Monoflange Innovations: Streamlining Industrial Applications
Monoflange valves, often categorized as an ANSI class product, condense isolation, vent functionality, and leak reduction into a compact design. Their rugged body bolts directly to a process connection or instrument, cutting weight, reducing potential leak paths, and simplifying fabrication.
When you look at how many fittings and valves a traditional hook-up requires, it becomes obvious why plant designers, OEMs, and maintenance teams reach for monoflanges.
A Practical Guide to Monoflange Valves
A monoflange is an integrated valve assembly that replaces multiple components at a process tap. Instead of a separate block valve, bleed valve, and a string of nipples and elbows, you get one forged body with internal passages and seats arranged to perform the same work.
The result is faster installation, cleaner routing, and fewer potential failure points. This single-body concept first gained traction in the offshore oil and gas industries where space and weight carry a premium.
Today, you will find monoflanges across process industries such as chemical and petrochemical sectors that value high integrity, clean layouts, and reliable isolation.
How a Monoflange Works
Inside a monoflange, you typically find two isolation valves and one bleed valve. The internal passages connect a process-side port to an instrument-side port while acting as a connector, providing a safe way to achieve flow isolation and depressurize the cavity.
Operation is straightforward. Close the block valve(s) to isolate, then crack open the bleed to safely depressurize the center cavity. With block and bleed logic, you can test a transmitter, calibrate a gauge, or swap an instrument without disturbing upstream equipment.
Types of Monoflanges
While vendors offer many variations, three core patterns cover most needs.
Single Block and Bleed
One isolation valve and one bleed. Suitable for applications where a single positive shutoff is acceptable.
Double Block and Bleed (DBB)
Two isolation valves in series with a bleed on the cavity between them. Commonly specified in hydrocarbon service and high-pressure systems.
Isolate Only
A compact single block without a separate bleed function. Used where space is tight and maintenance procedures provide an alternate means to depressurize.
| Type | Internal Valves | Typical Use | Pros | Cons |
|---|---|---|---|---|
| Isolate only | 1 block | Simple isolation | Smallest, lightest, lowest cost | No integral depressurization |
| Block and bleed | 1 block + 1 bleed | General service, transmitters | Depressurize cavity, leakage check | Not as secure as DBB |
| DBB | 2 blocks + 1 bleed | Hydrocarbons, high pressure | Higher integrity isolation, maintenance-friendly | Larger body, higher cost |
Applications in Industry
Monoflanges are used wherever instrumentation valves or small-bore isolation are needed at a process tap.
Oil and Gas
Wellheads, separators, meter runs, compressor packages, LACT units, and chemical injection points. Offshore modules value the weight and space savings.
Refining and Petrochemicals
Pressure and level transmitter manifolds, sample points, steam tracing tie-ins, analyzer shelters.
Power Generation
Steam lines, HRSG instrumentation, condensate and feedwater equipment, turbine balance-of-plant tie-ins.
Chemical Processing
Reactor inlets and outlets, specialty gas manifolds, polymer units, and corrosive services where alloy selection matters.
Specialty Gas Service
Hydrogen, ammonia, and oxygen service with designs featuring low fugitive emissions and proper material selection.
Process Industries
Pulp and paper, food and beverage, and water treatment where cleanliness and compact installations help maintain orderly pipe racks.
Technical Features and Specifications
Not all monoflanges are built the same. Look for clear evidence of quality design and traceable materials.
Key Components
- Body and bonnet: Forged A105, A350 LF2 for low temperature, 316/316L stainless steel, duplex and super duplex, or nickel alloys for corrosive service.
- Stems and seats: Non-rotating, hardened tips resist galling. Metal seats for high-temperature and fire-safe service.
- Packing systems: PTFE or graphite packing sets, often live-loaded with Belleville washers.
Safety Features
- Fire-safe options: Packages tested to API 607 or API 6FA for fire resistance.
- Fugitive emissions: Helium leak testing regimes, stem sealing geometries, and low-emission packing.
