What Is a Ball Valve?
A ball valve is a flow control device which uses a hollow, perforated, and pivoting ball to control liquid flowing through it. It is open when the ball’s hole is in line with the flow inlet and closed when it is pivoted 90-degrees by the valve handle, blocking the flow.
The handle lies flat in alignment with the flow when open, and is perpendicular to it when closed, making for easy visual confirmation of the valve’s status. The shut position 1/4 turn could be in either clockwise or counter-clockwise direction.
Ball valves are durable, performing well after many cycles, and reliable, closing securely even after long periods of disuse. These qualities make them an excellent choice for shutoff and control applications, where they are often preferred to gates and globe valves, but they lack the fine control of those alternatives, in throttling applications.
The ball valve’s ease of operation, repair, and versatility lend it to extensive industrial use, supporting pressures up to 1,000 bar (100 MPa; 15,000 psi) and temperatures up to 752 °F (400 °C), depending on design and materials used. Sizes typically range from 0.2 to 48 inches (5.1 to 1,219.2 mm). Valve bodies are made of metal, plastic, or metal with a ceramic; floating balls are often chrome plated for durability.
How Does Ball Valve Work?
A ball valve is a shut-off valve that allows or obstructs the flow of liquids and gases in a piping system by rotating the ball having a bore inside the valve for 90°. The ball is mounted against two seats and has a stem that connects it to the operating and control mechanism that rotates the ball.
When the cross-section of the bore is perpendicular to the area of the flow, the fluid is not permitted to pass through the valve. Otherwise, the fluid flows out from the valve.
Ball valves are one of the quarter-turn valves along with plug valves and butterfly valves. They are widely used in piping systems. They can be operated manually or by using an actuator. The simplest operation of a ball valve is through the use of a wrench or a lever manually turned by an operator.
A torque is applied to rotate the lever arm by 90° either clockwise or counterclockwise to open or close the valve. If the lever arm is parallel to the pipe, it indicates that the valve is open. On the other hand, if the lever arm is perpendicular to the pipe, it indicates that the valve is closed.
The operation of a ball valve is only limited to shut-off and on. It is not advisable to utilize ball valves for throttling as they lack fine controls for flow rate regulation.
Parts of a Ball Valve
Ball valves are constructed with several crucial components:
- Valve Body. This is the main part of the valve and contains all of the components for on/off control.
- Rotary Ball. The ball is designed with a center bore (hole) that the media flows through. The direction of the ball is controlled by turning the stem.
- Stem. This connects the ball to the external control mechanism. For example, in a manual ball valve the stem is connected to a handle or lever.
- Seats. These are discs that lie in between the body and the ball. Seats provide a seal between the two and also support the ball.
- Power Source. The stem of the ball valve is rotated using manual or actuated power sources. Manual actuation includes levers and handles that are controlled by an operator. Automated power sources like electric, pneumatic and hydraulic actuation are also available.
- Packing. This is a seal around the stem that prevents the media from escaping.
- Bonnet. The bonnet is the part of the body that contains the stem and packing.
Types of Ball Valve
There are four general body styles of ball valves: single body, split body, top entry, and welded. There are four general types of ball valves: full port, standard port, reduced port, and v port.
- A full port ball valve has an oversized ball so that the hole in the ball is the same size as the pipeline resulting in lower friction loss. Flow is unrestricted, but the valve is larger.
- A standard port ball valve is usually less expensive, but has a smaller ball and a correspondingly smaller port. Flow through this valve is one pipe size smaller than the valve’s pipe size resulting in slightly restricted flow. In reduced port ball valves, flow through the valve is one pipe sizes smaller than the valve’s pipe size resulting in restricted flow.
- A v port ball valve (Venturi port) has either a ‘v’ shaped ball or a ‘v’ shaped seat. This allows the orifice to be opened and closed in a more controlled manner with a closer to linear flow characteristic. When the valve is in the closed position and opening is commenced the small end of the ‘v’ is opened first allowing stable flow control during this stage. This type of design requires a generally more robust construction due to higher velocities of the fluids, which would quickly damage a standard valve.
