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KF-Flanged Components and Accessories
KF25 Flange to Ø0.375" Compression Fitting Adapter
KF25 Wing Nut Clamp
A KF25C050 Compression Fitting is used to add an empty glass cell to a KF-compatible vacuum system.
KF16 Flange to G1/4" Thread Adapter
KF16 Blank Flange
The animation above illustrates how a vacuum seal is achieved using KF Flanges.
KF flanges are ISO-standardized vacuum fittings that provide a vacuum seal by compressing a rubber O-ring between two mating surfaces. Also referred to as NW, QF, or DN flanges, KF flanges are ideal for quickly assembling vacuum systems thanks to their ease of use, maintenance, and reusability.
Thorlabs offers fittings to adapt KF25-flanged components to pipes with outer diameters of 0.250", 0.375", or 0.500" via a compression fitting. Thread adapters are also available to mate British Standard Pipe Parallel (BSPP) or double ferrule compression fittings to KF16 vacuum components. These adapters and other components can be mated to a vacuum system using wing nut clamps and O-ring carriers. Our wing nut clamps and O-ring carriers, as well as our blank caps are available in KF16, KF25, and KF40 sizing. Key dimensions of these KF flanges can be found by visiting the KF Flange Sizes tab. Our in-house machine shop allows us to modify or customize components with any standard KF flange. To submit a request, please contact Tech Support.
For best performance, a very thin coating of vacuum grease should be applied to any O-ring used in a KF system. This should be done by hand while wearing gloves, leaving just enough grease to cause the O-ring to shine. The O-ring and its mating surfaces should be visually inspected before installation to ensure there is no debris which may prevent proper contact and cause a leak. O-rings should be regularly inspected to spot dry rot, cracking, tearing, or accumulation of debris from normal operation. Replace any O-ring suspected of causing a leak.
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Thorlabs KF40 Flange Measurements
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Thorlabs KF25 Flange Measurements
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Thorlabs KF16 Flange Measurements
KF Flange Sizes
KF flanges are defined by ISO 2861 Clamped-Type Quick-Release Couplings. This specification details the dimensions and tolerances for the five standard KF flange sizes: 10 mm, 16 mm, 25 mm, 40 mm, and 50 mm. These sizes are the nominal bore size of the flanged pipe. The name "KF" derives from the German phrase "Klein Flansche," literally translating to "small flange"; this name was used around the time of the flange's adoption by ISO and DIN, as flanges for pipes larger than 50 mm are more appropriately handled by flanges that deform metal gaskets to create a seal, like CF flanges.
Thorlabs offers from stock 16 mm, 25 mm, and 40 mm KF components and accessories. The dimensions of our flanges are shown in the diagrams to the right. Our in-house machine shop allows us to modify or customize components with any standard KF flange. To submit a request, please contact Tech Support.
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The double ferrule fitting on Thorlabs' Herriott Cells (left) can be replaced with the KF16G25E vacuum flange adapter (right). Note that the leakage rate of the Herriott Cell is not guaranteed if the gas fitting is replaced or adjusted by the user.
The KF16 Flange to G1/4" External Threading Adapter allows vacuum systems to be connected to British Standard Pipe Parallel (BSPP) components. The interior diameter of our adapter is Ø9.0 mm (Ø0.35"). The included rubber gasket is pre-installed onto the part; removing the gasket is not recommended, as it may become damaged. The exterior flats for tightening accept a 14 mm (9/16") wrench. Each flange is shipped with a protective plastic cover.
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KF16PC25 adapter shown with double ferrule compression fittings. The ferrules and compressing nut are not included with the KF16PC25 or KF16PC6/M.
These adapters allow KF16 vacuum systems to be connected to double ferrule compression fittings, making them compatible with Swagelok®-brand fittings. The image to the right shows how the KF16PC25 adapter interfaces with compression fittings; note the ferrule, washer, and nut are not included in the purchase of a double ferrule compression adapter. The KF16PC25 adapter accepts Ø1/4" metal tubes, and the KF16PC6/M adapter accepts Ø6 mm metal tubes; the hex on each adapter accepts 9/16" (14 mm) wrenches. Each flange is shipped with a protective plastic cover.
KF25 flanges with compression fittings mount smooth-surfaced pipes to vacuum systems, including metal tubes, such as those used for gas lines, or glass tubes like those found on our empty glass cells. Each fitting contains an internal Viton fluoroelastomer
Viton is a registered trademark of The Chemours Company.
Wing nut fastening clamps fit around an assembly of two KF flanges separated by an O-ring. The angled sides of the clamp compress the O-ring between the flanges, quickly creating a vacuum seal. These components only require hand tightening the wing nut (M5 x 0.8), without the need for additional tools, allowing parts to be quickly swapped in and out of a KF-flanged system.
Be aware that under vacuum pressure, the KF connection may undergo additional compression, causing the wing nut clamp to loosen. Some additional tightening may be performed, but be careful not to overtighten the clamp, as the wing nut may become difficult to remove or jammed when the system returns to atmospheric pressure. Do not remove a wing nut clamp while a system is under vacuum.
O-ring carriers keep O-rings centered between KF flange components during the clamping process. Carriers are available in KF16, KF25, and KF40 sizes; each include a single fluorocarbon O-ring sized appropriately for the corresponding flange size.
For best performance, a very thin coating of vacuum grease should be applied to the O-ring before installation. This should be done by hand while wearing gloves, leaving just enough grease to cause the O-ring to shine. The O-ring and its mating surfaces should be visually inspected before installation to ensure there is no debris which may impede proper contact and cause a leak. O-rings should be regularly inspected to spot dry rot, cracking, tearing, or accumulation of debris from normal operation. Replace any O-ring that is suspected of causing a leak.
Stainless steel KF flange blank caps can be used to protect a vacuum assembly that is not attached to a vacuum system, to block a port during leak testing, or to cap off a port that is not being used on a vacuum chamber body. Each cap is shipped with a protective plastic cover.