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What is a trunnion ball valve?

Trunnion Ball Valve

What is a Trunnion Ball Valve

The trunnion ball valve is a vital device for regulating the flow of fluids, such as steam, gas, or oil, in a pipeline. It’s a quarter-turn design with a ball that can rotate 90 degrees on its axis to limit or allow fluid movement. The core of these valves has a spherical disk design that revolves to regulate the start-stop flow cycle. The disk, also known as the ball, has a little projecting shaft at the top and bottom that is mechanically supported. The position of a hole in the center of the ball controls flow in this example. Because of their versatility, trunnion-mounted ball valves are useful in enterprises that require such shut-off action.

Trunnion ball valves have sufficient support for the ball. The support is shaped like a shaft and is known as a trunnion. The Trunnion soaks up any additional pressure from the flow, lowering the pressure on the valve seat and the ball. Trunnion-mounted ball valves are used in large-scale implementations that require low operating torque.

How Does a Trunnion Ball Valve Work

A trunnion valve is a device that controls the flow of fluids in pipelines by regulating the shut-off cycle. It contains the elements required to enable or disable fluid flow through the pipe. It is designed to integrate pipe or tube pieces to perform this function.

What Is the Trunnion Ball Valve Structure?

Trunnion ball valves have a similar structure to traditional ones. The ball valves differ in that they have more mechanical anchors to sustain the ball. The ball is solidly supported on its x-axis by the two ends. It secures it and makes it very easy to control.

The design of the trunnion-mounted ball valve has dismal tended shafts at the top and bottom that are mechanically supported. This makes it suited for greater diameters and higher pressures. Squeezing the seat rings at the two ends keeps the ball in place in the trunnion-mounted system.


Because of its elasticity, the ball allows for a good amount of movement. When in use, it floats downstream towards the seat ring to form a seal. If the weights on the floating ball get significantly higher, the seat rings will be unable to sustain the ball. This is where the trunnion’s power comes into play. In a trunnion design, the sections that float are the seat rings, as opposed to the typical version, in which the ball floats.


The body is the housing that holds it in place and provides support for the inside of the ball valve. Depending on the use, the material for this design can be constructed of a variety of materials. Some commonly used materials are carbon steel, low-temperature carbon steel, stainless steel, duplex, Inconel, and super duplex.


This is a sphere ball-shaped disk that rotates in a solid rotating motion to halt or start flow. It is joined at one end to the Trunnion and at the other to the stem. While rotating, the ball is secured in place. The seat of a trunnion ball valve is in constant contact with this ball, which reduces torque.


Trunnion ball valves have a seat that is a design feature that surrounds the sphere.When the actuator gets turned on, the seats keep the ball tightly in place, blocking access. There are two types, i.e., metal and soft (Teflon). It will now move in the direction of the ball.


An extra shaft in the trunnion ball valve grips the ball in position from beneath. This simple shaft is the Trunnion, and Its function is to keep the ball firmly attached. The Trunnion is an extension of the spherical ball in some trunnion-mounted ball valves, while in others, it is joined to the spherical ball disk by welded connections.


The trunnion ball valve stem connects the ball to the actuator. It is connected to the ball by an additional shaft that helps secure the ball in place. Also, it regulates the ball’s movement. Trunnion-mounted ball valves have strengthened anti-blowout stems, which is why they can handle pressurized and intense temperatures without causing any damage.


Injection fittings are built into the seat and stem. When sealing is weakened, and leakage occurs, the grease can be injected through a sealant injection fitting; the injected sealant acts as a partial seal to prevent additional leaking.

Trunnion Ball Valve Design Standard

API6D or API608 design the trunnion ball valve, which meets industry requirements such as ASME B16.5, ASME B16.34, and ASME B16.10. They are designed to be fire resistant in accordance with API 607.

What Are the Primary Characteristics of a Trunnion Ball Valve?

Emergency Seal

A trunnion-mounted ball valve is designed to have a sealant injection at the seat and the stem. Injectable sealants may offer a temporary emergency seal.

