Trunnion Ball Valve – How They Work
Trunnion ball valves are quarter-turn valves used to stop or start the flow of a media in a pipe. The most common type of ball valve has a “free floating” design, so the trunnion type is a design change. Within a trunnion ball valve the ball connects to the stem on one end and on the other end a shaft called the trunnion. Due to this design change, the ball is held firmly in place. In a floating ball valve, the ball is only connected to the stem, and is therefore called floating. This is illustrated in Figure 1 and highlighted by a red box.
Trunnion ball valves have many different advantages over free floating valves, they are suitable for low, and high-pressure applications, and offer lower operational costs then free floating ball valves. Learn more about ball valves in our extensive ball valve guide.
Trunnion ball valve advantages
High pressure applications
For high pressure applications, a trunnion ball valve is the ideal ball valve design type. In the floating ball valves the ball has some freedom of movement. During use, the ball floats slightly downstream against the seat ring and creates a sealing only on one side of the valve. In addition, the torque on the stem is also increased.
This is the point where the trunnion design offers a solution. In the trunnion valve design, the ball is not floating as it is connected to the trunnion. This is advantageous since it will maintain a proper seal on both sides and there is no added torque to the stem. Therefore, for higher pressure applications a trunnion ball valve will provide better sealing and require less torque to turn.
Spring-Loaded Seats
Trunnion mounted ball valves are fitted with spring loaded seats. In a floating ball valve the pressure forces the ball against the seats, which creates a seal. Unfortunately the ball valve will need high pressure to create an effective seal, which would render them ineffective in low pressure systems.
Trunnion mounted ball valves are effective in both low and high pressure situations. In low or no-pressure situations the spring-loaded seats will create a seal, while also working for high pressure applications.
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Lower operational costs
A trunnion mounted ball valve provides lower operational costs due to the fact that any additional pressure on the valve is absorbed by the trunnion and the stem. This leads to a lower operating torque, and subsequently eliminates the need for a large actuator.
To learn more about making the right selection of ball valve for your application, read our ball valve selection technical article!
Applications
Trunnion ball valves are popular due to the ability of being customized to a wide variety of uses, however they are most commonly used in the following industries:
- Chemical Industries: Because trunnion mounted ball valves offer a safe and durable seal, these are used in a wide variety of chemical applications where such attributes are deemed vital.
- Electrical Industry: Trunnion mounted ball valves can be used in various applications such as turbines, skids, generators, and compressors which are important to the operation of power industries.
- Oil and gas industry: Oil and gas industries that use trunnion mounted ball valves include field gas plants, oil refinery feedstock lines, gas feed lines, crude oil plants, and industrial gas processing plants.
- Pipeline industries: The ability to handle several different media such as gasses, slurries, and liquids make trunnion ball valves extremely valuable to the pipeline industry.
- Hydrocarbon industries: Trunnion mounted ball valves are extremely useful for hydrocarbon processing.
>>>>> What is the difference between a trunnion ball valve and floating ball valve?
The ball in a trunnion ball valve is supported by the stem and trunnion, reducing the operating torque, while the seats are spring loaded. In a floating ball valve, the ball floats and the seats are fixed while the ball is only supported by the stem.
What is a trunnion ball valve?
A trunnion ball valve is a quarter-turn valve which has a ball supported by both the stem and trunnion, giving it greater strength and a reduced operating torque.
How does a trunnion ball valve work?
In a trunnion ball valve the ball itself does not move towards the seals, rather the seals move towards the ball due to spring loaded seats. In a floating ball valve the ball moves towards the seats. This gives trunnion ball valves a greater operating strength, better ability to handle pressure, and a lower operating torque.
What is trunnion mounted?
Trunnion mounted refers to how the internal ball of a ball valve is mounted. The ball is supported by protruding shafts.