbon steel (e.g. ASTM A105, A216 WCB, A350 LF2).
• Low‑temperature carbon steel (e.g. A352 LCB, LCC).
• Stainless steel (e.g. ASTM A182 F304, F304L, F316, F316L).
• Duplex and super duplex stainless steels for high chloride environments.
• Alloy steels for high‑temperature service.
• Nickel‑based alloys for highly corrosive or sour service.

7.2 Seat and Seal Materials

• Soft seats: PTFE, reinforced PTFE, PEEK, nylon and other engineering plastics.
• Metal‑to‑metal seats: hard‑faced with tungsten carbide, chromium carbide or other wear resistant alloys.
• Elastomeric O‑rings and gaskets: Viton, NBR, HNBR, FFKM depending on fluid compatibility.
• Graphite packing and gaskets for fire‑safe and high‑temperature service.

7.3 Typical Pressure and Temperature Ratings

The following table provides a general view of specification ranges; actual values depend on design and material:

8. Selection Guide: How to Choose Between Fixed Ball and Top Entry Ball Valves

Selecting between a fixed ball valve and a top entry ball valve is not always a direct

one‑to‑one choice because many top entry valves are themselves fixed ball designs. However, in practice, project

teams often compare:

• Fixed ball side‑entry valves vs fixed ball top entry valves.
• Fixed ball valves vs other valve types where top entry is an option.

8.1 Key Selection Factors

• Accessibility and Maintenance Strategy:

  • If the valve is buried, subsea or difficult to remove, a top entry ball valve offering inline maintenance is typically preferred.
  • If valves are installed above ground with good access and spare valves are available, side‑entry fixed ball valves may be more cost‑effective.

• System Criticality and Downtime Costs:

  • For critical isolation in high value streams where downtime is very expensive, top entry ball valves can reduce maintenance time.
  • For less critical services, fixed ball valves with conventional side‑entry design may be sufficient.

• Pipeline Design and Space Constraints:

  • Top entry ball valves require vertical clearance above the valve for bonnet removal.
  • Side‑entry fixed ball valves may require lateral space for body extraction or pipeline separation.

• Pressure, Temperature and Size:

  • Both valve types handle high pressure and large diameters, but verify standards and qualification for each project.
  • Cryogenic top entry ball valves are often used when inline access to cold box or LNG lines is required.

• Budget and Lifecycle Cost:

  • Initial cost of top entry ball valves tends to be higher.
  • Lifecycle cost may be lower if frequent maintenance or inspection is expected.

8.2 Practical Decision Matrix

9. Installation and Maintenance Considerations

9.1 Installation of Fixed Ball Valves

• Ensure correct orientation if the valve is designed for unidirectional flow or specific upstream/downstream seat functionality.
• Support the valve properly during installation to avoid excessive stress on pipeline flanges and welds.
• When fully welded bodies are used, perform required non‑destructive testing (NDT) on welds and verify coating or wrapping for corrosion protection.
• Check actuator alignment and torque settings before commissioning.

9.2 Installation of Top Entry Ball Valves

• Provide adequate vertical clearance above the valve for bonnet removal and lifting equipment.
• Ensure body‑to‑bonnet bolting is tightened according to specified torque values and patterns.
• Verify accessibility of stem, gland and any emergency sealant injection fittings from operating platforms.
• Pay special attention to gasket selection between body and bonnet to match pressure and temperature rating.

9.3 Maintenance of Fixed Ball Valves

• Side‑entry valves may require pipeline isolation, depressurization and removal for major overhauls.
• Routine checks include stem packing adjustment, actuator calibration and leakage testing.
• In systems with dirty or particulate media, consider periodic flushing to reduce seat wear.

9.4 Maintenance of Top Entry Ball Valves

• Isolate and depressurize the valve, then remove bonnet bolts to access the internals.
• Ball and seats can be inspected, lapped or replaced without removing valve body from pipeline.
• After maintenance, ensure correct reassembly of seat springs, seals and gasket; perform pressure test according to standards.
• Document torque and alignment settings to maintain consistent performance over the valve’s lifecycle.

10. Relevant Standards and Certifications

Fixed ball valves and top entry ball valves used in industrial pipelines are usually designed, manufactured and

tested according to recognized international standards. Typical references include:

• API 6D – Specification for Pipeline Valves.
• API 608 – Metal Ball Valves – Flanged, Threaded and Welding Ends.
• ASME B16.34 – Valves – Flanged, Threaded and Welding End.
• ISO 14313 – Petroleum and natural gas industries – Pipeline transportation systems – Pipeline valves.
• EN 1983 / EN 12516 – Industrial valves standards (Europe).
• Fire‑safe standards such as API 607 or ISO 10497 for fire‑tested designs.
• Fugitive emission standards such as ISO 15848 or API 641 for low emission designs.
• Compliance with PED, ATEX or local regulations depending on installation region.

When comparing fixed ball valves vs top entry ball valves, verify that each candidate design meets the project’s

applicable standards, certification requirements and project specification documents.

11. Summary of Fixed Ball Valve vs Top Entry Ball Valve

Fixed ball valves and top entry ball valves are not mutually exclusive categories. Many top entry valves use a

trunnion mounted fixed ball as the closure element. However, from a practical engineering and procurement

perspective, the comparison between a fixed ball valve and a top entry ball valve focuses on

differences in body design, maintenance philosophy, cost profile and leakage control.

• Fixed ball valves (trunnion mounted) are ideal for high‑pressure, large‑diameter applications,

  offering low operating torque, reliable sealing and flexible body configurations. Side‑entry versions are

  widely used where standard removal and maintenance practices are acceptable.

• Top entry ball valves are optimized for inline maintenance through a removable bonnet, reducing

  external leakage paths and minimizing downtime, especially in buried, offshore or highly critical services.

When choosing between the two, consider accessibility, pipeline configuration, maintenance strategy, pressure and

temperature conditions, as well as the balance between initial investment and lifecycle cost. A well‑structured

fixed ball valve vs top entry ball valve comparison within project design documents helps ensure safe,

economical and reliable pipeline operation over the entire service life of the facility.