Compared with gate valve, globe valve and check valve design, the history of ball valve is much shorter. Although the first ball valve patent was issued in 1871, it will take 85 years for the ball valve to be commercially successful. Polytetrafluoroethylene (PTFE, or “Teflon”) was discovered during the process of designing the atomic bomb during World War II, which will become a catalyst to start the ball valve industry. Ball valves are available in all materials from brass to carbon steel and stainless steel to zirconium.

There are two basic types: floating balls and trunnion balls. These two designs allow the construction of effective ball valves from ¼” to 60” and larger. Generally, the floating design is used for smaller and lower pressure valves, while the trunnion type is used for larger and higher pressure valve applications.

VM SUM21 BALL API 6D ball valve API 6D ball valve uses these two types of ball valves because of their sealing methods and how the fluid force flows from the pipeline to the ball and then distributes to the valve seat. In the floating ball design, the ball fits tightly between two seats, one upstream and one downstream. The force of the fluid acts on the ball, pushing it into the valve seat located in the downstream valve body. Since the ball covers the entire flow hole, all the force in the flow pushes the ball to force it into the valve seat. If the ball is too large and the pressure is too large, the force on the valve seat will be large, because the operating torque is too large and the valve cannot be operated.

Floating ball valves have a variety of body styles, but the most popular is the two-piece end inlet type. Other body styles include three-piece and top entry. Floating ball valves are manufactured in sizes up to 24″ and 300 grades, but the actual application range of floating ball valves is usually much lower-the maximum is about 12″.

Although ball valves are primarily designed as on/off or “stop” valves, the addition of some ball valves and V-port ball valve designs makes them ideal for controlled applications.

Elastic seat
VM SUM21 BALL Flanged Ball Valve Flanged ball valve Smaller floating ball valves can be used in many different applications, from household pipes to pipes containing the most demanding chemicals. The most popular seat material for these valves is some form of thermoplastic, such as PTFE. Teflon valve seats work well because they are soft enough to seal well on polished metal balls, but strong enough to not blow out of the valve. The two main problems with these soft seat valves are that they are easily scratched (and potentially leaking), and the temperature is limited to below the melting point of the thermoplastic seat-around 450oF (232oC), depending on the seat material.

A feature of many elastic seat floating ball valves is that they can be properly sealed in the event of a fire that causes the main seat to melt. This is called a fireproof design; it has a seat pocket that not only holds the elastic seat in place, but also provides a metal seat surface that provides a partial seal when it comes into contact with the ball. According to the American Petroleum Institute (API) 607 or 6FA fire test standards, the valve is tested to confirm the fire protection design.

Trunnion design
VM SUM21 BALL API 6D trunnion ball valve API 6D trunnion ball valve When a larger size and higher pressure ball valve is required, the design turns to the trunnion type. The difference between the trunnion and the floating type is that the trunnion ball is fixed in the main body by the bottom trunnion (short connecting rod) and the top rod. Since the ball cannot “float” into the valve seat to achieve a forced closure, the valve seat must float on the ball. The design of the trunnion seat causes the seat to be stimulated by upstream pressure and forced into the sphere for sealing. Because the ball is firmly fixed in place, except for its 90o rotation, the extraordinary fluid force and pressure will not jam the ball into the valve seat. Instead, the force only acts on a small area outside the floating seat.

VM SUM21 BALL End inlet design The end inlet design trunnion ball valve is the powerful big brother of the floating ball valve, so it can handle big jobs-high pressure and large pipe diameters. By far, the most popular use of trunnion ball valves is in plumbing services.