Control Valves — Technical Overview & Selection Guide

Overview

Control valves are automatic final control elements used to regulate the flow, pressure, temperature, level, and other process variables within a piping or process system. They operate by varying the valve opening in response to a control signal from a process control system.

Control valves are selected and sized according to process conditions, flow requirements, pressure drop, fluid characteristics, operating temperature, and required control performance.

Key Features

• Automatic regulation of process flow and operating conditions

• Suitable for flow, pressure, temperature, and level control

• Precise and repeatable flow control

• Suitable for liquid, gas, steam, and multiphase services, subject to design

• Available in linear and rotary control valve configurations

• Wide range of flow characteristics available

• Pneumatic, electric, and hydraulic actuation options

• Available with positioners and control accessories

• Suitable for high-pressure and high-temperature applications

• Available in various body, trim, and seat materials

• Available in ASME Class 150–2500, as applicable

Common Control Valve Types

• Globe Control Valve

• Angle Control Valve

• Cage-Guided Control Valve

• Top-Guided Control Valve

• Rotary Control Valve

• Butterfly Control Valve

• Ball Control Valve

• V-Ball Control Valve

• Eccentric Plug Control Valve

• Three-Way Control Valve

• Split-Body Control Valve

Technical Selection Parameters

Selection should consider:

Materials

Common control valve body materials include:

• Carbon Steel

• Stainless Steel

• Alloy Steel

• Cast Iron, where applicable

• Forged Steel, where applicable

Trim, plug, cage, stem, shaft, and seat materials should be selected based on fluid compatibility, pressure, temperature, erosion, corrosion, velocity, cavitation, flashing, and service requirements.

Trim & Seat

Typical trim and seat configurations may include:

• Stainless Steel Trim

• Alloy Trim

• Hardened Trim

• Anti-Cavitation Trim

• Low-Noise Trim

• Metal-to-Metal Seats

• Soft Seats

• Stellite® or equivalent hard-facing, where specified

Trim selection is particularly important for high-pressure-drop, erosive, corrosive, flashing, cavitating, or high-velocity services.

Flow Characteristics

Control valves may be provided with different inherent flow characteristics, including:

• Linear — Flow capacity changes approximately proportionally with valve travel.

• Equal Percentage — Each increment of valve travel produces a proportional change in flow coefficient.

• Quick Opening — Provides rapid flow increase at low valve travel and is generally used where fast opening is required.

The appropriate characteristic should be selected according to the process dynamics and control-loop requirements.

Actuation

Control valves may be operated using:

• Pneumatic Actuator

• Electric Actuator

• Hydraulic Actuator

• Electro-Hydraulic Actuator, where applicable

Pneumatic actuators are commonly used for industrial process control applications due to their fast response and suitability for automated systems.

Fail-Safe Action

Depending on process safety requirements, control valves may be configured for:

• Fail Open (FO)

• Fail Closed (FC)

• Fail in Place (FIP)

Fail action should be selected based on the safe condition required by the process and control philosophy.

Positioners & Accessories

Control valves may be supplied with:

• Smart Valve Positioner

• Electro-Pneumatic Positioner

• I/P Converter

• Solenoid Valve

• Limit Switches

• Position Transmitter

• Air Filter Regulator

• Volume Booster

• Lock-Up Valve

• Quick Exhaust Valve

• Manual Override, where applicable

Control Valve Sizing

Control valve sizing should be based on the required Cv/Kv, flow rate, pressure drop, fluid properties, and operating conditions.

Important sizing inputs include:

• Minimum Flow

• Normal Flow

• Maximum Flow

• Upstream Pressure

• Downstream Pressure

• Differential Pressure

• Operating Temperature

• Fluid Density / Specific Gravity

• Viscosity

• Molecular Weight for gases

• Vapor Pressure for liquids

• Critical Pressure, where applicable

• Compressibility, where applicable

The valve should be sized to provide stable and controllable operation across the required operating range while avoiding excessive velocity, cavitation, flashing, choking, or unacceptable noise.

