Ball Valve Introduction: Structural Features, Fail|electric

Ball Valve Introduction: Structural Features, Failure Analysis, Applications

Sep.19.2024

Ball valves, which emerged in the 1950s, have rapidly developed into a major category of valves over a few decades. The earliest ball valves evolved from plug valves, using a ball instead of a plug to control fluid flow. The flow passage area within the valve matches the pipeline diameter, allowing fluid to pass straight through with minimal pressure drop. Operation from fully open to fully closed requires only a 90° turn of the valve stem. The valve assembly consists of a few different components, making it easy to maintain and repair. Ball valves are very suitable for transporting fluids like liquids and gases. However, as the seats are typically made from rubber, nylon, or PTFE, the operating temperature is generally limited to below 200°C. For slurries, solids, or high-temperature media, metal seats must be used. Today, ball valves are widely applied in various fields such as petrochemicals.

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Ⅰ. Ball Valve Classification
1. By Structure: Classified into Floating and Trunnion Ball Valves based on the support mechanism.
2. By Mounting: Divided into Top-Entry, Side-Entry (One-Piece, Two-Piece, Three-Piece), and Angled Ball Valves based on the ball installation method.
3. By Ball Structure: Includes Integral Ball, Segmented Ball, and V-Port Ball (Arched Segment Ball, Elliptical Segment Ball) Ball Valves.
4. By Flow Passage: Classified into Two-Way, Three-Way, and Four-Way Ball Valves.
5. By Seat Material: Divided into Soft-Seal and Hard-Seal Ball Valves based on the material of the internal parts (mainly the seat).
6. By Actuation: Includes Manual, Pneumatic, Electric, and Hydraulic Ball Valves.
7. By Application: Categorized into Vacuum Ball Valves, Cryogenic Ball Valves, High-Temperature Ball Valves, Insulated Jacket Ball Valves, and Corrosion-Resistant Lined Ball Valves.

Ball valves can be classified in many ways. The most common categories are four: Floating Soft-Seal Ball Valves, Floating Hard-Seal Ball Valves, Trunnion Soft-Seal Ball Valves, and Trunnion Hard-Seal Ball Valves, as illustrated.

Fleyenda Flow Floating Soft-Seal Ball Valve

Fleyenda Flow Floating Hard-Seal Ball Valve

Fleyenda Flow Fixed Soft-Seal Ball Valve

Fleyenda Flow Fixed Hard-Seal Ball Valve

Ⅱ. Characteristics of Ball Valves

Compared to other valve types, ball valves have several advantages. Firstly, they have a high flow capacity. Ball valves are available with reduced and full bore configurations, and regardless of the design, they generally have a low flow resistance coefficient. Secondly, they offer quick and easy operation. Typically, a 90°rotation of the valve stem is sufficient to fully open or close the valve, enabling rapid actuation. Additionally, ball valves are equipped with an anti-blowout stem design to ensure safer usage and maintenance.

Main Characteristics of Soft-Seal Ball Valves
1. Soft-seal ball valves typically feature a high-platform direct-mount design with an adjustable concealed packing gland. The packing can be adjusted without disassembling the cylinder or any other components.
2. Good Sealing: Currently, most soft-seal ball valve seats are made from non-metallic elastic materials, providing excellent shut-off capabilities and ensuring zero leakage.
3. Fire Protection Structure: According to AP1607 design requirements, soft-seal ball valves feature a fire-safe structure: two seals—one soft seat and one metal back-up seat. Even in the event of a fire, the valve maintains support and sealing, preventing leakage.
4. Anti-Static Device: The valve stem is equipped with two conductive small steel balls. These balls maintain constant contact with the valve body and ball under force, allowing static electricity generated by fluid collisions to be discharged during operation.
5. Self-Relieving Seat Design: This design prevents residual liquid or gas media inside the valve cavity from causing explosive pressure increases due to temperature rise when the valve is fully closed or fully open.
6. Long Lifespan: Non-metallic seats, such as PTFE, provide good self-lubrication, resulting in low friction and wear against the ball. Improved ball manufacturing processes reduce surface roughness, enhancing the valve’s service life.

Main Characteristics of Hard-Seal Ball Valves
1. Hard-seal ball valves use high-precision machined balls and seats. Depending on the application, the ball and seat surfaces are hard-faced with materials like cobalt-based alloy, nickel-based alloy, or coated with tungsten carbide, providing excellent wear resistance.
2. Sealing Performance: A unique grinding process ensures that the ball and seat surfaces achieve high roundness and smoothness, resulting in bubble-tight sealing and potentially zero leakage.
3. Elastic Sealing Structure: Prevents the valve from seizing due to thermal expansion at high temperatures, ensuring flexible operation even in high-temperature conditions.
4. Applicability: Suitable for fluids containing solid particles or slurries under different temperatures and pressures.

Ⅲ. Design and calculation of ball valves
1) When designing a ball valve, you must first confirm the ball valve diameter d: the ball channel diameter is divided into two types: non-reduced and reduced diameter:

Non-reduced diameter: d is equal to the valve body channel diameter specified in the relevant standards
Reduced diameter: generally d=0.78 the valve body channel diameter specified in the relevant standards. At this time, its transition section is best designed as a cone angle transition to ensure that the flow resistance does not increase.

