Some confusion still exists concerning the proper terminology for this valve. The circumstances causing this are that the valve is basically a member of the plug valve family, and that the term 'ball valve' is frequently used when referring in fact to the ball float operated valve. Names such as 'spherical plug valve' and 'ball plug valve' are still sometimes used but the simple term 'ball valve' has now become dominant and will be used here.
The ball valve is an adaptation of the plug valve. It has the same 90° rotary movement and the rotary mem-ber is in constant contact with the seats. The plug is in the form of a ball with a circular hole or flow way through one axis. The proportions of the ball and flow way are such that when the ball is given a quarter turn a full spherical face is presented to the inlet and outlet ports of the valve, thus shutting off the flow.
Ball valves offer positive tight shut-off with a quarter turn operation and low operating torque. Full parallel bore valves provide straight through flow with a minimum of resistance and even with reduced bore valves the pressure drop across the valve is still extremely small. Consequently, and for economic reasons, the majority of ball valves today have a reduced bore through the ball, the most common exception to this being when some form of 'pigging' of the pipeline is required.
Ball valves are generally considered to be most suited for straight on-off duties but recent developments have introduced ball valves specially designed for throttling and flow control.
An important aspect of the ball valve is the inherent compactness of the design, making for easy handling and maintenance.
Most standard ball valves have an operating temperature range of between -30 °C and 230 °C at pressures from a coarse vacuum (25 torr) to 51 bar, depending on size. Specialized valves are available, however, for services below -200 °C and above 500 °C and from very high vacuum (10-9 torr) to above 400 bar.
The applications of ball valves are as wide and varied as industry itself. They range from simple services such as water, solvents, acids, and natural gas to more difficult and dangerous services such as gaseous oxygen, hydrogen peroxide, methane, and ethylene. Limitations of use are governed by the temperature and pressure characteristics of the seat material, but research and development of new materials make it foreseeable that the future will see an extended use of the ball valve for an even wider range of applications than at present.
Ball Valve Body Types
These may be divided into one-piece bodies and multipiece bodies and Actuation Valve provide all of the variations available.
The one-piece body type provides a very rigid construction. In the top entry version, it is possible to remove the ball and seats from the valve without taking the valve out of the line, an advantage where maintenance in-situ is permitted and where valves are welded into the line. The one-piece body with end entry provides a compact design which dispenses with the need for a body joint, hence eliminating a potential leak path. Here the valve must be removed from the pipe line to obtain access to the working parts. This can be an essential requirement in some industries where it is often forbidden to do maintenance in-situ.
Multi-piece bodies, two-piece or three-piece (sandwich), offer greater scope for ingenuity of design. For example, in the sandwich type, the central portion containing all the working parts can be removed as a unit from the valve, leaving the two body end connectors in position in the line. Again, this is useful in the case of welded ends and it also makes possible the provision of interchangeable end connectors.
Ball Valves Seating Materials
Although ball valves with all metal seats are used on certain applications, the most general seating combination is a metal ball contained between plastic or elastomer seatings. Polytetrafluorethylene (PTFE), either virgin or 'filled', is commonly used for seats but a number of other materials are used from time to time for particular applications. These include nylon, 'Buna N', graphite and PCTFE.