What Is a Butterfly Isolation Valve?
An isolation valve is used to separate a section of line from the process for maintenance, circuit changes or emergencies. The key performance expected from it is zero leakage when closed and reliable operation when needed. Butterfly valves are widely used for isolation because at large sizes they offer low weight, a short face-to-face dimension and fast quarter-turn operation.
Unlike general-purpose butterfly valves, high-performance butterfly valves are designed for higher pressure classes, wider temperature ranges and tighter shutoff classes. Depending on the series, the seal system consists of polymers such as PTFE, reinforced PTFE, UHMWPE or ETFE, of stainless metal seals, or of combination designs that use metal and polymer together.
These valves can be used in automated on-off service with spring-return or double-acting actuators and can also throttle when needed. The fully lined series offers an economical alternative to alloy bodies for corrosive fluids, while cryogenic and very high-pressure series make isolation possible under service conditions that standard butterfly valves cannot handle.
How Does a Butterfly Valve Shut Off?
A butterfly valve opens and closes with a quarter turn. In the closed position the disk edge contacts the seal, and sealing takes place along this contact line.
1. Open position: The disk is parallel to the flow, which passes on both sides of the disk.
2. Closing movement: An actuator or manual operator rotates the disk shaft until the disk is perpendicular to the flow.
3. Seating against the seal: The disk edge seats in the seal in the body. Seal type and material determine the achievable shutoff class and temperature limit.
4. Holding the closed position: The actuator maintains the predefined position on failure; a lock-out device that disables the actuator during maintenance can be selected.
Shutoff class by seal type
Soft seals and combination metal/polymer seals give Class VI shutoff. Metal seals offer Class IV and are used at higher temperatures. The high-pressure seal gives Class VI. Cryogenic seals provide Class IV or Class VI depending on design. The general series used from -46 to 232 °C offers bidirectional Class VI shutoff, and the fully lined series gives Class VI.
Automated on-off and safe maintenance
Spring-return diaphragm, double-acting piston and high-cycle rotary vane actuators can be used for automated on-off duty. Accessories such as limit switches, position transmitters and handwheels allow valve position monitoring and manual intervention when needed.
Key Features
· Class VI shutoff: Tight shutoff with soft, combination and high-pressure seals.
· Bidirectional shutoff: Class VI shutoff in both flow directions in the general series.
· Fully lined series: Body fully lined with nitrile or PTFE; for corrosive and toxic fluids.
· Cryogenic series: Isolation down to -254 °C with stainless steel body and disk.
· High-pressure option: Bodies up to CL900 and CL1500; Class VI with the high-pressure seal.
· Body variety: Wafer, lugged and double-flanged bodies; RF, RTJ and buttweld connections.
· Maintenance lock: Option for a lock-out device that disables the actuator during maintenance.
Specifications by Series and Seal
Shutoff-oriented summary of butterfly isolation valve series:
Parameter | Technical data |
General series | 3–12 in, wafer, CL150 / CL300; -46 to 232 °C; PTFE seal; bidirectional Class VI |
Precise series | 2–12 in, lugged (wafer in 2 in) and double-flanged; PN 10–40, CL150 / CL300; -46 to 454 °C; soft seal Class VI, metal seal Class IV |
High-pressure series (CL600) | 3–24 in, lugged and double-flanged; ETFE soft seal Class VI; metal seal Class IV; high-pressure and combination seals Class VI |
Large-bore / high-temperature series | 14–48 in; wafer, lugged, double-flanged; CL150 / CL300; -196 to 816 °C; soft and combination seals Class VI |
Very high-pressure series | CL600: 30–48 in; CL900: 6–36 in; CL1500: 10–20 in; -254 to 816 °C; high-pressure seal Class VI |
Fully lined series | 2–12 in, wafer; PN10, PN13, CL125B, CL150, CL300; nitrile or PTFE liner; Class VI |
Cryogenic series | Down to -254 °C; CF8M body and disk; cryogenic seal Class IV or VI |
Connections | RF, RTJ, buttweld; 3–24 in ASME B16.5, 30–60 in MSS-SP-44 |
Body materials | WCC, CF8M, CF3M, EN 1.0619 / 1.4409, cast iron (lined series), high-alloy options |
Actuators | Spring-return diaphragm, double-acting piston, rotary vane; manual operator |
Actuator temperature ranges | Options between -60 and 149 °C depending on actuator type |
Shutoff class, pressure and temperature limits must be confirmed per project by series, size and seal combination.
