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DN35CF-DN40CF (2.75″ OD) 304L SS Standard ConFlat® (CF) UHV Flanges

TFM Flange System for High Vacuum and UHV Applications

The TFM flange system is a popular choice for high vacuum and ultra-high vacuum (UHV) applications due to its reliability and versatility. A wide range of vacuum components, such as gauges, instruments, feedthroughs, and accessories, are compatible with this flange system, making it highly adaptable for various setups.

Blank (Blind) Flanges: Purpose and Customization

A blank (or blind) flange is a solid, disc-shaped component that is commonly used to close off unused sections of tubing or ports in vacuum systems. These flanges can also be machined to create custom fittings, providing flexibility in system design and modification.

Sealing Mechanism of TFM Flanges

TFM flanges utilize a knife-edge sealing mechanism, with the knife-edge being slightly recessed below the flat surface of the flange. When the bolts of the flange pair are tightened, the knife-edges create annular grooves in a soft metal gasket, causing the gasket material to deform and fill surface imperfections on the flange. This results in a leak-tight seal. TFM seals can maintain vacuum conditions ranging from atmospheric pressure (760 torr or 103 mbar) down to < 1 x 10^-13 torr (< 1.3 x 10^-13 mbar). Depending on the materials used, the system can function effectively within a temperature range of -196°C to 450°C.

Flange Size Nomenclature

In North America, TFM flange sizes are typically referenced by their outer diameter (O.D.). However, in Europe and parts of Asia, the nominal internal diameter (nominal I.D.), which refers to the largest tube that can be welded to the bored flange, is used more frequently.

Types of TFM Flanges

TFM flanges are available in several versions, designed to meet different system needs:

Fixed Flange

A fixed flange consists of a single-piece design where the bolt-hole orientation is fixed relative to the fitting. This type is suitable for systems requiring a specific bolt alignment.

Rotatable Flange

A rotatable flange is composed of two parts: an inner weld ring and an outer bolt ring. The bolt ring can rotate around the weld ring, allowing for easier alignment of bolt holes during installation, which is particularly useful in complex assemblies.

Both fixed and rotatable flanges can be supplied with either through (clearance) holes or tapped holes, providing a range of options depending on installation requirements.

Applications of TFM Flanges

TFM flanges are widely used across industries requiring high or ultra-high vacuum conditions. Their robust sealing capabilities and adaptability make them essential in sectors like semiconductor manufacturing, materials research, and scientific instrumentation.

Through (Clearance) Holes

Are through-holes that allow adequate clearance for bolts to go through both flanges and secured by nuts or plate nuts.

Tapped Holes

Are imperial or metric threaded holes machined through the flange. This allows a clearance-hole flange to be connected without the need for nuts or plate nuts. Be aware of a components bolt hole orientation when selecting tapped flanges.

