Trunnion Ball Valve - How It Works, Features, Applications, and More - SIO

How Does a Trunnion Mounted Ball Valve Work?

Home How Does a Trunnion Mounted Ball Valve Work?
08/08/2019
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Trunnion mounted ball valves are quarter-turn valves used to stop the flow of medium in pipelines. These valves feature a round or spherical disk in the center that rotates to start or stop the flow. This disk is called a ball and it features a hollow center. Ball valves are extremely versatile and are commonly used in industrial applications where tight shut-off is required.

Trunnion mounted ball valves feature additional support for the ball. This support is in the shape of a shaft and is called a trunnion. The trunnion absorbs any added pressure from the flow, reducing stress on the ball and seats of the valve. Trunnion mounted ball valves are used in high-pressure, large scale applications where low operating torque is required. 

How is a Trunnion Mounted Ball Valve Constructed?

Trunnion mounted ball valves have a similar structure as traditional ball valves. The only difference is that trunnion ball valves have additional mechanical anchoring that supports the ball or disk. In this design, the ball is supported from both ends on the x-axis, so that it stays in place and is easy to control. Here is a look at the different parts of a trunnion-mounted ball valve.

Tunnion mounted ball valve diagram

Body

The body of the valve is the casing that holds and protects the internal parts of a trunnion mounted ball valve. It can be made of carbon steel, stainless steel, low-temperature carbon steel, duplex, super duplex, Inconel, and more depending on the application. 

Stem

The stem of a trunnion mounted ball valve connects the ball to the actuator. It is connected to the ball through welded joints and it controls the movement of the ball. Trunnion ball valves have reinforced anti-blowout stems, that’s why they can handle cryogenic and high-temperatures without sustaining any damage.

Seats

The seats of a trunnion-mounted ball valve surround the ball. When the actuator is turned, the seats hold the ball snugly in place, sealing off any access. Trunnion ball valves have spring-loaded seats that move towards the ball as it is held firmly in place. 

Trunnion

In a trunnion mounted ball valve, there is an additional shaft that holds the ball in place from below. This small shaft is known as a trunnion and it keeps the ball firmly in place. In some ball valves, the trunnion is an extension of the ball while in others it is connected to the ball through welded joints.  

Disk

The disk in a trunnion mounted ball valve is in the shape of a perforated, solid ball. The ball is connected to the stem on one end and the trunnion on the other. In a trunnion ball valve, the ball or disk is held in place while it rotates. The seats are always in contact with the ball, hence reducing torque. 

Actuator

The actuator in a trunnion ball valve is used to open or close the valve. There are different kinds of actuators used in ball valves depending upon the application and medium. Bare stem, gear, hand lever, pneumatic actuator, and hydraulic actuator are some common actuators found on the valve. You can also use a gas actuator, gas-over-oil actuator, motor-operated actuator, hydraulic/electric actuator, hydraulic-operated actuator, and more. 

Types of Trunnion Mounted Ball Valves

Trunnion mounted ball valves are available in many different configurations. They are highly customizable so you can choose the size, type, and actuator that suits your needs. China also has the best trunnion mounted ball valve manufacturers for you to choose. Here are some common types of trunnion ball valves.

Based on Body Configuration

Body configuration determines how a valve can be accessed for maintenance or repair. There are two types of trunnion mounted ball valves based on body configuration.

Top Entry Trunnion Mounted Ball Valve

This type of ball valve has a removable bonnet cover on the top of the valve. The internal parts of the valve can be easily accessed by removing the bonnet. These valves are easy to assemble and disassemble. You can repair or maintain different parts of the trunnion valve without removing it from the pipeline. 

Top entry trunnion mounted ball valve

Source: SIO Top Entry Trunnion Mounted Ball Valve

Side Entry Trunnion Mounted Ball Valve

Side entry ball valves are also known as split body trunnion mounted ball valves. In these valves, the body is divided into two or three pieces that are bolted together like flanges. One piece of the body is always larger than the rest. The larger piece holds the ball as well as the stuffing that goes around the ball. These valves are easier to inspect and repair as the smaller piece can be removed to access the valve. 

Side entry trunnion mounted ball valve

Source: https://hardhatengineer.com

Based on Bores

The bore of the valve is the hole that is found in the middle of the disk or ball. Trunnion mounted ball valves have two types based on bore size.

Full Port Trunnion Mounted Ball Valves

In full bore valves, the size of the diameter of the bore matches that of the connected pipeline. When the valve is open, the medium can flow freely without restriction through the bore. This type of ball valve is used in chemical, petrochemical, and refining industries. They are also used in applications where pigging is required. 

Half Port Trunnion Mounted Ball Valve

A half port trunnion valve has a bore size that is a few nominal sizes less than the diameter of the connected pipeline. The flow path of the medium is restricted which results in higher energy losses. Half port valves are mostly used in the oil and gas industry.

Based on Assembly

The body of the valve may have one, two, or three pieces connected together though welded joints. There are two types of trunnion mounted ball valves based on the number of pieces.

Two-Piece Trunnion Mounted Ball Valve

This valve features two pieces of housing that are connected to each other through threaded connections. It is easy to open up one piece of housing to access the valve for cleaning or repair. However, the valve has to be disengaged from the pipeline before the housing can be removed. 

