Ball Valve – Learn about Floating and Trunnion Mounted Ball Valves
A Ball valve is a quarter-turn rotary motion valve that uses a ball-shaped disk to stop or start the flow. Ball valve resembles plug valve in many ways. When a port in the ball is in line, it allows flow whereas when you rotate the valve 90 degrees, solid part of the ball stop the flow.
Most ball valves are of the quick-acting type, which requires a 90° turn of the valve handle to operate the valve. But in case large size valve which required considerable force to open or close the valve, the gear-operated actuator is used. With this arrangement, a small handwheel is enough to operate a fairly large valve.
Ball Valve Parts
Major components of the ball valve are the body, spherical ball, steam, and seats. The ball valve can be metal seated or soft seated. A ball valve may be unidirectional, bidirectional, or multidirectional, depending on the number of valve ports and the number of valve seats. Same as multiport plug valve. In the image below, you can see the 3-way ball valve.
3 Way Ball Valve
Depending on your requirement, you can arrange the port of the 3-way ball valve in the three-way.
1. One inlet and two distribute
2. One inlet and one outlet with diverting a flow
3. Stright pass the fluid without No inlet
4. Three patterns are available in Ball Valves. Venturi port type, full port type, and reduced port type. The full-port ball valve has an inside diameter equal to the inside diameter of the pipe. This design allows pigging. In the venturi and reduced-port types, the port is generally one pipe size smaller than the line size.
5. Ball of the ball valve can be a free float or fixed in the valve body. A free floating ball valve is known as floating type whereas fixed type valve is known as trunnion mounted ball valve.
Floating Ball Valve
In floating ball valve, the ball is held in the position by the compression of the two elastomeric seats against the ball. The ball is free to float inside the valve body. See the highlighted portion in the image and remember as you will see the difference when I will explain you about trunnion mounted ball valve.
The stem is connected to a slot at the top of the ball which allows the ball to rotate a quarter turn (90 degrees). The shaft allows for a certain amount of lateral movement of the ball that is generated from the upstream pressure acting on the ball. This small lateral movement, in fact, produces a load on the ball that presses it against the downstream seat which improves leak tightness of valve. This type of ball valve design is, therefore, capable of bi-directional shut-off. Floating ball valve is very difficult to operate when upstream pressure is high. You can see the image of floating ball valve.
Trunnion Mounted Ball Valve
Trunnion mounted ball valve is a solution to the problem of excessive torque required by floating ball valve in high-pressure service. A short shaft like an extension that called trunnion set in the body. You can see this in the image. In this design steam and ball work as a single unit. The ball is supported by two floating or spring-loaded seats that remain in constant contact with the ball.
Trunnion ball design required a lower operating torque. Hence, reduces the size of the actuator and overall costs of the valve. This cost difference becomes an important factor when the pressure class and valve size increases.
Types of Ball Valves
Ball valves are manufactured in different body arrangements. Based on this valve can be classified in following ways;
§ Top entry
§ Side entry or split body
§ Three-piece body
For Extremely high pressure and temperature services, full welded body is also used.
Top-Entry Ball Valve
As you can see in the image above, removing bonnet cover of top entry ball valves, allows access to valve internals for assembly, disassembly, repair, or maintenance without removing the valve from the pipeline.
Split-Body Ball Valve
In this design, a valve body is divided into two or three body parts. A ball, seat rings, stem, and other internals set inside the larger body part and held together with smaller part by bolting.
For split body two pieces ball valve, refer floating ball valve image. Refer below image for split body three pieces ball valve.
Ball Valve Applications
§ It can be used in different types of fluid services as on-off stop valve that provides bubble-tight shutoff.
§ It can be used in air, gaseous, and vapor services as well as hydrocarbon services.
§ Metal seated valves can be used in high-pressure & temperature applications.
§ Ball valves are widely used with instrument tubing to connect instruments.
Ball Valve Advantages
§ It is Quick to open and close type that provides bubble-tight reliable sealing in high-pressure temperature applications.
§ It is Smaller and lighter than gate valve of same size and rating.
§ Several designs of ball valves offer the flexibility of selection so that you can choose the valve that suits your requirements.
§ Easy to operate and Cost effective maintenance.
Ball Valve Disadvantages
§ It cannot be used in service that required throttling.
§ In slurry or other similar applications, the suspended particles can settle and become trapped in body cavities causing wear, leakage, or valve failure.
§ Due to rapid opening and closing, surge pressures may arise which could damage downstream equipment.