Antic Static

A static charge is likely to build up on the stem and ball of a trunnion ball valve since they are suspended on non-metallic parts. An antistatic ball and metal spring are included in the design to maintain the metal-to-metal contact between the revolving stem or ball and the valve body, which aids in grounding the charges to the valve body.

Blowout Proof Stem

The trunnion valve stem is designed with a shoulder at the bottom. If the branch accidentally blows out under specific working conditions, it is held by the filling box.

Fire-safe design

The trunnion ball valve design is tested and certified fire-safe, thus preventing fire spread and environmental pollution. It has to be API 607 or API 6FA compliant.

What Are the Different Kinds of Trunnion Ball Valves?

Based on Body Configuration

Side Entry Trunnion Ball Valve

This design type is also called the split-body trunnion-mounted ball valve. It assembles its ball from the side. They are often made out of forged metal. In this design, the body is usually divided into three or two pieces joined together like extensions. A part of the body is often more significant than the rest of the design. This larger piece holds the stuffing that winds around the ball and itself. They are easy repairable and inspectable for this design because the smaller portion can be pulled out to reach the valve.

Top Entry Trunnion Ball Valve

This trunnion valve has a one-of-a-kind design that allows the ball to be assembled from the top. They are primarily composed of casting metal.

The ball valve has a removable bonnet cover that rests on top of it. By just removing the hood, the interior components are easily accessible. The valves are simple to disassemble and reassemble. The trunnion ball valve can be serviced and repaired by removing it from the pipeline.

Welded Body Trunnion Ball Valve

This design is primarily intended for gas transmission in subterranean pipelines. They come in greater sizes of up to 60 inches. They have ASME 900 psi medium pressure classifications. Centrifugal casting or forgings can be used as RAM materials in the design. They are made of various materials, including martensitic SS and carbon steels. The valve’s major technical features include an anti-blowout stem and a valve seat design accessible in three different design patterns:

  • DPE (Double Piston Effect): here, the seat may be energized by either upstream or body cavity pressure.
  • SPE (Single Piston Effect): In this design, the heart can be energized by upstream pressure and no other.
  • DUAL (SPE upstream and DPE downstream) combines the abovementioned two-seat designs. A double blockade can be guaranteed in case of seat-sealing failure.

Based On Bore

Full Bore

In the case of full-bore trunnion ball valve design, the diameter of the bore aligns with the connected pipeline. When the valve opens, the medium can flow without hindrance from the bore. They are helpful in areas or plants where pigging is needed.

Reduced Bore

A reduced bore valve is one with a bore size less than the diameter of the linked pipeline. The channel’s flow path is limited, resulting in greater energy loss. They apply to the gas and oil industry.

Based on the Sealing Material

A ball valve comprises two seat styles: soft seated and metal seated. Soft seat trunnion ball valves are installed using a thermoplastic material such as PTFE and Devlon. Metal seated ball valves use metals as seat materials like Inconel and Hastelloy.

Soft seat 

Soft chairs are often made of thermoplastic materials such as PTFE. They are great for environments where chemical compatibility and the tightest seal are essential.

Soft seats, on the other hand, should not be used in dirty or abrasive liquids. Soft seats may fail under these conditions, causing the valve to leak.

Metal Seat

The main difference between metal seated valves and soft seated trunnion ball valves is their ability to survive high temperatures and harsh service conditions. They can withstand severe hydraulic shock, flashing, abrasive process fluid, and higher temperatures above 1,000 ° F. They are also appropriate for high corrosion or erosion applications.

Based on Body Structure

Two Pieces Split Ball Valve

This valve is comprised of two casing sections connected by threaded connections. To reach the valve for maintenance or cleaning, one section of the casing can be readily opened. However, the valve must first be disconnected from the pipeline before the covering can be fitted.