Key Advantages
· Reliable isolation: Safe separation of line sections with Class VI shutoff.
· Fast operation: Quick on-off operation with quarter-turn motion and automated actuation.
· Economy at large sizes: Low weight, short face-to-face and small actuator requirement.
· Suited to difficult fluids: Lined, cryogenic and high-pressure series for a wide range of applications.
· Safe maintenance: Actuator lock-out device and position monitoring accessories.
Applications
High-performance butterfly isolation valves are used for automated on-off duty and tight shutoff in many process applications.
General process isolation
Automated on-off on liquid and gas lines; points requiring bidirectional Class VI shutoff.
Corrosive and toxic fluids
Tight shutoff without an alloy body using the fully lined series.
Cryogenic isolation
Down to -254 °C for liquefied natural gas and special chemical and hydrocarbon applications.
High pressure and temperature
Isolation in CL900–CL1500 classes and services up to 816 °C.
Butterfly Isolation Valve Selection Criteria
For an isolation valve, the priority is that the required shutoff performance is maintained throughout the service conditions.
Shutoff requirement
· Required shutoff class (Class IV / VI)
· One- or two-directional shutoff
· Shutoff pressure differential
Service conditions
· Temperature range and seal material compatibility
· Presence of corrosive or toxic fluids
· Cryogenic requirement
· Pressure class
Installation and operation
· Wafer, lugged or double-flanged body
· Manual or automated operation, fail position
· Cycling frequency and actuator type
· Need for maintenance lock and position monitoring
Standards
Flange and pressure classification of butterfly isolation valves follows these standards:
Standard / approval | Scope and description |
ASME B16.5 | Flange compatibility for 3–24 in. |
MSS-SP-44 | Flange compatibility for large 30–60 in sizes. |
ASME pressure classes | Body classification from CL125B to CL1500. |
Shutoff test standard and certificates must be confirmed with the project documentation.
TLY Enerji Isolation Solutions
The expectation from an isolation valve is simple: no leakage when closed and safe operation when needed. Meeting it depends on seal material compatibility with temperature and fluid, body type suitability for the piping and the right choice of actuator fail position. TLY Enerji evaluates these three elements together.
Shutoff class, need for bidirectional shutoff and maintenance scenarios are clarified with process and line data, and a suitable combination of series, seal and actuator is presented with its technical justification. Material compatibility is reported separately for cryogenic or corrosive services. Quotation, documentation and commissioning support are planned according to project scope; for projects with many isolation points across a plant, standardization of series and seals is proposed to simplify spare parts management.
· Shutoff requirement analysis
· Series and seal selection
· Actuator and fail position definition
· Material compatibility evaluation
· Quotation and documentation
Frequently Asked Questions
Are butterfly valves suitable for isolation?
With the right seal choice, high-performance butterfly valves are a reliable option for isolation. Class VI shutoff can be achieved with soft, combination and high-pressure seals. Low weight and a short face-to-face dimension at large sizes make butterfly valves an economical isolation solution.
What is bidirectional shutoff and which series offer it?
Bidirectional shutoff means the valve provides the same leakage class whichever side the pressure comes from. The general series used between -46 and 232 °C offers bidirectional Class VI shutoff. For other series, the need for bidirectional shutoff should be evaluated per project together with seal type and installation direction.
When is a fully lined butterfly valve preferred?
With corrosive or toxic fluids, all wetted surfaces of the body are lined with nitrile or PTFE. This design offers an economical alternative to valves with alloy bodies and gives Class VI shutoff. The lined series is available in 2–12 in with a wafer body.
What is the difference between a metal seal and a soft seal?
Soft seals (PTFE, reinforced PTFE, UHMWPE, ETFE) give Class VI shutoff, but their temperature limits are set by the polymer. Metal seals can operate at higher temperatures and provide Class IV shutoff. Combination metal/polymer seals bring together the advantages of both and give Class VI shutoff.
Can butterfly valves be used for cryogenic isolation?
Yes. Cryogenic butterfly valve series with stainless steel body and disk can be used down to -254 °C in liquefied natural gas and special chemical and hydrocarbon applications. Class IV or Class VI shutoff is provided depending on the cryogenic seal design.
Can a high-performance butterfly valve be chosen instead of a triple offset valve?
It depends on service conditions. Soft-seated high-performance butterfly valves provide Class VI shutoff and an economical solution at moderate temperatures. For services that require metal-to-metal seating, fire resistance and zero visible leakage at very high temperatures, triple offset butterfly valves should be evaluated.