2-Way Ball Valves Types and Uses
What is a Ball Valve ?
A ball valve is an on-off or a shut-off valve. 2-way ball valves control the flow of the liquid or gas medium with a rotary ball, stem, and bore. A ball valve is also a quarter-turn valve and can be used where quick and frequent operation is essential.
Conventional ball valves have relatively poor throttling characteristics because the exposed seat can rapidly erode in a partially open or closed position.
1. What are the advantages of 2-way ball valves?
They provide reliable sealing capabilities. The ball is highly polished to provide tight shutoff, reducing the likelihood of leaks even if the system is not used after a long time.
They are made of highly durable and long-lasting materials like carbon steel or stainless steel. Stainless steel 2-way ball valves are very resistant and used for harsh environments with high temperatures and chemicals.
They offer faster shut-off due to their quarter-turn valve. It is called a quarter-turn valve because the handle only needs a quarter turn (90° turn) to allow or block the flow of the medium, which is extremely important during emergencies.
It is easy to spot the open or closed state of the valve as you can visually detect the position of the handle.
2. When should I use 2-way ball valves?
The following checklist can be used to see if a 2-way ball valve is suitable for use.
- Require more than 2 ports: A ball valve can have 2 to 4 ports (2-way, 3-way or 4-way ball valves).
- Lower flow capacity: 2-way ball valves are usually in smaller diameters, with lower flow capacity.
- Faster opening or closing speed: It only requires a quarter turn (90° turn) to allow or block the flow of the medium.
- Need a tight seal and have complete shut-off: 2-way ball valves provide reliable sealing capabilities.
- Used for low-pressure applications: This is to prevent hydraulic shock (water hammer).
- Used for non-abrasive services: Ball valves are generally soft seated which makes them unsuitable for abrasive services. The soft seals can be damaged by solid particles or trapped in body cavities.
3. What are the different housing assemblies for the 2-way ball valve?
There are 3 commonly used designs - 1-piece, 2-piece, or 3-piece housings- which affect how the valve is assembled and maintained.
- 1-piece valves cannot be disassembled for maintenance. This is the cheapest variant and is often used for low demanding applications.
- 2-piece valves can be disassembled for maintenance and inspection. The valve must be completely removed from the pipeline to separate the two parts.
- 3-piece valves are the most expensive variant as the valve can be repaired without completely removing the entire valve from the pipeline.
4. What are the different ball types?
Depending on how the ball is supported, there is either the floating ball design or trunnion ball design.
In a floating ball design, the ball is held between the seats. It is used for small bore valves (up to 6") in class 150 and class 300 ratings.
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 designs in sizes 1 1/2" and above.
5. What are the different port patterns?
Ball valves are available in the following port patterns:
- Reduced Port
- Venturi Port
- Full Port
For 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 subjected to pigging operations and require the bore of the ball valve to match the internal diameter of the pipeline.
They are also specified in hot-tapping applications and where pressure drop across the valve becomes very critical.
6. What are the seat designs available for ball valves?
Soft seat design:
Ball valves are usually provided with soft seats such as PTFE, filled PTFE, nylon, Buna-N, and Neoprene. These soft seats limit the maximum working temperature and make the valve unsuitable for abrasive service.
When the valves are provided with soft seats, the anti-static design ensures electrical continuity between the ball, stem, and body of the valve.
Metal to metal design:
For abrasive service applications or high integrity applications such as very high pressure, temperatures above 392°F, or if solid particles are present in the fluid, metal to metal seated ball valves can be used. They incorporate tungsten carbide coating.
For high-temperature services, 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.
7. How to use a 2-way ball valve effectively and safely?
2-way ball valves are best used for low-pressure applications, to prevent hydraulic shock (water hammer). 2-way ball valves offer quicker shut-off due to their quarter-turn valve. This abrupt shutoff of the medium might cause a pressure surge, generating a noise like the pipes are being struck with a hammer (water hammer). This powerful water hammer can rupture the system and cause a leak. To reduce the effects of water hammer, several safety features like expansion tanks, accumulators and blow-off valves can be installed.
If the valves are used on high-pressure gas applications, use explosive decompression O-rings. When normal elastomeric O-rings are used, there is the possibility of gas being absorbed into the molecular structure. If the valve is subjected 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.
If a fire-safe design is required, the valve will be labelled as "FIRE-SAFE" in accordance with one of the following specifications: ISO 10497, BS 6755-2, API 607, or API 6FA.
2-way ball valves also have a chance for failure. The valve either would not seal fully due to a damaged seal or the valve would not move as debris is blocking the valve. It is important to perform frequent checks to ensure that the seal isn’t damaged and clear any debris that entered the valve.
8. What do I look out for when purchasing a ball valve?
When purchasing a 2-way ball valve, do look out for the following:
- Valve size
- Pressure class
- Ball type: floating ball or trunnion mounted design
- Pattern: standard pattern or short pattern
- Bore: full bore or reduced bore
- Ends: flanged ends, socket-weld, threaded or butt-weld ends
- Anti-static device
- Details of Operator: lever, gear, or actuator (electric, pneumatic or hydraulic-operated)
- Above ground or buried valve with an extended stem (specify the depth of burial and the dimension of stem extension)
- Body, seat rings, trim, trunnion, seals, bolts, nuts, gaskets, and packing material
- Certification requirements
If required, do look out for the following:
- Lifting eyes or lugs: usually specified for valves weighing over 250kg
- Seating (if not a soft seated valve e.g. metal seated design)
- Orientation of valve (if the valve is not installed with the stem vertically up)
- Valve support (if required by stress analysis): custom-designed, usually not valve supports supplied as part of standard design
- Face to face dimension (if non-standard)
- Locking device (if required): to retain the valve in locked open or lock closed position
- Drain connection (if required)
- Sealant injection connection (if required)
- Hot-tap operation (if required)
- Fire-safe test (if required)
- Integral bypass connection (if required)
- Painting specification (applicable to the project)
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