When building or maintaining vacuum systems, selecting the right flange type is critical. With multiple standards available, confusion often arises even among professionals. This guide explores the most widely used vacuum flange types, their applications, and practical considerations to help you make informed decisions.
1. ISO-KF (NW) Flange: The Quick-Connect Workhorse
ISO-KF flanges (also called NW or Klein Flange) dominate small to medium vacuum setups due to their simplicity and speed. Instead of bolts, a circular clamp compresses a centering ring and elastomer O-ring to create a leak-tight seal. This design allows rapid assembly and disassembly, making them ideal for labs or production lines where frequent modifications occur.
Key details:
- Size range: DN10 to DN50 (DN16, DN25, and DN40 are most common for rotary vane pumps).
- Material: Typically stainless steel 304 or 316 for corrosion resistance.
- Hose compatibility: A DN25 flange pairs with a 25.4 mm diameter hose (1.65 mm wall thickness).
When to choose ISO-KF:
Use these for rough to high vacuum applications (10⁻³ to 10⁻⁷ mbar) where convenience matters, such as connecting pumps, gauges, or small chambers. Avoid ultra-high vacuum (UHV) scenarios—the elastomer O-ring limits bakeout temperatures to ~150°C.
2. ISO Flanges: Heavy-Duty Solutions for Complex Systems
ISO flanges (LF/LFB/MF) cater to larger, permanent installations. Two subtypes exist:
- ISO-K (Klar flange): Uses double-claw clamps that latch into grooves on the tubing.
- ISO-F (Flange type): Bolted connections with O-rings, preferred for gate valves or wall-mounted systems.
Key details:
- Size starts at DN63, with DN63 to DN500 being standard.
- Hose pairing: A DN63 flange connects to a 50.8 mm diameter hose (1.65 mm wall thickness).
When to choose ISO:
Opt for ISO-K in high-vacuum setups requiring moderate bakeout temperatures (up to 200°C). ISO-F suits industrial systems where vibration resistance and permanent sealing are priorities, such as semiconductor manufacturing.
3. JIS VF/VG Flanges: Japan’s Answer to Modular Design
Japan’s JIS B 2290 standard (VF/VG flanges) emphasizes modularity. The “VF” (flat) and “VG” (gasketed) variants use interlocking grooves and copper gaskets for reliable seals in vacuum distribution lines.
Key details:
- Materials: Aluminum or stainless steel, depending on thermal and corrosion needs.
- Pressure range: Effective from 10⁻² to 10⁻⁸ mbar.
When to choose JIS:
These flanges shine in Japanese-manufactured equipment or systems requiring compatibility with legacy industrial tools. Their lightweight aluminum variants suit portable vacuum setups.
4. CF Flanges: The Ultra-High Vacuum Champion
ConFlat (CF) flanges are the gold standard for UHV systems (below 10⁻⁹ mbar). Unlike elastomer seals, they use a knife-edge design that bites into soft copper gaskets, creating a metal-to-metal seal.
Key details:
- Materials: Stainless steel 304/316, capable of withstanding 450°C bakeouts.
- Sizes: DN10 to DN250.
- Gaskets: Oxygen-free copper (OFHC) is standard; Viton or PTFE suits lower-temperature applications.
When to choose CF:
Mandatory for particle accelerators, space simulation chambers, or any system requiring extreme cleanliness and minimal outgassing. Replace copper gaskets after each disassembly to prevent leaks.
Reference: Wikipedia
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