Instrument Selection | Control Valve Selection Principles Every Instrumentation Professional Should Know

The selection of control valves should be based on a comprehensive consideration of factors such as intended use, operating conditions, fluid properties, piping material class, regulation performance, control system requirements, fire safety requirements, environmental protection requirements, energy efficiency requirements, reliability, and cost-effectiveness. Control valves typically include globe valves, plug valves, butterfly valves, eccentric rotary valves, diaphragm valves, and angle valves, while on-off valves primarily use ball valves, gate valves, plug valves, and butterfly valves.

For control valves with a nominal diameter of DN200 (8 inches) or smaller, globe control valves are generally recommended under standard operating conditions.

For control valves with a nominal diameter of DN250 (10 inches) or larger, eccentric rotary valves or butterfly control valves are generally recommended under standard operating conditions.

For applications involving media containing solid particles or with high viscosity, eccentric rotary valves or V-port ball control valves are recommended.

For high-noise applications caused by high differential pressure, high flow velocity, flashing, or cavitation, low-noise control valves are recommended.

For applications with special process requirements, severe operating conditions, or unique media, specialized control valves such as angle valves, three-way valves, diaphragm valves, plug valves, bellows-sealed valves, micro-flow valves, and cryogenic service valves may be used.

For compressor anti-surge control applications, anti-surge control valves must be used.

For applications such as desuperheating and pressure reduction in steam networks or bypass control for steam turbines, steam desuperheaters and pressure reducing stations should be used.

When the plant has a reliable instrument air system, pneumatic control valves are the preferred choice. When there is no instrument air system but a reliable power supply system (classified as a first-grade load) is available, electric control valves are recommended. When specific process or unit requirements exist, electro-hydraulic control valves may also be selected.

Unless otherwise specified by process requirements, the allowable leakage class for control valves is typically Class IV as defined by the GB/T 4213 or ANSI/FCI 70-2 standard. When the process requires tight shutoff (TSO) or the valve is part of an emergency shutdown interlock, the allowable leakage class should be Class V or higher as per GB/T 4213 or ANSI/FCI 70-2.

When fire safety requirements are specified for control valves, fire-safe control valves compliant with API 607 or API 6FA standards must be selected.

The pressure rating, valve body material, and piping connection type and class of the control valve shall conform to the specifications of the piping system where it is installed. When specified according to NACE requirements, the valve body and trim materials must comply with NACE MR0103 or MR0175 standards.

The control valve size should be calculated based on process parameters to ensure optimal control performance.

Valve installation brackets, bearings, keys, pins, fasteners, and other accessories should be made of steel materials. Asbestos or asbestos-containing materials shall not be used for valve packing and gaskets.