What Is a Butterfly Control Valve?
In a butterfly valve, flow is controlled by a disk that sits in the pipe and rotates on a shaft. When the disk is parallel to the flow the valve is fully open; when it is perpendicular the valve is closed. General-purpose butterfly valves are mostly used for on-off duty, whereas high-performance butterfly valves use improved disk profiles, eccentric shaft positions and special seal systems that make them suitable for accurate throttling as well as automated on-off duty.
The main advantage of this valve type is that they provide the same capacity with much lower weight and a shorter face-to-face dimension at large sizes. This valve family consists of series available from 2 in to 72 in, in ASME CL150 to CL1500 pressure classes, for services ranging from cryogenic to high temperature.
In control service, characteristic and rangeability are decisive. Depending on the series, approximately linear, modified equal percentage or equal percentage characteristics are offered, and typical rangeability for all series is 100:1. The same valve can therefore control steadily over a wide flow range, and in most cases no resizing is needed even if flow requirements change after commissioning.
How Is Flow Controlled with a Butterfly Valve?
A butterfly control valve works as a rotary actuator turns the disk shaft. As the disk angle increases, the flow area grows and flow rises.
1. Control signal: The signal from the control system reaches the rotary actuator through a digital valve controller or positioner.
2. Disk rotation: A spring-return diaphragm, double-acting piston or rotary vane actuator turns the disk shaft; a splined actuator-to-valve connection reduces lost motion.
3. Changing flow area: The two flow openings between the disk edges and the body grow with a characteristic that depends on the disk profile.
4. Shutoff: In the closed position the disk edge seats against the seal. Class IV or Class VI shutoff is achieved depending on whether a soft, metal or combination seal is used.
Characteristic and rangeability
In standard high-performance butterfly valves the characteristic is approximately linear or modified equal percentage, depending on the series. In the fully lined series, an approximately equal percentage characteristic is obtained over 90 degrees of rotation with a profiled disk and up to 60 degrees with a conventional disk. Rangeability is typically 100:1.
Expanded-range disk design
For applications where reducing process variability is the priority, a butterfly control valve with a specially developed disk provides an equal percentage characteristic and an expanded control range. This series is offered in 2–36 in, PN 10–40 and CL150–CL600, with wafer and lugged bodies, and gives Class VI shutoff with soft seals and Class IV with metal seals.
Key Features
· Wide rangeability: Typical 100:1 rangeability in all series.
· Very wide size range: From 2 in to 72 in; a compact, light solution at large sizes.
· Body variety: Wafer, lugged and double-flanged bodies; RF, RTJ and buttweld connections.
· Seal options: PTFE, reinforced PTFE, UHMWPE and ETFE soft seals; stainless metal seals; combination metal/polymer seals and cryogenic seals.
· Wide temperature range: Down to -254 °C in cryogenic series and up to 816 °C in high-temperature series.
· Fully lined option: Series with a body fully lined with nitrile or PTFE for corrosive fluids.
· Actuator options: Spring-return diaphragm, double-acting piston and high-cycle rotary vane actuators; digital valve controllers.
· Low-emission packing: Live-loaded packing systems help meet emission requirements.
Technical Specifications
The table summarizes the overall range covered by high-performance butterfly control valve series.
Parameter | Technical data |
Size range | 2–72 in (depending on series) |
Pressure classes | PN 10–40; CL125B, CL150, CL300, CL600, CL900 and CL1500 (depending on series and size) |
Body types | Wafer, lugged, double-flanged |
Connections | Raised face (RF), RTJ, buttweld; 3–24 in ASME B16.5, 30–60 in MSS-SP-44 |
Body materials | WCC carbon steel, CF8M and CF3M stainless steel, EN 1.0619 and 1.4409, cast iron, high-alloy options |
Disk materials | CF8M or CF3M stainless steel, aluminum bronze, S31600; chrome-plated disk edge option |
Temperature range | General series: -46 to 232 °C; precise throttling series: -46 to 454 °C; high-temperature and cryogenic series: -196 / -254 to 816 °C |
Flow characteristic | Approximately linear, modified equal percentage or approximately equal percentage (depending on series) |
Maximum Cv | From 83.7 up to 106,000 depending on series and size |
Rangeability | 100:1 |
Shutoff | Soft seal Class VI; metal seal Class IV; high-pressure and combination seals Class VI; cryogenic seal Class IV or VI |
Expanded-range series | 2–36 in; equal percentage; maximum Cv 60.7–59500 |
Actuators | Spring-return diaphragm, double-acting piston, rotary vane; digital valve controller |
Actuator accessories | Positioner, limit switch, position transmitter, handwheel, travel stops, lock-out device that disables the actuator during maintenance |
Values differ greatly between series; confirm per project with series, size and seal selection.
