What is Ball valve? Parts, Advantage, Industry Codes and Standards?

Ball Valve - Introduction    

    A ball valve is an on-off or a shut-off valve.  A ball valve is a quarter-turn valve and is used where quick and frequent operation is essential.

Conventional ball valves have relatively poor throttling characteristics.  In a partially open or closed position, the exposed seat can rapidly erode.  Ball valves are generally soft seated which makes them unsuitable for abrasive service.  The soft seals can be damaged by solid particles or trapped in body cavities.

Ball valve 

most applications reduced port ball valves are specified as they are less expensive than the full port or full bore valves. Full bore valves are used in pipelines which are often subject to pigging operations and require the bore of the ball valve to match the internal diameter of the pipeline. Full bore valves are also specified in hot-tapping applications and where pressure drop across the valve becomes very critical.

ing and Trunnion Mounted Design: Depending on how the ball is supported, ball valves fall under the following categories :

o    Floating ball design

In a floating ball design, the ball is held between the seats. Floating ball design is used for small bore valves (up to 6") in class 150 and class 300 ratings.

o    Trunnion ball design

 In a trunnion ball design, the ball is supported below the ball. Class 150 and 300 rated valves 8" and above are normally specified with trunnion mounted ball design. Class 600 and above rated valves normally have trunnion mounted design in sizes 1 1/2" and above.

Ball Valve Seat Design: Ball valves are usually provided with soft seats such as PTFE, filled PTFE, Nylon, Buna-N, Neoprene which limits the maximum working temperature and makes the valve unsuitable for abrasive service. For abrasive service applications or high integrity applications metal to metal seated ball valves can be used as described below.

Metal to Metal Seat: For applications where elastomeric seats would be inappropriate, such as very high pressure, temperatures above 392°F, or where solid particles are present in the fluid, valves are provided with metal/metal seating, incorporating tungsten carbide coating. For high-temperature service, the valves are normally fitted with extension bonnets, to ensure that the operator is located in the ambient temperature zone. Metal seated ball valves are normally used, whenever a high safety level is required, as in the HIPPS application. Seat leakage test is carried out in accordance with BS 6755 part I, rate B.

Ball Valve Fire Safe Design: If a fire-safe design is required, the valve shall be qualified as "FIRE-SAFE" in accordance with one of the following specification, ISO 10497, BS 6755-2, API 607 or API 6FA.

Anti-static Design: When valves are provided with soft seats, their design shall ensure electric continuity between the ball and the body, by means of an anti-static device. The anti-static design ensures electrical continuity between the ball, stem, and body of the valve.

Explosive decompression

Wherever valves are used on high-pressure gas applications, there is the possibility of gas being absorbed into the molecular structure of elastomeric O-rings. If the valve is then subject to sudden decompression, the gas will expand rapidly and may destroy the O-ring. To eliminate this possibility, special O-rings or lip seals, suitable for such service conditions, are available.

Parts of a Ball Valve

Figure below shows various parts of a typical lever operated ball valve.

Parts of the Ball valve

Advantages of Ball Valve 

• Ball valves are rotary motion valves and require only a quarter of a turn (90-degree rotation) to open or close the valve. This makes the ball valves quick-acting and hence are recommended for emergency shutdown applications.
•  Since ball valves are available in soft seat designs it is possible to get a bubble-tight shutoff with ball valves with clean fluid service.
• Ball valves require a smaller space envelope when compared to gate valves
• Ball valves do not require lubrication.

Disadvantages of Ball Valves

• In general ball, valves have relatively poor throttling characteristics. In a throttling position, the ball valve seat gets partially exposed and rapidly erodes due to the impingement of high-velocity flow.
• Debris or solid particles in piping service can settle-out and become trapped in the cavities below the ball and surrounding the stem or trunnion areas.

 Industry Codes and Standards

• API 6D - Specification for Pipeline Ball valves  
• API 598 - Valve Inspection and Testing
• API 6FA - Fire Test for Valves
• BS 5351 - Specifications for steel ball valves for the petroleum, petrochemical and allied industries.
• BS 6755 Pt. 1 - Specification for production pressure testing requirements.
• BS 6755 Pt. 2 - Specification for fire type-testing requirements.
• MSS SP 72 - Ball Valves with Flanged or Butt Welded Ends for General Service
• MSS SP 61 - Pressure testing of steel valves
•  MSS SP 25 - Standard marking system for valves, fittings, flanges & unions
• MSS SP 45 - Bypass and drain connections

Pipeline ball valves are specified to API 6D. Pipeline ball valves have special features which are described in the link below. Pipeline ball valves.

Ball valves used in hazardous areas where they could be subjected to fire shall be of a fire tested design

Operators for Ball Valves

Most operators use the following guidelines to select the type of operators for Ball valves. When the effort to operate the lever exceeds 350 N geared operators are provided.

Operator	Size	Rating
Handwheel	6-inch and below	Class 150 and 300
Handwheel	4-inch and below	Class 600 and 900
Handwheel	3-inch and below	Class 1500 and 2500
Gear Operator	8-inch and above	Class 150 and 300
Gear Operator	6-inch and above	Class 600 and 900
Gear Operator	4-inch and above	Class 1500 and 2500

When the lever the position is along the axis of the valve, the valve is in an open position. A lever position at a right angle to the axis of the valve indicates that the valve is closed.

Ball Valve Purchase Specification

The following information or parameters should be included for purchasing a ball valve:

1. Valve Size
2. Pressure Class
3. Ball-type - Floating ball or Trunnion mounted design
4. Pattern - specify standard pattern or short pattern 
5. Bore - specify full bore or reduced bore
6. Ends - specify flanged ends, socket-weld, threaded or butt-weld ends (specify matching wall the thickness for welded end valves) 
7. Face to face dimension if non-standard 
8. Drain connection if required
9. Sealant Injection connection if required
10. Locking device if required - to retain the valve is locked open or lock closed position
11. Valve support - if required by stress analysis (this refers to custom-designed support and not the valve supports supplied as part of standard design which is only for transportation purposes)
12.  Anti-Static device
13. Details of Operator - Lever or Gear or Actuator (Electric, Pneumatic or Hydraulic Operated) 
14. Above ground or buried valve with the extended stem (specify the depth of burial and the dimension of stem extension) 
15. Body, Seat Rings, Trim, Trunnion, Seals, Bolts, Nuts, Gaskets and Packing material
16. Seating if not a soft seated valve (e.g. Metal seated design)
17. The orientation of the valve (if the valve is not installed with stem vertically up)
18. Specify if a valve is required for hot-tap operation
19. Certification requirements
20. Fire-safe test if required
21. Painting specification (applicable to the project)
22. Integral bypass connection if required
23. Lifting eyes or lugs (usually specified for valves weighing over 250kg)