Globe or rotary?
| Globe (linear) | Rotary | |
|---|---|---|
| Examples | Top-guided single seat, cage-guided, angle valves | Eccentric plug, segmented ball, butterfly |
| Strengths | Precise control, wide choice of special trims for high pressure drop | High capacity, compact, economical in larger sizes |
| Typical use | Steam, feedwater, high-ΔP and severe service | Slurries, viscous fluids, large flows, lower ΔP |
Sizing with Cv
Valve sizing calculates the required flow coefficient (Cv or Kv) from the minimum, normal and maximum flow and the pressure conditions, following standards such as IEC 60534 / ISA-75. Aim for normal operation in the middle of the valve's travel — an oversized valve controls poorly near its seat.
Flow characteristic
Equal percentage characteristics suit most pressure, flow and temperature loops where the available pressure drop changes with flow; linear characteristics suit loops where the valve takes most of the system pressure drop, such as many level loops.
Cavitation, flashing and noise
When liquid pressure falls below vapour pressure inside the valve, bubbles form and collapse (cavitation), damaging trim and body. If outlet pressure stays below vapour pressure, the flow flashes. Gas valves at high pressure drop create noise. Multi-stage trims — for example KOSO's VeCTor trims and cage-guided designs — reduce velocity step by step to control these effects.
Shut-off class
Leakage classes (for example Class IV, V or VI to IEC 60534-4 / ANSI/FCI 70-2) define allowable seat leakage. Specify only what the process needs: tighter classes cost more and may need special seats.
Actuators and positioners
Pneumatic diaphragm or piston actuators are common, with fail-open or fail-closed action chosen for safety. A smart positioner such as KOSO's KGP series compares the control signal with valve position and corrects it, and provides diagnostics over HART.
Information we need to size a valve
- Fluid, its state and properties
- Minimum, normal and maximum flow with corresponding inlet and outlet pressures and temperature
- Line size, pressure class and end connections
- Fail action, shut-off class and control signal
Frequently asked questions
Why is my control valve hunting?
Common causes are oversizing, a mismatched characteristic, stiction or a poorly tuned positioner or loop. A valve diagnostic check helps find the cause.
Browse KOSO products at EECG
EECG is an authorised channel partner for KOSO in Central India, with supply, installation and service support from our Raipur team.
KOSO range → Search our catalogue for “control valve” →Need help selecting the right product for your process conditions? Share your duty and our engineers will recommend a model and send a quotation.
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