Ordering Table 

Flange Size/OD Type Flange Material Drawing Nominal Tube OD Bore Counter Bore Thickness Bolt Circle Dia. Bolt Hole Dia. # of Bolt Holes Thread Size Part Number
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip — Blank — 0.50 2.312 0.265 6 — F0275X000N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip — Blank — 0.50 2.312 — 6 M6 x 1.0P F0275X000NM
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip — Blank — 0.50 2.312 — 6 1/4-28 F0275X000NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip — Blank — 0.50 2.312 0.265 6 — F0275X000R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip — Blank — 0.50 2.312 — 6 M6 x 1.0P F0275X000RM
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip — Blank — 0.50 2.312 — 6 1/4-28 F0275X000RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 1/4 0.255 — 0.50 2.312 0.265 6 — F0275X025N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1/4 0.255 — 0.50 2.312 — 6 1/4-28 F0275X025NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 1/4 0.255 — 0.50 2.312 0.265 6 — F0275X025R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1/4 0.255 — 0.50 2.312 — 6 1/4-28 F0275X025RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 3/8 0.380 — 0.50 2.312 0.265 6 — F0275X037N
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 1/2 0.505 — 0.50 2.312 0.265 6 — F0275X050N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1/2 0.505 — 0.50 2.312 — 6 1/4-28 F0275X050NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 1/2 0.505 — 0.50 2.312 0.265 6 — F0275X050R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1/2 0.505 — 0.50 2.312 — 6 1/4-28 F0275X050RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 5/8 0.63 — 0.50 2.312 0.265 6 — F0275X062N
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 3/4 0.72 0.760 0.50 2.312 0.265 6 — F0275X075N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 3/4 0.72 0.760 0.50 2.312 — 6 1/4-28 F0275X075NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 3/4 0.72 0.770 0.50 2.312 0.265 6 — F0275X075R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 3/4 0.72 0.770 0.50 2.312 — 6 1/4-28 F0275X075RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 1 0.94 1.010 0.50 2.312 0.265 6 — F0275X100N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1 0.94 1.010 0.50 2.312 — 6 M6 x 1.0P F0275X100NM
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1 0.94 1.010 0.50 2.312 — 6 1/4-28 F0275X100NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 1 0.94 1.020 0.50 2.312 0.265 6 — F0275X100R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1 0.94 1.020 0.50 2.312 — 6 1/4-28 F0275X100RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 1-1/4 1.19 1.260 0.50 2.312 0.265 6 — F0275X125N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1-1/4 1.19 1.260 0.50 2.312 — 6 1/4-28 F0275X125NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 1-1/4 1.19 1.270 0.50 2.312 0.265 6 — F0275X125R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1-1/4 1.19 1.270 0.50 2.312 — 6 1/4-28 F0275X125RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 1-1/2 1.44 1.510 0.50 2.312 0.265 6 — F0275X150N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1-1/2 1.44 1.510 0.50 2.312 — 6 M6 x 1.0P F0275X150NM
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1-1/2 1.44 1.510 0.50 2.312 — 6 1/4-28 F0275X150NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 1-1/2 1.44 1.520 0.50 2.312 0.265 6 — F0275X150R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1-1/2 1.44 1.520 0.50 2.312 — 6 M6 x 1.0P F0275X150RM
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1-1/2 1.44 1.520 0.50 2.312 — 6 1/4-28 F0275X150RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 1-5/8 1.56 1.635 0.50 2.312 0.265 6 — F0275X162N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1-5/8 1.56 1.635 0.50 2.312 — 6 M6 x 1.0P F0275X162NM
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1-5/8 1.56 1.635 0.50 2.312 — 6 1/4-28 F0275X162NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 1-5/8 1.56 1.645 0.50 2.312 0.265 6 — F0275X162R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1-5/8 1.56 1.645 0.50 2.312 — 6 M6 x 1.0P F0275X162RM
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1-5/8 1.56 1.645 0.50 2.312 — 6 1/4-28 F0275X162RT
DN35CF-DN40CF (2.75" OD) Fixed 304L SS Tooltip 1-3/4 1.63 1.760 0.50 2.312 0.265 6 — F0275X175N
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1-3/4 1.63 1.760 0.50 2.312 — 6 M6 x 1.0P F0275X175NM
DN35CF-DN40CF (2.75" OD) Fixed Tapped 304L SS Tooltip 1-3/4 1.63 1.760 0.50 2.312 — 6 1/4-28 F0275X175NT
DN35CF-DN40CF (2.75" OD) Rotatable 304L SS Tooltip 1-3/4 1.63 1.770 0.50 2.312 0.265 6 — F0275X175R
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1-3/4 1.63 1.770 0.50 2.312 — 6 M6 x 1.0P F0275X175RM
DN35CF-DN40CF (2.75" OD) Rotatable Tapped 304L SS Tooltip 1-3/4 1.63 1.770 0.50 2.312 — 6 1/4-28 F0275X175RT

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FAQ

Tube fittings are designed for tubes (measured by outside diameter and wall thickness) used in high-pressure and instrumentation applications, whereas pipe fittings are for pipes (identified by nominal pipe size) primarily used in fluid transport.

 

Common valve types include ball valves, gate valves, check valves, butterfly valves, and globe valves. Each serves a specific function—from quick shutoff (ball/gate valves) to flow regulation (globe valves).

 

  • For tubing, measure the outside diameter; for pipes, refer to the nominal pipe size (using conversion charts if needed). Always match the valve or fitting size to your pipe’s dimensions and flow requirements.

  • Frequently used thread types include NPT (National Pipe Tapered), BSP (British Standard Pipe), and UNC, along with slip-fit options that rely on compression or fusion rather than threads.

Interchangeability depends on manufacturer specifications and certification. Always verify compatibility via manufacturer guides or certified interchangeability charts.

 

  • A coupling is a short, straight fitting used to join two pipes or tubes. It provides a secure, leak-tight connection and can sometimes serve to extend or repair piping runs.

Consider valve type, pressure and temperature ratings, material compatibility with your fluid, actuation method (manual or automatic), and maintenance requirements.

 

  • Valves regulate flow by opening, closing, or partially obstructing the pathway. Their mechanisms (such as the rotation of a ball or the linear movement of a gate) determine the speed and precision of flow control.

  • A flange is a flat, circular component used to connect pipes, valves, or other equipment. Bolted together with gaskets, flanges provide a secure, leak-proof joint that facilitates both assembly and maintenance.

  • Manual valves require physical operation via handles or levers, whereas actuated valves use mechanisms—pneumatic, electric, or hydraulic—to open and close automatically or remotely.

  • Issues include leaks caused by improper installation, over-tightening, degraded seals, material incompatibility, and fatigue from repeated cycling. Regular inspection and proper installation practices help mitigate these problems.

Regular maintenance involves periodic inspections, cleaning or replacing worn seals, ensuring proper torque during installation, and adhering to manufacturer guidelines and local plumbing codes to preserve system integrity.

 

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