Key Advantages
· Economy at large sizes: Lower weight, shorter face-to-face and more economical actuation for the same capacity.
· Throttling and on-off in one: The same valve can serve precise throttling and automated on-off duty.
· Wide service range: From cryogenic LNG services to high-temperature lines.
· Tight shutoff: Class VI shutoff with soft and combination seals.
· Flexible installation: Wafer, lugged and double-flanged bodies suit different piping requirements.
Applications
These valves are used for throttling and automated on-off duty across a wide range of process applications.
Large-bore process lines
A compact and economical control valve solution on high-flow liquid and gas lines.
High-temperature services
Throttling service up to 816 °C with high-temperature series.
Cryogenic services
Stainless steel cryogenic valves down to -254 °C for liquefied natural gas and special chemical and hydrocarbon applications.
Corrosive fluids
Throttling and on-off duty in corrosive services requiring tight shutoff with the fully lined series.
Butterfly Control Valve Selection Criteria
The combination of series, seal and actuator is determined by service conditions.
Process and control
· Flow range and required rangeability
· Desired characteristic (linear / equal percentage)
· Pressure drop and cavitation risk
· Process temperature and cryogenic requirement
Body and connection
· Wafer, lugged or double-flanged body
· Pressure class and flange standard
· Body and disk material, corrosion requirement
Seal and actuation
· Required shutoff class and seal type
· Need for bidirectional shutoff
· Actuator type, torque and cycling frequency
· Fail position and maintenance lock requirement
Standards
Main standards used for high-performance butterfly control valves:
Standard / approval | Scope and description |
ASME B16.5 | Flange compatibility for 3–24 in sizes. |
MSS-SP-44 | Flange compatibility for large 30–60 in sizes. |
ASME pressure classes | Body classification from CL125B to CL1500. |
Shutoff classes (Class IV / VI) are defined by seal type; the standard reference should be confirmed in the project documentation
The TLY Enerji Engineering Approach
Using a butterfly control valve on a large line offers significant cost and space advantages when the right series and seal are selected. If disk characteristic, seal temperature limit and actuator torque are not matched, however, control quality and shutoff performance suffer. TLY Enerji addresses these three elements together during selection.
Sizing with process data evaluates the disk angle at normal flow, rangeability and pressure drop. For cryogenic or high-temperature services, body, disk and seal materials are defined according to project conditions, and actuator and digital valve controller selection is included in the quotation. Commissioning and site support needs are added to the project plan; where existing butterfly valves show control instability, disk angle and characteristic are reviewed.
· Series and seal selection
· Sizing and disk angle analysis
· Actuator and controller selection
· Cryogenic / high-temperature material evaluation
· Quotation and documentation
Frequently Asked Questions
Can a butterfly valve be used for control (throttling)?
General-purpose butterfly valves are mostly designed for on-off duty. High-performance butterfly valves, however, are suitable for precise throttling thanks to improved disk profiles and seal systems, and typically offer 100:1 rangeability. Correctly sized, they can be reliable control valves on large lines.
Which characteristic does a butterfly control valve provide?
Depending on the series, approximately linear or modified equal percentage characteristics are offered. In the fully lined series an approximately equal percentage characteristic is obtained over 90 degrees of rotation with a profiled disk. The expanded-range series with a special disk provides an equal percentage characteristic.
Can butterfly valves be used in cryogenic service?
Yes. Stainless steel cryogenic butterfly valve series can be used down to -254 °C in liquefied natural gas and special chemical and hydrocarbon applications. Class IV or Class VI shutoff is achieved depending on the cryogenic seal.
What is the difference between wafer, lugged and double-flanged bodies?
A wafer body is clamped between two line flanges and is the most compact solution. A lugged body has threaded lugs and can be bolted to each flange separately. A double-flanged body connects to the line with its own flanges. Pressure class, piping standard and maintenance needs guide the choice.
Which shutoff classes do butterfly control valves achieve?
Soft seals and combination metal/polymer seals give Class VI, metal seals Class IV. The high-pressure seal provides Class VI, and cryogenic seals provide Class IV or Class VI depending on design. Shutoff requirements should be evaluated together with temperature and pressure.
Which actuators are used with butterfly control valves?
Spring-return pneumatic diaphragm actuators, double-acting pneumatic piston actuators and high-cycle rotary vane actuators can be used. Actuators can be fitted with digital valve controllers, positioners, limit switches and handwheels, and a lock-out device that disables the actuator during maintenance is also available.
