What is floating type ball valve?
Floating ball valves can be divided into two categories: side-mounted body and top-mounted body according to the structural form of the valve body. The side-mounted valve body can be divided into integral, two-piece, and three-piece types. No matter what kind of structure, they must meet some basic principles.
The basic principles that must be met by a floating ball valve are as follows：
①Stem should be installed backward, anti-blowout structure. This is ANSIB16.34 section 220.127.116.11, the structure of the valve stem should not rely on the packing gland fasteners to limit its position, to be precise, in the valve under pressure, the stem will not be due to the release of the stem sealing fasteners from the valve. This is the basic condition that must be ensured from the perspective of the safe use of the valve.
② anti-static structure is composed of a stainless steel ball and a spring, a group placed in the hole at the end of the stem to maintain contact with the ball; another group placed on the cylinder of the stem to maintain contact with the valve body so that the possible static electricity generated from the valve body guide away.
③ fire safe (fire-safe) structural design, the main and secondary valve body when the tetrafluoro plastic seal seat burned due to fire, should be in contact with the ball, and maintain a certain degree of sealing; main and secondary valve body connection surface should be used with fire-safe gaskets, such as metal winding gaskets; in the stem packing seal, when the packing (PTFE) is burned, there should be a graphite ring to stop the media leakage to the outside. The gasket should have a graphite ring to stop the medium from leaking out.
④There should be a limit mechanism to accurately limit the ball in the “open” or “closed” position.
⑤ There should be a platform for installing a pneumatic, electric, and worm gear actuator bracket on the valve body.
Structural design of integral valve body：
The figure below shows the structural design of the integral valve body, the stem is installed upside down, and there is a set of gaskets in contact with the valve body, consisting of two PTFE gaskets and one graphite gasket, to achieve friction reduction and misfire safety. The two lip seals are mounted with the ball from the side, and a threaded side cover is screwed from the side with a gasket placed between them to form a complete pressure boundary. The stem packing is made of herringbone PTFE for general purpose ball valves, which is pressed by the packing gland and bolts and nuts. The valve body has a platform for the mounting bracket, set “open” and “closed” position limiting mechanism, the mechanism has a hole for locking. The advantage of this structure is that the valve body is a monolithic structure, without the disadvantages of slack flange bolts, leakage, light weight, lower cost, suitable for Class150, Class300 and Class600, the diameter of 4in below the floating ball ball valve.
Structure of split body two-section floating ball ball valve：
The figure below shows the body construction of a split body two-part floating ball valve, which is the most common form of floating ball valve construction. The two-part valve body consists of a main body and a secondary body, bolted together, with a misfire-safe wound gasket of metal and PTFE in the middle. The effective cross section of the middle flange bolts should be larger than the effective cross section of the bolts on the flange connected to the pipeline and meet the requirements of ANSI B16. 34 standard to prevent the valve from slackening of the flange bolts due to external loads and temperature stresses in use. This most commonly used construction for Class150 and Class300, NPS 8 or less floating ball valves.
Split three-stage valve body structure of floating ball ball valve：
The figure below shows a split three-section body construction floating ball ball valve. There is a special series for this body construction up to NPS 4, which is discussed below.
The valve body is a monolithic structure, the upper openings have good rigidity, and the face of the seal seat is two beveled surfaces with a 3 ° inclination, the ball and the seal seat are composed of the upper loading, in order to make the seal seat and the ball assembly has a 3 ° inclination of the beveled surface, the centerline of the ball channel deviated from the center of the ball, also
There is a 3 ° inclination angle. The ball and stem can be provided with a spring between the ball and the bonnet to increase the preload of the seal seat. The advantage of this structure is that it can be repaired online, but the disadvantage is that the overall weight is large, the process is complex, and the cost is high. For the floating ball structure is suitable for Class150, Class300, Class600, the size of the passage NPS8 or below.
TAG: ball valve, floating ball valve, floating type ball valve, wesdom, wesdom valve