- Blowout-proof stems: Positive retention prevents stem ejection.
Pressure and Temperature Ratings
Pressure measurement and temperature limits follow both the flange or end connection standard and the internal valve connector design. Always verify with the manufacturer’s datasheet.
| ASME Class | 316/316L Stainless Steel | A105 Carbon Steel |
|---|---|---|
| Class 150 | 275 psi (19 bar) | 285 psi (20 bar) |
| Class 300 | 720 psi (50 bar) | 740 psi (51 bar) |
| Class 600 | 1440 psi (99 bar) | 1480 psi (102 bar) |
| Class 900 | 2160 psi (149 bar) | 2220 psi (153 bar) |
| Class 1500 | 3600 psi (248 bar) | 3705 psi (255 bar) |
| Class 2500 | 6000 psi (414 bar) | 6170 psi (425 bar) |
Temperature Service Windows
PTFE-based and soft seats
Up to 232°C (450°F)
PEEK soft seats
Up to 260°C (500°F)
Graphite packing and metal seats
425-538°C (800-1000°F)
Benefits of Using Monoflanges
Why pick a monoflange with an instrumentation valve over a conventional small-bore assembly? The gains show up during design, installation, operation, and maintenance.
Fewer Leak Paths
One forged body can replace 8 to 12 threaded or flanged joints.
Weight & Space Savings
Up to 60-70% less mass at the nozzle compared to traditional spool.
Faster Installation
Fewer pieces to assemble, fewer gaskets to align.
Cleaner Layouts
Instruments sit closer to process connection, reducing vibration.
Better Isolation Logic
DBB configuration improves safety during maintenance.
Lower Lifecycle Cost
Less hardware to buy, fewer spare parts to stock.
Installation and Maintenance Tips
A well-installed monoflange serves for years with minimal attention. These practices help deliver that outcome.
Planning and Installation
- Verify pressure class, ANSI class, material, end connections, and vent orientation
- Confirm instrument weight and vibration exposure
- Use correct gasket type for the process flange
- Tighten flange bolts in cross pattern and in stages
- Position vent for safe operation and accessibility
Commissioning and Maintenance
- Cycle each valve stage during cold functional testing
- Perform hydrostatic and pneumatic seat tests where specified
- Leak-test threaded joints before releasing to service
- Operate block and bleed stages periodically
- Replace soft seats and packing on defined interval
Frequently Asked Questions
What is the difference between DBB and DIB in this context?
DBB stands for double block and bleed, two isolation valves with a bleed between. DIB, double isolation and bleed, can imply two separate seating barriers on one or both sides. In small-bore monoflanges, vendors typically use DBB for two valves in series with a bleed port.
Can a monoflange replace a traditional instrument manifold?
In many cases, yes. For a single transmitter, a DBB monoflange with an instrumentation valve gives isolation and vent functions similar to a two-valve manifold.
Are monoflanges suitable for gas and liquid service?
Yes. Seat selection and materials should match the media. Soft seats deliver bubble-tight shutoff on gases, while metal seats suit high-temperature liquids.
How do I choose between needle and ball trims?
Ball valves give quick on-off action and higher flow. Needle valves give fine control and more precise throttling near shutoff.
Do I need a vent-to-safe-area connection?
If the media is hazardous, yes. Many facilities require routing to a flare or recovery header. For benign media, a local vent may be acceptable.
Can monoflanges be installed vertically and horizontally?
Orientation is flexible. Keep the vent port accessible and ensure any captured liquid can drain safely.
What pressure class should I pick?
Match the connected flange rating and the maximum design pressure. For general service, Class 600 and Class 900 are common. Confirm with the process engineer and equipment datasheet.
Technical Resources
Download our comprehensive technical documentation to learn more about our monoflange solutions.
Technical Brochure
Complete technical specifications, material options, and selection guide for monoflange valves.
Sample Drawing
Dimensional drawings and installation diagrams for standard monoflange configurations.
Request a Quote
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