How Do Floating Ball Valves Work?

Ball valves are renowned in the valve industry for their compact and durable design, as well as their reliable, quick on/off control. These valves feature a ball with a hole (or port) drilled through the center, which regulates the flow of media. By rotating the ball 90 degrees, the port aligns with the valve body, allowing the media to flow freely. To stop the flow, the ball is turned 90 degrees back to its closed position. Ball valves typically rely on two seats, often made of polytetrafluoroethylene (PTFE), to securely hold the ball and form a tight seal, preventing any leakage of media through the valve.

There are two main types of ball valve designs: floating and trunnion. Floating ball valves are the most widely used in industrial piping systems. These valves are designed in such a way that when the seats begin to wear, the pressure from the media flowing through the valve pushes the ball against the downstream seat, ensuring a tight seal is maintained.

In contrast, trunnion ball valves have a ball that is fixed in place by bearings, preventing it from floating downstream. A spring-loaded seat mechanism helps maintain a leak-tight seal as the seat naturally wears down over time.

In this post, we will explore the design of floating ball valves and their applications, as well as discuss when it might be better to choose a trunnion-mounted ball valve over a floating one.

Floating Ball Valve Design

Before we delve into the details of floating ball valve design, let’s first define the key components of a ball valve:

Valve Body – The outer chamber that houses the valve mechanism. Ball valves are typically made from materials like steel, iron, brass, bronze, or PVC.

Ball – A rotating sphere with a central flow path, connected to the valve body by a stem or shaft.

Bore or Port – The hollow center of the ball through which media flows.

Packing – Flexible seals around the valve stem that prevent media from leaking out of the valve body.

Seat – A round, donut-shaped disc that forms a seal between the ball and the valve body.

Stem – The shaft that holds the ball in place and connects it to the external operating lever or actuator.

Actuator – A device that rotates the valve stem. This could be a manual lever, a gear, an electric actuator (motor-operated), or a pneumatic/hydraulic actuator.

Most ball valves are of the floating type. Floating ball valves are supported by cupped seats that create a tight seal between the valve body and the ball. The ball is suspended within the media it controls, held in place by cup-like seats, typically made from thermoplastic materials. These seats ensure a secure seal between the ball and the valve body.

Floating ball valves are designed to provide bi-directional sealing, allowing the ball to move freely and stop media flow in either direction. These valves are lightweight, cost-effective, and versatile, making them suitable for a wide range of applications, including oil, gas, water, steam, and petrochemicals.

How Do Floating Ball Valves Work?

Floating ball valves are operated by a shaft or stem connected to the top of the ball, which rotates it 90 degrees (a quarter turn). As the ball turns, the port is either covered or uncovered by the valve body, controlling the flow of media. The stem is attached loosely to the ball, so as the ball rotates, the pressure from the flowing media pushes it against the downstream seat, ensuring a tight seal.

However, floating ball valves may struggle to seal effectively in very low-pressure applications after significant seat wear. This is because there may not be enough media pressure to push the ball against the downstream seat to create a proper seal. In most cases, though, the downstream pressure is sufficient to maintain a tight seal even after the seats start to wear.