Introduction to Ball Valves: Construction

Major components of a ball valve are valve body, valve bonnet, spherical closure member(ball), seats, stem, gaskets and bolts & nuts. Usually ball valves are manufactured in two patterns: full port and reduced port (also called “full bore” or “reduced bore”). The full-port ball valve has an inside diameter equal to the inside diameter of the pipeline. For reduced-port ball valve, the flow area of that port of the closure element(ball) is less than the area of the inside diameter of the pipeline. Stem sealing is accomplished by bolted packing glands and O-ring seals. Ball valves can also be furnished with a lubricant-seal system which is a common design in trunnion mounted design.

A ball valve may be unidirectional, bidirectional, or multi-directional, depending on the number of valve ports and the number of valve seats. Therefore, ball valves are referred to as 2-way, 3-way, 4-way, or 5-way multi-port valves. A 2-way ball valve with a single seat will be unidirectional with the flow direction indicated. Even a 3-way, 4-way, or 5-way ball valve can be unidirectional when flow must enter through a designated port. A 2-way ball valve provided with two seats, one on the upstream side and the other on the downstream side of the ball, is termed a bidirectional valve. Multiple-port ball valves permit flows in more than one direction, thus eliminating the need for several valves.

Ball valves can also be categorized as per its body construction: side entry, top entry, three-piece body, and split body. They can also be categorized as per end connection styles: RF flanged, RTJ flanged, Butt Welding (BW), Socket Welding (SW), andThreaded (NPT or BSPT), etc. There are also two most common ball valve categories according to its seating arrangements:floating and trunnion mounted. For floating type ball valve, the ball is not fixed to the stem and is allowed some freedom of movement through the key slot. On other hand, if the ball is fixed at two pivot points of the stem, it is called trunnion mounted.

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Views: Author：hbmetals Date:15/04/02