Quick Selection Guide

Process Variable: Identify whether the valve will control flow, pressure, temperature, level, or another process variable.

Fluid: Specify liquid, gas, steam, or multiphase service together with relevant fluid properties.

Flow Rate: Provide minimum, normal, and maximum flow conditions.

Pressure: Provide inlet pressure, outlet pressure, and differential pressure for the operating cases.

Temperature: Specify minimum, normal, and maximum operating temperatures and design temperature.

Valve Type: Select globe, angle, ball, butterfly, V-ball, eccentric plug, or another suitable configuration based on service and control requirements.

Cv/Kv: Determine the required flow coefficient based on the applicable process conditions.

Flow Characteristic: Select linear, equal percentage, quick opening, or another characteristic according to the control-loop requirements.

Pressure Drop: Evaluate pressure loss and ensure the selected valve provides adequate control authority.

Cavitation & Flashing: For liquid services, evaluate vapor pressure and pressure recovery to identify potential cavitation or flashing conditions.

Noise: Evaluate aerodynamic or hydrodynamic noise for high-pressure-drop and high-velocity applications.

Actuation: Specify pneumatic, electric, hydraulic, or other actuator requirements.

Fail Action: Define Fail Open, Fail Closed, or Fail in Place based on process safety requirements.

Positioner: Specify conventional or smart positioner and required communication protocol, where applicable.

Shut-Off: Define the required seat leakage class and isolation requirements.

Connection: Specify flanged, butt-weld, threaded, or other applicable end connection.

Testing & Inspection

Depending on project specifications and applicable standards, control valves may undergo:

• Shell/body pressure testing

• Seat leakage testing

• Functional and operational testing

• Control valve performance testing

• Stroking and travel verification

• Positioner calibration

• Fail-action verification

• Dimensional inspection

• PMI (Positive Material Identification)

• MTC verification

• NDE (Non-Destructive Examination)

• Material and coating inspection, where applicable

Applications

Control valves are commonly used in:

• Oil & Gas

• Refineries

• Petrochemical Plants

• Chemical Plants

• Power Plants

• Steam Systems

• Boiler & Feedwater Systems

• Process Piping

• Water Treatment

• Pressure Control Systems

• Flow Control Systems

• Temperature Control Systems

• Level Control Systems

• Gas Processing

• Utilities

• Industrial Plants

Engineering Inputs for RFQ

For technical enquiry and quotation, provide:

Control Valve Type • Size • Pressure Class • Fluid • Flow Direction • Minimum/Normal/Maximum Flow • Inlet Pressure • Outlet Pressure • Differential Pressure • Design Pressure • Operating & Design Temperature • Fluid Properties • Body Material • Trim Material • Seat Type • Required Cv/Kv • Flow Characteristic • End Connection • Actuator Type • Fail Action • Positioner • Accessories • Installation Orientation • Noise/Cavitation Requirements • Shut-Off/Leakage Class • Testing & Inspection Requirements

Manufacturer Brands

1. ZOLOTO — Industrial Valves

Brand: ZOLOTO
Website: www.zolotovalves.com

2. MARCK — Industrial Valves

Brand: MARCK
Manufacturer: Hawa Engineers Ltd.
Website: www.marckvalves.com

3. LEHRY — Industrial Valves and Instrumentation

Brand: LEHRY
Manufacturer: Lehry Instrumentation & Valves Pvt. Ltd.
Website: www.lehryvalves.com

4. UFLOW — Automation and Process Control Valves

Brand: UFLOW
Manufacturer: Uflow Automation India
Website: www.uflowvalve.com

5. V-TORK CONTROLS — Industrial Flow Control Valves

Brand: V-TORK CONTROLS
Website: www.vtorkcontrols.com

6. PENNANT — Steam Traps and Pipeline Accessories

Brand: PENNANT
Manufacturer: Pennant Engineering Pvt. Ltd.
Website: www.pennantcorp.com