Two-piece trunnion mounted ball valve

Source: SIO Two-Piece Trunnion Mounted Ball Valve

Three-Piece Trunnion Mounted Ball Valve

Three-piece trunnion mounted ball valves go one step ahead of the two-piece design. They have three pieces of housing that are bolted together. You can remove one piece to access the inner parts of the valve for repair and maintenance. But you don’t need to disengage the valve from the pipeline to do so. 

three-piece trunnion mounted ball valve

Source: SIO Three-Piece Trunnion Mounted Ball Valve

How do Trunnion Mounted Ball Valves Work?

Trunnion mounted ball valves are quarter-turn valves. This means you need to turn the actuator on a 90-degree angle to turn the valve on or off. Once the actuator is turned the ball rotates so that the bore faces the pipeline and medium can flow freely. Another turn of the handle moves the ball so that the bore faces away from the pipeline stopping the flow. 

For example, you have to regulate the flow of oil through a critical process unit. You will install a three-piece, half-bore, split-body ball valve like SIO Trunnion Mounted Ball Valve to get the job done. To start the flow of oil, you will move the actuator on the valve 90 degrees one way (usually clockwise). The actuator is connected to the stem of the valve which in turn is connected to the ball. As the stem rotates it moves the ball as well so that the side of the ball with the bore faces the pipeline. Since this is a half-bore valve the flow of oil is restricted, lowering the pressure with which the stream flows. 

SIO trunnion mounted ball valve

To stop the flow, you rotate the actuator again moving both the stem and the ball. The bore of the ball now faces away from the pipeline inhibiting flow. The upstream pressure on the valve pushes the seats closer to the ball so that they make a tight seal. Since the seats of a trunnion mounted ball valve are spring-loaded, even low pressures can push them against the ball. This tight seal stops the flow of oil and also prevents oil from getting into the internal parts of the valve. 

Trunnion mounted ball valves are used in both high-pressure and low-pressure applications. In high-pressure applications, the valve maintains its torque as any added pressure on the seats and ball is absorbed by the trunnion. In low-pressure situations, the valve’s spring-loaded seats move closer to the ball to form a firm seal.

What are the Applications of Trunnion Mounted Ball Valves?

Trunnion mounted ball valves are extremely versatile. They are used in many different kinds of industries because of their customizable features. For example, SIO Trunnion Mounted Ball Valve features O-rings and fire-safe stem packaging that prevent leakages. It also comes with stainless steel sealant injection fittings for emergency stem or seat sealing. Trunnion mounted ball valves are used widely in chemical, petrochemical, oil and gas, LNG, hydrocarbon industries. 

SIO trunnion mounted ball valve

Source: SIO Trunnion Mounted Ball Valve

They are also used for many different kinds of applications including skids like turbine, compressor, generator, and separator, field gas, polymer, LNG, crude oil, and industrial gas processing plants, tank farms, automated process applications, hydrocarbon processing, and oil refinery feedstock lines. Trunnion mounted ball valves are suitable for both large scale high-pressure applications and compact, low-temperature situations. 

What are the Advantages of Using Trunnion Ball Valves?

Trunnion mounted ball valves are very popular in the piping industry. That is because they can handle different kinds of applications and mediums including liquid, gasses, and slurries. Here are some of the most favorable advantages of using trunnion mounted ball valves.

No Size Limit

Trunnion mounted ball valves can be found in all kinds of sizes. Two and three-piece ball valves can house large sized balls so they are perfect for larger applications. Single unit trunnion mounted ball valves can be used for smaller, low-pressure applications. Since they can handle high-pressure operations, trunnion mounted ball valves are also suitable for critical operations.

Customizable Features

Trunnion mounted ball valves can have many value-added features. You can fortify the seats and the ball with injections to make them seal tightly. The bearings and bolts can be made corrosion-resistant increasing the valve’s longevity. Larger valves can be equipped with lifting lugs. 

Spring-Loaded Seats

The basic difference between floating ball valves and trunnion mounting ball valves is that the latter has spring-loaded seats. In a floating ball valve, the pressure of the onstream forces the ball to move towards the seats creating a seal. However, the ball needs high pressure to do so. This makes floating ball valves ineffective in low-pressure situations. In trunnion mounted ball valves the pressure from the onstream activates the spring-loaded seats so that they move towards the ball that is held in place by the trunnion. This creates a tighter seal and makes the valve efficient in both high and low-pressure situations. 

Ease of Operation

Any added pressure on the valve is absorbed by the trunnion and the stem. This means the valve needs a lower operating torque and a smaller actuator. This reduces costs and makes it easier to operate the valve. Three-piece trunnion mounted ball valves are also easy to repair, clean, replace, and maintain as you only have to remove one piece to access the working parts of the valve.

Double Block and Bleed Capabilities

One of the stand-out features of trunnion mounted ball valves is that they can have a double block and bleed capabilities. You can use multiple trunnions mounted ball valves to make a double block and bleed valve. Or add a bleed body to a two-piece or three-piece trunnion ball valve to help improve its sealing abilities. The double block and bleed function makes it possible to flush the valve under pressure and verify that the seats are sealing properly.

Conclusion

Trunnion mounted ball valves provide tight shut-off in larger, critical, high-pressure operations and specialized low-pressure applications. The seats of the valve are always in contact with the ball making for tighter seals that prevent leakages. SIO can help manufacture trunnion mounted ball valves that meet your requirements. Our trunnion valves have bolted a three-piece body that incorporates double O-rings or a combination of O-rings and gaskets, suitable for buried or above-ground installation. They also feature double piston, self- relieving seats with Inconel® seat springs. Contact us for more information on how we can customize your trunnion mounted ball valves.

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