News/Blog
News/Blog
01, 1970
In the realm of valves, ball valves are renowned for their compact, robust design and dependable on/off control. They employ a spherical ball with a centrally drilled hole (port) to regulate media flow. Rotating the ball 90 degrees aligns the port with the valve body, allowing media to pass through. Rotating it back 90 degrees closes the valve. All ball valves rely on two seats, typically made of polytetrafluoroethylene (PTFE), to hold the ball in place and create a tight seal, preventing media leakage.
Floating ball valves are the predominant type used in industrial piping systems. These valves are designed so that as the seats wear, media pressure forces the ball against the downstream seat, maintaining a tight seal.
Trunnion ball valves feature a ball fixed in place by bearings, preventing it from drifting downstream. A spring-loaded seat mechanism ensures the valve remains leak-tight even as the seat wears down.
In this post, we delve into the details of floating ball valve design, explore their applications, and discuss scenarios where choosing trunnion-mounted valves might be advantageous.
Before delving into the specifics of floating ball valve design, it's important to understand the key components:
- Valve Body: The enclosure housing the valve mechanism, typically made of steel, iron, brass, bronze, or PVC.
- Ball: A spherical element with a central flow path, connected to the valve body via a stem or shaft.
- Bore or Port: The hollow center of the ball through which media flows.
- Packing: Flexible seals surrounding the valve stem to prevent media leakage from the valve body.
- Seat: A circular disc forming a seal between the valve body and the ball.
- Stem: The shaft securing the ball and linking it to an external operating lever or actuator.
- Actuator: An external device rotating the valve stem, which can be a lever, gear, electric motor-operated gear (electric actuator), or pneumatic/hydraulic actuator.
Most ball valves in use today are of the floating type. Floating ball valves feature cupped seats that tightly seal between the valve body and the ball. The ball itself is suspended within the media it controls and is held in place by cup-like seats, typically made of thermoplastics. These seats ensure a secure seal between the ball and the valve body.
Floating ball valves offer bi-directional sealing capability, allowing the ball to stop media flow in either direction. This type of valve is lightweight, cost-effective, and versatile, making it suitable for applications across industries such as oil, gas, water, steam, and petrochemicals.
Floating ball valves operate via a stem attached to the top of the ball, rotating it 90 degrees (a quarter turn). This rotation either opens or closes the port within the valve body, allowing or stopping the flow of media. The stem is loosely connected to the ball, allowing the ball to rotate on its axis. As media flows through, the pressure pushes the ball against its downstream seat, forming a tight seal.
In very low-pressure applications, after significant seat wear, floating ball valves may not seal as effectively because insufficient media pressure can prevent the ball from tightly sealing against the downstream seat. However, in most applications, downstream pressure is adequate to maintain a tight seal even as seats wear over time.
Trunnion ball valves operate similarly to floating ball valves, but with a critical distinction: the ball is anchored by a second stem opposite the operating stem, known as a trunnion.
In contrast to floating ball valve designs, the stem of a trunnion ball valve is firmly connected to the ball, restricting its movement to the axis. This feature prevents the ball from "floating" downstream under media pressure, enabling trunnion ball valves to maintain a secure seal on both sides simultaneously. This capability is particularly advantageous for multi-port valves and applications with very low media pressure, where the flow isn't strong enough to press the ball against its downstream seat.
Trunnion valves are effective in a wide range of pressures, from low to high, and they require less torque to operate compared to floating ball valves. However, it's important for piping system designers to consider that trunnion ball valve designs generally incur higher costs than floating ball alternatives.
Trunnion valves are common in the following industries:
Chemical
Electrical
Oil and gas
Pipeline
Hydrocarbon
In both floating and trunnion ball valves, the seal between the valve stem and the external environment is subject to the most wear and tear over time, so valve packing is a critical component in preventing media from escaping the piping system through the valve. It’s also recommended that piping system designers choose a spring loaded packing design to compensate for inevitable wear and prevent stem seal leaks.