- A trunnion ball valve has a mechanical means of anchoring the ball at the top and the bottom, this design is usually applied on larger and higher-pressure valves (say 4 inch and above 600 psi and above)
- Manually operated ball valves can be closed quickly and thus there is a danger of water hammer. Some ball valves are equipped with an actuator that may be pneumatically or motor (electric) operated. These valves can be used either for on/off or flow control. A pneumatic flow control valve is also equipped with a positioner which transforms the control signal into actuator position and valve opening accordingly.
Ball Valve Types Based on Valve Housing:
The ball valve divides into the following commonly used types.
1. Single Body or One-Piece Ball Valve:
Single body or one-piece valve includes in the famous types of the ball valve. It has a solid cast body to reduce the risk of leakage. It is the cheapest type of ball valve. These types of ball valves cannot open for maintenance or cleaning. Single body valves are typically used in less demanding functions. Single body valves often have smaller openings, are relatively cheap, and are generally disposable.
2. Two-Piece Ball Valve:
The two-piece valve consists of two parts; one part has an end joint and body, the second is attached to the 1st part, the trim is attached in place, and includes the second end joint. This valve can disassemble for inspection, maintenance, and cleaning.
To separate the two parts, it must be completely detached from the pipeline. The inside diameter of a two-piece ball valve is usually slightly condensed and can be used or repaired once.
3. Three Piece Body Valve:
These types of ball valves have three parts: a body and two end caps. Usually, all three parts are bolted together. The three-piece design makes it easy to remove the valve‘s core, including the seat, stem, and ball, from the pipe.
This allows you to effectively remove debris, replace seats and seals, and minor polish scratches on the ball without removing the tubing from the valve body. The advantage of this personification is that the valve can repair without eliminating the valve from the pipe. Compared to other types of ball valves, these have a high price.
4. Top Entry Valve:
It is a type of ball valve that assembles the ball from its side part of the top section. The body of this valve allows the seat and ball to be repaired without disassembling the valve. This is the first choice for a larger valve body. It is not necessary to remove the valve from the pipeline.
It is usually made of cast metal. Since it is made by casting, some additional NDT testing is required to ensure that the casting process is free from defects. The benefit of these types of ball valves is that their design allows for minimal threaded connections and minimizes leakage paths.
5. Side Entry Ball Valves:
It is a type of ball valve where the ball assembles from the side part. Mostly, it assembles in 2 or 3 parts of the body. Each body part assembles with screws/studs, such as to connect two flanges’ pieces. Side entry ball valves are generally made of forged metal.
Assemble each body part after forging. This design minimizes defects caused by the casting valve. These valves have an easy assembly. Its trim also has a comfortable alignment. These types of ball valves have quick delivery times while casting products requires additional testing.
6. Welded Body Ball Valves:
It is a fully welded valve and does not pass-through leakage paths by bolt connections. It cannot be repaired on-site. These types of ball valves use are used in buried or underground applications where maintenance is not desirable, like in subsea and gas transport purposes.
All body welding processes are suitable for construction materials and are identified and carried out according to the relevant criteria. The non-destructive testing (NDTS) must also be accomplished on the perimeter welded joints of the body.
Advantages of ball valves
- Efficiency: Ball valves don’t need any lubrication, and offer a bubble-tight seal with low torque.
- Affordability: They can often be purchased at a considerably lower cost than comparable products for the same job.
- Durability: They offer a long service life and, when used under the right conditions, will provide many years of reliable use. Ball valves are less prone to damage than other kinds of valves, and the plastic variety aren’t susceptible to corrosion.
- Easy to use: Ball valves are relatively quick and easy to install, and plastic ball valves are light and easy to handle.
- Versatile: They’re appropriate for a wide range of industrial applications where it’s necessary to regulate the flow of liquids or gases.
- Strong: Ball valves can maintain and regulate high pressure, high volume and a high flow of temperature.
- Simple to repair: Easily access the seats when a valve requires fixing.
Disadvantages of ball valves
The main disadvantages of these valves are as follows:
- Poor throttling characteristics: In a throttling position, the partially exposed seat may be prone to erosion as a result of high velocity flows. They’re therefore not recommended for sustained throttling applications.
- Wear and tear: When used to regulate the wrong types of fluids, such as slurries, ball valves can stick in position and become jammed due to suspended particles being trapped. This can cause the valve to wear, or to become damaged or stuck.
