Globe Valve Flow Characteristics and Selection

Globe valves offer excellent flow control characteristics and reliable shutoff in a wide range of process applications. Understanding their flow characteristics, pressure drop behavior, and application limitations is essential for proper selection and sizing.

Flow Characteristic Curves

• Linear: flow proportional to valve opening, used in flow control loops

• Equal percentage: each increment of opening produces equal % flow increase

• Quick opening: large flow increase at small openings, used for on-off service

• Characteristic selection matches valve gain to process dynamics

• Installed characteristic differs from inherent due to system pressure drop

Plug and Seat Configurations

The relationship between plug shape and seat geometry determines the flow characteristic. Parabolic plugs produce equal percentage characteristics. V-port plugs provide linear or modified equal percentage characteristics with improved rangeability. Contoured plugs can be designed for specific application requirements. For metal-seated globe valves, the plug and seat are lapped to achieve the required shutoff class.

Pressure Drop and Valve Sizing

• Cv coefficient relates flow to pressure drop for liquid service

• Fp (liquid pressure recovery factor) accounts for vena contracta effects

• Cavitation analysis required when pressure drop exceeds fluid vapor pressure

• Anti-cavitation trim uses staged pressure reduction to prevent damage

• Maximum allowable pressure drop limited by choked flow conditions

Applications by Fluid Type

Globe valves excel in liquid service, steam throttling, and applications requiring frequent cycling. They are preferred for flow control where precise, stable throttling is required. Globe valves are not recommended for high-viscosity fluids, slurries, or services where minimal pressure drop is required, as the tortuous flow path creates significantly higher pressure drop than gate or ball valves.

Angle Valve Configuration

• 90° body configuration for end-of-line or pipe-turn installations

• Reduces piping complexity and eliminates elbow pressure drop

• Self-draining configuration for condensate-prone services

• Reduced erosion in two-phase flow compared to straight-through design

• Available in all pressure classes and materials of globe valve family