Why can not a ball valve regulate the flow rate?

A ball valve is a "rotary motion valve" whose core component is a ball with a through hole in the middle. When the through hole of the sphere is aligned with the axis of the pipeline, the valve is in a fully open state; When the ball is rotated 90 degrees so that the through-hole is perpendicular to the pipe axis, the valve closes completely. This simple opening and closing mechanism makes ball valves ideal for "quick shut-off of fluids".

Although ball valves can theoretically achieve flow control through partial opening, this approach has various problems and limitations in practical industrial applications:

1. The flow characteristics are non-linear and difficult to control accurately

There is a highly non-linear relationship between the flow rate and the opening of the ball valve. At the beginning of the opening (about the first 15 degrees of rotation), the flow rate increases very slowly; And at the middle opening (30-60 degrees), the flow rate rises sharply; Towards full opening, the flow rate changes flattened again. This non-linear nature makes it difficult for the operator to accurately predict and adjust the flow rate by handle position.

In contrast, specially designed control valves, such as V-ball valves or globe valves, have more linear flow characteristics and are able to provide smooth and predictable flow changes over the entire opening range, allowing for more precise control.

2. High-velocity fluids pose a risk of seal damage

When the ball valve is partially open, the high-velocity flowing medium will directly impact the sealed contact surface between the ball and the valve seat. This constant impact can lead to rapid wear and tear of the sealing material, especially the soft seal, and shorten the life of the valve. This is especially true in media containing solid particles, which can be carried by high-velocity fluids and cause abrasion damage to the sealing surface.

3. Cavitation and vibration problems

When a ball valve is partially opened under high differential pressure, a low pressure area may form behind the valve, resulting in vaporization of the liquid medium and bubbles. When these bubbles move with the fluid to a high-pressure area, they suddenly burst out, creating a strong shock wave, a phenomenon called cavitation. Cavitation can not only damage the internal components of the valve, but also cause vibrations in the piping system, threatening the safe operation of the entire plant.

4. Insufficient control accuracy

Standard ball valves lack accurate opening indication and positioning mechanisms, making it difficult for operators to accurately control the opening angle. Even when an electric or pneumatic actuator is installed, it is difficult to achieve high-precision flow regulation due to the nonlinear flow characteristics described above. In contrast, specially designed control valves, such as V-shaped ball valves or globe valves, are often equipped with a more precise positioning system and opening indication.