Choosing the right vacuum flange hinges on understanding the distinct applications and performance capabilities of ISO-KF, ISO (ISO-K/ISO-F), JIS, and CF types. While ISO-KF offers quick assembly for rough vacuum, CF flanges dominate ultra-high vacuum with metal seals, and ISO/JIS serve specific industrial or regional needs.
Understanding ISO-KF Flanges: The Quick-Connect Standard?
ISO-KF flanges, also known as NW or Klein Flange, are the quick-connect workhorse for small to medium vacuum systems, typically operating from rough to high vacuum (10⁻³ to 10⁻⁷ mbar). They use a simple clamp and elastomer O-ring for a leak-tight seal, making them ideal for rapid assembly and frequent system modifications.
Typically, these flanges are made from stainless steel 304 or 316, which provides excellent corrosion resistance, crucial for maintaining vacuum integrity. They come in a standard size range from DN10 to DN50, with DN16, DN25, and DN40 being the most common sizes found on rotary vane pumps and other lab equipment. For instance, a DN25 flange pairs perfectly with a 25.4 mm diameter hose (with a 1.65 mm wall thickness).
While ISO-KF flanges are a fantastic choice for many applications, it is important to remember their main limitation: the elastomer O-ring. This O-ring material limits the bakeout temperature, typically to around 150°C, which means ISO-KF flanges are generally unsuitable for ultra-high vacuum (UHV) scenarios that require much higher bakeout temperatures to achieve extreme cleanliness.
ISO-KF Flange Key Features and Applications
| Feature | Description | Application Fit |
|---|---|---|
| Sealing Mechanism | Clamp with elastomer O-ring & centering ring | Quick assembly, frequent modifications |
| Pressure Range | Rough to High Vacuum (10⁻³ to 10⁻⁷ mbar) | General lab use, pump connections, small chambers |
| Bakeout Temperature | Limited (~150°C) due to O-ring | Not suitable for UHV or extreme cleanliness requirements |
| Common Sizes | DN10 to DN50 (DN16, DN25, DN40 popular) | Versatile for smaller components and pumps |
Exploring ISO Flanges: Are ISO-K and ISO-F Right for Your System?
ISO flanges (LF/LFB/MF) are designed for larger, more permanent vacuum installations, typically starting from DN63. They come in two main subtypes: ISO-K, which uses double-claw clamps for assembly, and ISO-F, which relies on bolted connections, offering robust and reliable sealing solutions for high-vacuum industrial applications.
ISO-K (Klar flange) systems utilize double-claw clamps that latch into grooves on the tubing. This clamp-based design still allows for relatively quick assembly and disassembly compared to bolted flanges, making them suitable for sections of a large system that might require occasional modification or servicing. They are typically used in high-vacuum setups requiring moderate bakeout temperatures (up to 200°C), slightly higher than KF due to a different O-ring seating.
ISO-F (Flange type), on the other hand, relies on bolted connections with O-rings. This bolted design provides superior strength and vibration resistance, making ISO-F flanges preferred for critical components like large gate valves, pumps, or wall-mounted systems where permanent, vibration-resistant sealing is a top priority. They are common in industrial systems such as semiconductor manufacturing, where absolute reliability and long-term stability are paramount. Both ISO-K and ISO-F start at DN63, with common sizes ranging up to DN500, making them suitable for large-diameter vacuum lines. For example, a DN63 flange is designed to connect to a 50.8 mm diameter hose (with a 1.65 mm wall thickness).
ISO Flange Types: K vs. F Comparison
| Type | Sealing Mechanism | Typical Use Case | Pros | Cons |
|---|---|---|---|---|
| ISO-K | Double-claw clamps with O-ring | Moderate bakeout, occasional disassembly | Faster assembly than bolted, larger sizes than KF | O-ring limits UHV, less rigid than bolted |
| ISO-F | Bolted connections with O-ring | Permanent installations, high vibration, gate valves | Superior rigidity, vibration resistance | Slower assembly/disassembly, O-ring limits UHV |
Delving into CF Flanges: Why Are They the UHV Champion?
CF (ConFlat) flanges are the undisputed champion for ultra-high vacuum (UHV) systems, achieving pressures below 10⁻⁹ mbar. They utilize a specialized knife-edge design that bites into soft copper gaskets, creating a metal-to-metal seal capable of withstanding extreme bakeout temperatures up to 450°C, crucial for minimizing outgassing.
The capability to withstand high bakeout temperatures is a primary reason for CF flanges’ dominance in UHV. Components in UHV systems must be heated to hundreds of degrees Celsius (up to 450°C for CF) to drive off adsorbed gases and moisture from their surfaces. Elastomer seals would simply degrade at these temperatures, releasing contaminants. CF flanges, typically made of stainless steel 304 or 316, can handle these extreme bakeouts, ensuring minimal outgassing and achieving the lowest possible pressures. CF flanges are available in a range of sizes from DN10 to DN250.
While OFHC copper is the standard gasket material, Viton or PTFE gaskets can be used for lower-temperature applications if UHV is not strictly required. However, for true UHV performance, copper gaskets are mandatory and must be replaced after each disassembly to maintain seal integrity.
CF Flange Characteristics for Ultra-High Vacuum
| Feature | Description | UHV Impact |
|---|---|---|
| Sealing Method | Metal knife-edge compressing soft copper gasket | Creates hermetic, virtually leak-proof seal |
| Pressure Range | Ultra-High Vacuum (below 10⁻⁹ mbar) | Essential for most demanding vacuum applications |
| Bakeout Capability | Withstands up to 450°C | Enables extreme cleanliness by removing adsorbed gases |
| Gasket Replacement | Copper gaskets must be replaced after each use | Ensures consistent high-integrity sealing |
How Do JIS Flanges Compare to Other Standards?
Japan’s JIS B 2290 standard defines VF (flat) and VG (gasketed) flanges, emphasizing modular design and offering reliable seals from 10⁻² to 10⁻⁸ mbar. While less common globally than ISO or CF, JIS flanges are crucial for compatibility with specific Japanese industrial equipment and can be found in both aluminum and stainless steel variants.
JIS flanges are effective across a pressure range from 10⁻² to 10⁻⁸ mbar, placing them in the rough to high vacuum categories, similar to the broader ISO range. They are available in materials like aluminum or stainless steel, depending on the specific thermal and corrosion resistance needs of the application. Aluminum variants, for instance, are lighter, which can be advantageous for portable vacuum setups or systems where weight is a concern. While not as universally adopted as ISO-KF or CF flanges, JIS flanges shine in specific niches.
They are particularly relevant when working with Japanese-manufactured equipment or systems that require compatibility with legacy industrial tools following this standard. Knowing about JIS flanges ensures you can correctly integrate components when faced with non-ISO or non-CF systems.
JIS Flange Characteristics and Comparisons
| Feature | Description | Comparison to ISO/CF |
|---|---|---|
| Standard | Japanese Industrial Standard (JIS B 2290) | Regional standard, less global than ISO/CF |
| Types | VF (flat) and VG (gasketed) | Offers modularity similar to some ISO principles |
| Pressure Range | 10⁻² to 10⁻⁸ mbar | Covers similar range to ISO, lower than CF |
| Materials | Aluminum or Stainless Steel | Similar material options to ISO, wider use of Aluminum |
| Primary Use | Japanese-manufactured equipment, legacy systems | Niche market, specific compatibility needs |
Final Thoughts
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