PC-09Final control · CV
Control Valves, Actuators & Positioners
The final control element is where the control strategy meets the process. Valve type, trim and characteristic are sized to the flow conditions; the actuator and positioner decide how precisely — and how safely — it moves.
01Scope
What's included
Control and on/off valves, actuators and positioners.
- Globe control valvesLinear throttling valves with characterized trims, including trims for noise and cavitation.
- Rotary control valvesSegmented ball, eccentric plug and high-performance butterfly valves.
- On/off valvesBall and butterfly valves with actuators for isolation, sequencing and shutdown.
- ActuatorsPneumatic diaphragm, piston, rack-and-pinion and scotch-yoke actuators; electric actuators.
- Positioners and accessoriesElectro-pneumatic and digital positioners, I/P converters, limit switch boxes, solenoid valves and filter regulators.
02Compare
Valve and actuation types
Valve style follows the service and the pressure drop; actuation follows the utilities available, the speed required and the fail-safe position.
| Principle | How it works | Suited for | Considerations |
|---|---|---|---|
| Globe valveMedia: LiquidGasSteam | How it worksA plug moves linearly against a seat; the trim shapes the flow characteristic. | Suited forPrecise throttling across wide pressure drops; severe-service trims for noise, cavitation and flashing. | ConsiderationsLarger, heavier and higher in pressure loss than a rotary valve of the same capacity. |
| Segmented (V-port) ballMedia: LiquidGas | How it worksA rotating ball segment with a contoured opening throttles the flow. | Suited forHigh capacity, slurries and fibrous media, wide rangeability. | ConsiderationsAt high pressure drops, more prone to cavitation than a globe valve with anti-cavitation trim. |
| Butterfly (high-performance)Media: LiquidGasSteam | How it worksA disc rotates in the flow path; offset designs improve shut-off and throttling. | Suited forLarge line sizes and low pressure drops — water, air and gas services, and isolation. | ConsiderationsNarrower useful throttling range; dynamic torque typically peaks at about 70–80° open and seating/breakaway torque is highest at closed — size the actuator for both. |
| Pneumatic actuator | How it worksAir pressure on a diaphragm or piston, opposed by springs, moves the valve; spring return gives a defined fail position. | Suited forMost process control valves — fast, reliable and naturally fail-safe. | ConsiderationsNeeds clean, dry instrument air; sized for the valve's thrust or torque with margin. |
| Electric actuator | How it worksA motor and gearbox position the valve; modulating versions accept a 4–20 mA setpoint. | Suited forSites without instrument air, large isolation valves, water and utility networks. | ConsiderationsSlower stroking; fail-safe action needs spring-return or stored-energy options; duty-cycle limits apply. |
| Positioner | How it worksCompares the control signal with the actual valve position and adjusts actuator pressure until they match. | Suited forThrottling valves where precision, speed and diagnostics (friction, air leaks, valve signature) matter. | ConsiderationsAir quality, mounting kit and feedback linkage; some models add partial-stroke testing for shutdown valves. |
General engineering guidance. Limits and performance depend on the specific instrument and variant — confirm them against the manufacturer's datasheet for the selected model.
03Specify
What to specify
The parameters that decide the selection. State each with its unit; where a value is not known yet, say so — it becomes part of the engineering review.
Process fluid and state
Liquid, gas, steam or slurry — it decides valve style, trim and the sizing equations.
Flow conditions
Minimum, normal and maximum flow with inlet pressure, pressure drop and temperature give the Cv / Kv and reveal cavitation or choked flow.
Characteristic and rangeability
Equal-percentage or linear, matched to how the pressure drop changes across the operating range.
Shut-off class
Seat leakage class (e.g. Class IV, V or VI per IEC 60534-4 / FCI 70-2) sets how tightly the valve must close.
Pressure rating and end connections
ASME class or PN rating, flanged or welded ends, and face-to-face dimensions for replacements.
Body and trim materials
Corrosion, erosion and temperature decide body, trim and packing materials.
Fail-safe action
Fail open, fail closed or stay put on loss of air, power or signal — set by the process hazard.
Actuation and utilities
Instrument-air supply pressure or electrical supply, and the stroking speed required.
Control signal and feedback
4–20 mA, HART or fieldbus positioner; limit switches or position transmitter for confirmation.
Noise and area classification
Noise limits may require special trims; hazardous areas need certified positioners, solenoids and switches.
04Integrate
Outputs & communication
Interfaces typically offered in this category, and what each means for the control system. Availability depends on the specific model.
- 4–20 mAAnalog
- Current loop with a live zero: 4 mA is the bottom of the range, so a broken wire (0 mA) is distinguishable from a zero reading. Two-wire (loop-powered) on most transmitters; four-wire with an active output on line-powered instruments such as analyzers — the I/O channel must match. Accepted by practically every PLC and DCS analog input.
- HARTDigital over analog
- A digital signal (Bell 202 FSK, 1200/2200 Hz) superimposed on the 4–20 mA loop — configuration, diagnostics and secondary variables over the existing two wires.
- PROFIBUS PAFieldbus
- Two-wire, bus-powered process fieldbus at 31.25 kbit/s, coupled to PROFIBUS DP — several instruments share one cable, with intrinsically safe variants for hazardous areas.
- FOUNDATION Fieldbus H1Fieldbus
- Two-wire, bus-powered digital fieldbus at 31.25 kbit/s with function blocks in the field devices — used mainly where the DCS architecture is built around it.
- Relay / discreteDiscrete
- Switched contact or transistor output for alarms, interlocks and pump or valve control — it carries a state, not a value.
- Pneumatic 0.2–1.0 barPneumatic
- The classic 3–15 psi pneumatic signal — 20–100 kPa (0.2–1.0 bar) in metric plants — still common on actuators and in existing loops; positioners and I/P converters translate 4–20 mA into actuator pressure.
05Install
Installation practice
- Provide the straight pipe the sizing assumes, and isolation and bypass valves where the process must keep running during valve maintenance.
- Supply clean, dry, oil-free instrument air at the pressure the actuator and positioner need, through a filter regulator.
- Orient actuators and positioners for access, and support heavy actuators so the valve body and piping are not strained.
- After installation, stroke and calibrate the valve with its positioner and verify the fail action together with the control system.
06Products
Control Valves & Actuators products
Status · no models listed
Specific models are not listed on the site.
Our engineers can recommend valves and actuators against your process data. The selection checklist on this page is the information that decides it — send what you have.
How a review runs
CV01Share the process data
Medium, flow and pressure conditions, shut-off, connection and the control signal.
02Engineering review
The valve type, sizing and actuation are checked against the application.
03Valve options
Suitable valves and actuators are proposed with the data needed to confirm the selection.
Next steps
Where to go next
- 01SolutionInstrumentationProcess measurement and final control elements — selected for the process conditions, installed, calibrated and loop-checked.
- 02ResourceWhat an Instrumentation & Automation AMC Should CoverScope, preventive schedules, response planning and records for a useful AMC.
- 03Related categoryPLC, HMI & SCADAControllers, I/O, operator panels and supervisory software.
Engineering enquiry
Sizing a control valve or actuator?
Share the medium, the flow and pressure conditions, the shut-off requirement and the control signal. Our engineers can help select the valve type, the actuator and the positioner for the application.