There are significant differences between floating ball valves and fixed ball valves in terms of structure, working principle, applicable working conditions and sealing performance.
1. Structural differences
Floating ball valve:
The ball is not supported by a supporting shaft and is supported only by two valve seats.
The valve stem is movably connected to the ball, so that the ball is in a "floating" state.
Usually only one lower valve stem is connected to the ball, and the upper valve stem generally only plays the role of transmitting torque and is not directly fixed to the ball.
Fixed ball valve:
The ball is fixed in the valve body and does not move with the medium pressure.
The ball is fixedly connected to the valve body through the upper and lower valve stems and cannot move freely.
The upper and lower valve stems are firmly connected to the ball, which jointly restricts the movement of the ball so that it can only rotate.
2. Working principle
Floating ball valve:
The valve stem is driven by a handle (or other drive device), and the ball can rotate freely between the two valve seats.
When the through hole of the ball is aligned with the channel hole of the valve body, the ball valve is in an open state and the fluid flows.
When the ball rotates 90° and the ball through hole is perpendicular to the valve body channel hole, the ball valve is in a closed state. At this time, the ball is pushed to the valve seat on the valve outlet side under the action of fluid pressure to achieve valve sealing.
Fixed ball valve:
Control the on and off of the medium by rotating the ball.
When opening and closing, the ball rotates around its fixed axis.
The sealing performance depends on the preload between the ball and the valve seat and the transmission of the valve stem.
Three, applicable working conditions
Floating ball valve:
Mostly used in low-pressure, small-diameter pipeline systems.
Applicable to occasions with high requirements for medium cleanliness and relatively stable medium pressure, such as water supply and drainage systems, air conditioning systems, etc.
Not suitable for high temperature and high pressure environments, because the sealing surface material limitation limits the use of floating ball valves in high temperature and high pressure environments.
Fixed ball valve:
Mostly used in high-pressure, large-diameter pipeline systems.
Applicable to occasions with high requirements for sealing performance and flow control, such as key pipeline systems in industries such as petrochemicals, natural gas transportation, and power.
Able to withstand higher pressure, small torque, small seat deformation, stable sealing performance and long service life.
4. Sealing performance
Floating ball valve:
Rely on the medium pressure to push the ball to the outlet valve seat to achieve sealing.
The greater the medium pressure, the better the sealing effect. However, at low pressure or no medium pressure, the ball may not fit tightly with the valve seat due to its own weight and other reasons, and the sealing performance may be affected to a certain extent.
Fixed ball valve:
Through the preload between the ball and the valve seat and the transmission of the valve stem to achieve a tight fit and seal.
Regardless of the medium pressure, its sealing performance is relatively stable and is not affected by medium pressure fluctuations.
Some fixed ball valves also have a middle cavity pressure relief function. When the middle cavity pressure rises abnormally, it can automatically relieve pressure to ensure the safe use of the ball valve.
