What is Ball valve? Types and functions in detail

A ball valve is one of the most common valves used for commercial as well as residential plumbing applications. The basic function of a ball valve is to on-off the flow using a handle.

Ball valves are known for their long service life, and performance and are often a preferred choice over Gate and globe valves. To explore more about detailed comparison you may want to read our Gate valve vs ball valve post.

A Ball Valve should not be confused with a “Ball Check Valve”, basically a type of Check Valve with a solid ball that is used to prevent undesired backward flow in the line.

Ball valves are also called Quarter turn (1/4) shut-off valves as they require a quarter turn to close the valve enabling operation time shorter.

Did you know?

The biggest ball valve manufactured is 64″ X 48″ which is a hydraulic actuated Control Cage Ball Valves having a flow capacity of 125,500 Cv. And this valve was installed to control the flow of water in a 450 KM (280 miles) pipeline from the Ras Azawr Desalination plant to Riyadh in Saudi Arabia.

Ball valve components

Ball valves structure comprised of five key components:

• Ball
• Stem
• Seat
• Gasket
• Body

BALL

There are different types of balls used in the Ball valve as per the applications. For all three types of ball, the outer surface needs to be crystal smooth for the ball valve operation.

These three types are Solid, Hollow & Cored. Let’s dive into detail to know each of them.

Solid ball
Solid balls are constructed from 100% compact casting or bar stock material with a solid hole having the same diameter throughout.
Due to their construction solid ball usually weigh more than hollow balls & cost more. A solid ball is mostly used for smaller sizes of the ball valves.

Hollow ball
The hollow ball as the name depicts is hollow from the inside that has more room space for the fluid to fill. Basically, it has a cavity that goes from the open hole from the bottom of the ball to the top where the stem of the valve is inserted.

Due to its hollowness, the flowing media changes its velocity and turbulence occurs. This turbulence can create noise and prove to be inefficient. However, the hollow balls may have appreciable advantages in large-size valves.

Cored Ball
Cored Ball is created by having a wall thickness consistency around the whole ball. In this type of arrangement, the balls get cooled more evenly thus decreasing the amount of grinding once it has fully cooled.

Due to this feature, these balls are becoming more popular and are more cost-effective when compared to solid balls.

STEM

The ball valve’s open-close direction is determined by its stem which connects to the ball (solid ball / hollow ball / cored ball).

The stem further connects to the ball disc to the lever, handle, or actuator. The stem controls the on-off ball function which rotates the ball disc in a typical ball valve construction.

SEAT

Seat in ball valves is also known as the seal rings typically where the ball disc rests. It is around a donut-shaped disc that acts as sealing between the ball & body. The seat ring often comes in various materials like PTFE, Peek, and Nylon with PTFE being majorly used.

GASKET

The gasket provides excellent sealing to the stem & bonnet part. Most of the time the issue arises in this area that is why each component of the ball valve must be assembled carefully.

If the components are assembled too loose, leakage will start, and if it is too tight the movement of the stem is restricted.

BODY

The body is the entire framework of the ball valve through which fluid flows. It fits the piping via bolted, threaded, or welded joints which hold the components together.

The body acts as a barrier to the pressure load from the flowing media so that there is no transfer of pressure to the pipes.

Types of Ball valves

Now, this is a very vague question in fact! The definition of the types of ball valves changes mainly in terms of Body parts, ball design, valve assembly, bore size, and so on.

Let’s discuss each one of them along with an example.

Type of Ball valve in terms of main body parts

The main body of the valve is constructed in a single piece, two-piece, and three-piece design. Though the operation of each design is the same the only difference is the assembly which decides the possibilities for maintenance or repair.

What is a single-piece Ball valve?

A single piece or one-piece ball valve has a solid ball inside whereas the valve body is a single piece with a reduced bore mostly. The end connection is either flange end or threaded end in BSP-F / NPT-F as per the fitting requirements.

Manufacturing standards followed are American Petroleum Institute (API) Standards, American Society of Mechanical Engineers (ASME), and British standards (BS).

The single-piece ball valve is the cheapest variant and is generally used for low-demanding applications such as Gas & water applications, General Oil, etc. Maintenance or repair cannot be carried out since these valves cannot be opened once constructed. They are mostly used and throw-away type valves.

What is a two-piece ball valve?

The two-piece ball valve has one body joint and from this joint, the ball is placed inside the valve body.  From the maintenance & service point of view, these valves can be disassembled easily and cleaned.

The valve must be removed from the pipeline in order to separate the two parts before cleaning, servicing, and inspection.

What is a three-piece ball valve?

As the name suggests it consists of three parts viz two pipe connectors (end caps) and the main body. Three-piece ball valves are easily serviceable and one of the most convenient options to choose from.

The big difference in the three-piece ball valve is that it can be easily disassembled without disturbing the two end caps while the two-piece ball valve does not allow this to happen and it’s not at all possible with a single-piece ball valve.

Cost-wise three-piece ball valve tends to be more costly initially but it can save money in the long run in terms of time spent maintaining & repairing vs replacing the valve entirely.

Type of Ball valve in terms of the ball design

There are primarily two types of ball design- Floating ball valve & Trunnion Ball valve.

What is a floating ball valve?

Most of the ball valve uses a floating ball. In the floating ball arrangement, the ball is suspended in media and is supported by two sealing rings. When fluid pressure acts on the ball it then forces the ball into seats giving it a tight seal.

The floating ball has the disadvantage of using in a high-pressure line due to the fact that the high force of the ball against the seat can deform the seat and affect the low pressure sealing characteristics of the valve.   

What is the Trunnion ball valve?

To fulfill the requirements of high operating pressure in the line, the ball used is often the trunnion design. In this design, the ball is supported from top & bottom to significantly reduce the load on seat rings. Trunnion ball valves generally require low torque for operation.

Type of Ball valve in terms of bore size

The hole of the ball varies and can have different profiles such as reduced bore, full bore, or v-shaped.

Reduced bore ball valve

Most of the ball vales have reduced bore that has one pipe size smaller than the nominal valve size. As a result, friction develops in the system over a period of time, but this friction is relatively small in comparison with other valve types.

The reduced bore ball valve is widely used in the system where turbulence & pressure drop is not a concern. They are economical and have less weight and are always in demand.

Full Bore or Full port Ball valve

The full bore ball valve has the same diameter as the connecting pipe. In other terms, full bore is when the I.D. of the pipe is the same as the I.D. of the valve. It has a straight flow path where there is no reduction of the flow.

V-port Ball valve

As the name suggests the ball is “V” shaped and it is used to achieve more precise flow control by rotating the ball. It is also known as a control valve it can control the flow velocities depending on the application.

When the V-port valve is in the closed position and when the opening is performed, the small end of “V” opens first allowing the stable flow control through the valve.

A V-port ball valve is a popular choice among the industries such as food processing, water treatment, pharmaceuticals & chemical, agricultural, and waste processing.

Functions of Ball valve

So far we have learned now that a ball valve is a quarter-turn valve as it controls the flow through a hollow, perforated, and pivoting sphere.

This valve belongs to the same family as of Butterfly valve and plug valve which is also a quarter-turn valve. The main function of the valve is its sphere which is lined up with the associated pipeline.

When the valve is open the fluid move through the bore and when it is closed (turned 90 degrees) the flow of fluid is stopped. By its physical appearance, one can identify easily whether the valve is in open condition or in closed condition.

Due to the lack of throttling operation, it is not suited for those applications where throttling of flow is required.

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