Three pieces split the ball valve

The three-piece trunnion ball valves outperform the two-piece variant. They have three bolted-together casing parts. Remove one portion to gain access to the inside of the valve for maintenance and repair. To remove the valve for repair, however, there is no need to detach it from its pipeline.

Based on Body Material

Forged Ball Valve

A ‘forging’ procedure is used to create forged steel trunnion ball valves. Forging is based on the application of heat energy to solid steel blocks, followed by the use of mechanical forces to further convert the steel into a completed product. This method is used to make valves that are extremely sturdy and long-lasting. Mining and mining processing, agriculture and livestock handling, aeronautics, automotive industry, brickworks, stormwater plants, rendering plants, asphalt plants, power and water industries, pharmaceuticals, chemical industry, cosmetics industry, and other industries use SIO Forged Steel Valves.

Casting Ball Valve

Casting is a type of injection molding in which molten liquid metal is poured into a prepared mold. It forms castings after cooling. Casting can be classified technically as sand casting, pressure casting, investment casting, shell casting, casting without a cavity, casting with low pressure, casting with gravity, and so on.

Valve casting means that the parts, including the frame and bonnet, are cast. Casting, as opposed to forging, uses liquid metal to create valves. Casting produces valves with various sizes, patterns, and shapes.

Trunnion Ball Valve

Where is the Trunnion Ball Valve Used?

Trunnion ball valves are extremely adaptable. Because of their adaptability, they are employed in a wide range of sectors. The Trunnion Mounted Ball Valve, for example, has O-rings and fire-safe stem packs to prevent leaking. It also has stainless steel seal injection fittings for the emergency stem or seat. Ball valves with trunnion mounting are common in the chemical, petrochemical, oil and gas, LNG, and hydrocarbon industries.

They’re also employed in skids like turbines, compressors, generators, and separators, as well as field gas, polymer, LNG, crude oil, and industrial gas processing facilities, tank farms, automated process applications, hydrocarbon processing, and oil refinery feedstock lines. Trunnion ball valves are ideal for high-pressure, compact, low-temperature applications on a large scale.

Specific applications include:

  • Air, gaseous, and liquid applications
  • Cooling water & feedwater systems
  • Steam service
  • Instrument root valves

Why and How Should Trunnion Ball Valves Be Maintained?

It is critical to maintain the optimal performance of Trunnion ball valves. This is why it is critical to maintain all valves. Trunnion ball valves can be used in installations for considerably longer if they are well-maintained.

While soft seated valves provide the benefits of a quarter turn, they are only suitable for clean service. Because the bulk of the service is not completely clean, maintenance options are available. As seen in the case of trunnion ball valves, the use of emergency sealant injection frequently attracts debris to the seat, causing severe damage.

Flushing is Necessary

In order to facilitate cleaning, a flushing agent must be applied. Continuous lubrication of moving parts is necessary to prevent rust and wear and tear.

The Trunnion mounted ball valve ensures that the sealant injection facilities have the correct internal control valves and that the valve is fitted with body, ventilation, drain fittings, packing injectors, and lift lines, if necessary. The injection of synthetic lubricants into the seat and seal area allows the leaky seat to be sealed in an emergency.

The soft seat inserts might be harmed by even trace amounts of contaminants trapped in the fabric.

As mentioned above, flushing agents should be used to remove grease from the seating area, which may cause more harm to the seat as more debris is attracted.

Construction material left in the line will wreak havoc on soft seated valves by contaminating upstream parts. Before turning a soft seated valve, the line should be purged of nitrogen. The valve torque can be reduced by up to 40% by injecting sealant into the seating region, and many operators prefer to keep the synthetic lubricant in the seating area for this reason.

Repairs and Spraying are Crucial

Spraying is another maintenance method for the Trunnion ball valve. Leaving contaminants on the valve seat will improve torque by 80%. This makes emergency shutdown and functional valves more difficult.

To keep plants working efficiently, continuous inspection and maintenance are essential. Always seek the advice of an inline valve repair professional since there are numerous scenarios depending on the operation, size, class, and design of the system in use.

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