310104b Rotary Control Valves 2017 TF (1)

Objectives of Rotary Control Valves

• Application and Construction: Understand the wide uses and structure of rotary control valves.

• Hazards Identification: Recognize potential dangers associated with rotary control valves.

• Servicing Procedures: Learn the procedures involved in maintaining and servicing rotary control valves.

Rotary Control Valves Overview

• Definition: Valves that operate based on the rotation of a valve shaft.

• Common Types:

  • Ball Valves: Utilize a spherical disc to control flow.

  • Rotary Plug Valves: Feature a cylindrical plug that rotates to regulate flow.

  • Butterfly Valves: Employ a thin, rotating disc to control flow.

  • Positioned Disc Valves: Utilize a moveable disc with holes to throttle flow.

Ball Valve Characteristics

• Flow Characteristics: Generally provide equal percentage flow characteristics, showing little flow at low openings and high flow with wide openings.

• Flow Dynamics: Process flows against the face of the ball, causing the ball to be a key regulator in fluid flow control.

Construction and Features of Ball Valves

• Seal Rings: Commonly constructed from Teflon (PTFE), providing:

  • Tight shut-off capabilities.

  • Self-cleaning properties for the ball face.

Control Ball Valves

• Design: Segmented or half-ball design, generally trunnion mounted.

  • Sweep: Performs a 90° rotation to achieve full opening.

  • Flow Capacity: Supports wide flow ranges and high flow capacity.

  • Applications: Effective for general flow applications, including slurry service.

  • Actuator Requirement: Requires relatively powerful actuators due to high friction forces during operation.

Ball Valve Mechanics

• Actuation: Requires a rotary actuator to facilitate 90° rotation.

• Port Shape: The ball may feature a V-shaped port or similar design for achieving specific flow control characteristics.

• Caution: Not recommended for steam service applications.

Different Types of Actuators

• Rotary Actuator Types:

  • Electronic Positioner

  • Pneumatic Positioner

Plug Valve Characteristics

• Structure: Similar to ball valve; features a cylinder-shaped plug.

• Flow Type: Provides straight-through flow, promoting good recovery properties.

• Conditions:

  • Closed State: Forward-flow throttling.

  • Open State: Permits normal fluid passage.

Rotary Stem Eccentric Plug

• Design: Incorporates an eccentric disc (Fisher E-disc) allowing:

  • Rotation through approximately 50°.

  • Tight shut-off and low operating torque for efficiency.

Butterfly Valve Overview

• Design Attributes:

  • Compact and Economic: Ideal for applications requiring high capacity with low pressure loss.

  • Leakage Factors: All-metal designs may leak up to 1% of maximum flow.

• Shut-off Mechanism: Can achieve 100% positive shut-off with elastomer liners.

• Operational Range: Typically rotated 60° for control applications to minimize torque requirements.

• Body Options: Available in wafer or flangeless body styles.

Butterfly Valve Fish Tail Design

• Functionality: Allows for controlled flow with varying throttle angles from closed to open positions (0° to 90°).

Positioned Disc Valves

• Mechanism: Rotates a movable disc with holes to progressively throttle flow.

• Applications: Suitable for high-pressure environments (e.g., oil well flow).

• Material Strength: Utilizes tungsten or carbon discs, capable of withstanding up to 10,000 psi.

Summary of Rotary Valves

1. Rotary Stem Eccentric Plug: Rotates through 50°, enables tight shut-off with low torque.

2. Ball Valve: Requires 90° rotation, exhibits high friction necessitating powerful actuators.

3. Butterfly Valve: Offers economical operation, usually rotates through 60°, provides high capacity, and excellent recovery.

Assignments

• Complete the ILM Self-Test to assess understanding of rotary control valves.