Floating ball valve sealing principle.
Floating ball valve opening and closing parts is a sphere, the middle of a through-hole equal to the diameter of the pipeline, the inlet and outlet ends are placed in a PTFE seal seat, and is contained in a metal valve body, when the hole in the ball and the pipeline channel overlap, the valve is in the open state; when the hole in the ball and the pipeline channel vertical, the valve is in the closed state. Valve from open to close, or from close to open ball rotation 90 ° angle of travel.
Floating ball valve sealing principle
When the ball valve is in the closed position, the media pressure at the inlet end acts on the ball, resulting in a force that pushes the ball, so that the ball presses against the seal seat at the outlet end, resulting in contact stress on the conical surface of the seal seat, forming a contact zone, the contact zone unit area of The force per unit area of the contact zone is called the working pressure q of the valve seal, and when this pressure is greater than the pressure necessary for sealing, the valve is effectively sealed. This type of sealing is not by external force, sealed by the pressure of the medium, is called media self-sealing.
It should be noted that traditional valves such as globe valves, gate valves, midline butterfly valves and plug valves rely on externally applied forces acting on the gate seat to obtain It should be noted that traditional valves such as globe valves, gate valves, midline butterfly valves and plug valves rely on external force applied to the gate seat to achieve a reliable seal.
The externally applied forced sealing force is It is not conducive to the long-term use of the valve because of its arbitrariness and uncertainty. The sealing principle of ball valves is the force acting on the seal seat, generated by the pressure of the medium. This force is stable and controllable, and is determined by the design.
①In order to ensure that the ball in the closed position, can produce a medium force, prior to the valve assembly, the ball must be close to the seal seat, and the need for interference, resulting in a preload ratio pressure, the preload ratio pressure of 0.1 times the working pressure and not less than 2MPa. this preload ratio pressure obtained, relying solely on the design of the geometry to ensure. If set the ball and inlet, outlet seal seat after the combination of the free height of A; left and right valve body after the combination of the cavity to accommodate the ball, the width of the seal seat B, the assembly to produce the necessary preload than the pressure required for the interference C, must meet: A – B = C. This C value must be guaranteed by the geometry of the parts processing. It is conceivable that this interference C is difficult to determine and guarantee. The size of the interference value directly determines the sealing performance and operating torque of the valve.
②It should be especially noted that early domestic floating ball ball valves are often adjusted with shims due to the difficulty of controlling the interference value during assembly, and many manufacturers even refer to this shim as an adjustment pad in the manual. In this way, there is a gap between the connecting plane of the main and sub valve body during assembly, the existence of this gap, due to fluctuations in medium pressure and temperature fluctuations in use, as well as the role of external pipeline load, will make the bolt slack, causing external leakage of the valve.
③ When the valve is in the closed position, the media force at the inlet end acts on the ball, which will cause a slight displacement of the geometric center of the ball, and the outlet end seat close contact, increasing the contact stress on the sealing belt, so as to obtain a reliable seal; and the preload of the inlet end seat in contact with the ball will be reduced, affecting the sealing performance of the inlet sealing seat, this ball valve structure, which is in working condition, the ball Geometric center has a small displacement of the ball valve, called floating ball ball valve. Floating ball ball valve is the export side of the seal seat seal, the inlet side of the seat is not sure whether there is a seal function.
④The floating ball ball valve structure is bi-directional ( bi-direction), that is, both media flow direction can be sealed.
⑤The sealing seat where the ball meets is made of polymer material, when the ball rotates, static electricity may be generated, and if there is no special structural design-anti-static design, static electricity may accumulate on the ball.
⑥For the valve consisting of two sealing seats, the valve cavity may accumulate media, some media may be abnormally elevated due to changes in ambient temperature and use of working conditions, causing damage to the valve pressure boundary, should be noted.
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