We are now talking about the sealing principle of floating ball valves and fixed ball valves.
The opening and closing part of
floating ball valves is a ball. The middle of the valve has a pipe diameter equal to the hole. The end of each inlet end and outlet is with a PTFE sealing seat. It is contained in a metal valve body. When the ball body through hole and pipeline channel coincide, the valve is in open state. The valve is closed when the through-hole in the ball body is perpendicular to the line passage.
The sealing principle of ball valves
When the valve is in the closed position, the inlet end of the medium force is on the sphere. It will make the geometric center of the sphere produce a small displacement, and the outlet end of the seat close contact, increasing the contact stress on the sealing belt, so as to obtain a reliable seal. The pretightening force of the valve seat at the inlet end contacting the sphere will decrease, which will affect the sealing performance of the inlet sealing seat. The floating ball valve only has the export end of the sealing seat to play a sealing role, and the inlet end of the sealing seat and the ball to maintain a small floating gap.
Floating ball valves
When the ball valve is in the closed position, and the import pressure effect is on the sphere, the media produce a force pushing sphere. It forms a contact zone and contact force per unit area called the valve sealing work pressure. When the pressure is greater than the seal required for specific pressure, the valve is effectively sealed. This sealing method is not by external force. It is sealed by medium pressure, which is known as medium self-sealing.
The sealing principle of ball valve is the force acting on the sealing seat, produced by the pressure of the medium. This force is stable and controllable.
The opening and closing part of fixed ball valves is a sphere with two supporting shafts. There is an equal channel and pipeline size, flanked by two floating seats. The sphere rotation does not stray from the axis of the ball bearing shaft. The supporting shaft is supported by two sliding bearings. The seat is floating. The medium is under the action of force, to the sphere to create a contact stress.
Fixed ball valves
The fixed ball valve is composed of the main body, left vice valve body and right vice valve body. The sphere is a top journal. The upper body has a stuffing box, and a sphere axis neck is through a sliding bearing. The ball bottom has a shaft hole and a sliding shaft bearing. There is a bearing in the shaft hole of the bottom of the sphere at the bottom of the valve body. In this way, the sphere is kept on the centerline of rotation without deflection. There are two floating seat assemblies symmetrically on both sides of the sphere. The seat assembly consists of a metal seat ring, a PTFE seal ring embedded in the seat ring, a rubber O-ring on the outer edge and a spiral spring on the back. When the valve is closed, the medium force acts on the components of the sealing seat. It makes the seat contact with the sphere, resulting in contact stress, in order to obtain an effective seal. Stem and packing boxes are sealed by o-rings.
The fixed ball valve is mainly used in high-pressure large diameter ball valves. The same is the principle of media self-sealing, but the medium force of fixed ball valves is acting on the annular area of the seat. The operating torque is also smaller than that of the floating ball valve, but the structure of the fixed ball valve is much more complex than that of floating ball valves. The weight is large. The price is more expensive than that of floating ball valves with the same specifications. Fixed ball valves can be designed with full-sizes, standards and reduced sizes for greater flow capacity and lower flow resistance coefficient.