2) After determining the diameter, you need to determine the ball radius. Generally, R= (0.75~0.95) d is used. For small diameters, the calculation takes a relatively large value for R, and vice versa. In order to ensure that the ball surface can completely cover the valve seat sealing surface, after selecting the ball diameter, it must be checked according to the following formula: D_min=√D₁²+ √d²

D_min: minimum calculated diameter of the ball
D₁: outer diameter of the valve seat contact surface
d: ball channel hole diameter
D: actual diameter of the ball

3) Determination of valve body wall thickness (we generally follow ASME standards) Wall thickness calculation formula: SB=S'B+C

SB: actual wall thickness
S'B: calculated thickness
C: corrosion margin

When determining the calculated thickness S'B, refer to the actual pressure, temperature conditions and material properties. Usually, the ASME B16.34 standard provides a specific wall thickness calculation method.

4) Calculation formula of the relative pressure between the ball and the valve seat: q_MF<q<[q]

q_MF: required relative pressure of the sealing surface
q: calculated relative pressure of the sealing surface
[q]: allowable relative pressure of the sealing surface

5) Calculation of the rotation shortening of the ball valve: M=M_m+M_t+ M_u+ M_o

M: total torque
M_m: friction torque between the valve seat seal and the ball
M_t: friction torque between the valve stem and the packing
M_u: friction torque between the valve stem shoulder and the thrust washer
M_o: friction torque between the valve stem and the O-ring.

6) Valve stem strength calculation:
Torsion stress at the connection between valve stem and ball τ_N₁= M/w₁ ≤ [τ]
Torsion stress at the connection between valve stem and actuator τ_N2= M/w₂≤ [τ]

M: total torque
w₁: torsion coefficient of valve stem section at the connection with ball
w₂: torsion coefficient of valve stem section at the connection with actuator
[τ] : allowable torsion stress of material.

Ⅳ. Leakage Analysis of Ball Valves
Ball valve leakage can be categorized into external and internal leakage. External leakage often results in wastage of raw materials and energy, environmental pollution, and potential hazards such as fire, explosions, or poisoning, leading to significant economic losses.

External Leakage Causes:
1. Valve Body: Commonly caused by casting defects such as pores or sand holes, leading to medium leakage. Usually detected through hydraulic testing.
2. Connections: Leakage at valve body, side body connections, or valve body to pipeline flange connections. Typically caused by issues like improper gasket type, material, or size, poor flange sealing surface quality, or excessive external loads on connection bolts.
3. Valve Stem: Often due to improper design or material selection, causing the valve stem to seize at a specific position, preventing proper closure and leading to significant leakage.
4. Packing Gland: Caused by loose packing gland, inadequate sealing, improper packing type or quality, or aging or wear of the packing.

Internal Leakage Causes:
1. Design and Manufacturing: Issues causing improper sealing and medium leakage, typically through seepage or small continuous discharge.
2. Damage During Handling: Ball or seat sealing surface damage during manufacturing, transport, inspection, installation, or use, leading to leakage.
3. Solid Particles in Medium: Solid impurities in the medium causing improper valve closure and medium leakage, ranging from small seepage to large flow rates.

Applications of Ball Valves
Due to their numerous advantages, ball valves are used widely. Recommended for systems requiring two-position adjustment, strict sealing, slurry, wear resistance, full bore flow paths, quick operation, high-pressure shutoff (large differential pressure), low noise, minimal vaporization and leakage, low operating torque, and low fluid resistance.

Ⅴ. How to Choose the Right Ball Valve for Various Applications:
- City Gas/Natural Gas Pipelines: Flanged or threaded floating ball valves.
- Oxygen Pipelines in Metallurgy: Strictly degreased ball valves.
- Food Processing Lines: Polished sanitary-grade ball valves.
- Main Pipelines in Oil and Gas Transmission: Full-bore welded ball valves buried underground.
- V-Port Control: Ball valves with V-shaped openings for some regulation performance.
- Petrochemical, Refining, and Power Generation: Soft-seal ball valves for systems operating below 200°C and hard-seal ball valves for systems above 200°C.

In conclusion, ball valves are extensively used and their global supply is increasing annually. The development trend includes high temperature, high pressure, large diameter, high sealing performance, long life, excellent regulation, and multifunctionality. Due to their corrosion resistance, lightweight, and cost-effectiveness, they have partially replaced gate valves, globe valves, and control valves. With advancements in ball valve technology, their use in industries such as pulp and paper, natural gas transmission, refining, and nuclear power is expected to expand significantly in the foreseeable future.

Fleyenda Ball Valve

Fleyenda focuses on designing, manufacturing, and delivering top-tier products while providing exceptional customer service. Our product range includes various valves, such as manual valves, electric valves, pneumatic valves and flow control valves accessories. These valves are designed to meet the needs of various industries, including petrochemicals and chemicals, oil and gas, water and wastewater, pharmaceuticals and biotechnology, and new energy sectors.

Feel free to contact us for valve details and the latest valve quotations. Fleyenda’s professional team is dedicated to helping you find the perfect solutions for your applications.