• Quickly Connect Glass and Metal Pipes to KF-Compatible Vacuum Systems
• Options for Pipe Outer Diameters (OD) of 1/4", 3/8", or 1/2"
• 304 Stainless Steel Construction for High Durability and Low Outgassing
• Internal Viton^® Fluoroelastomer O-Ring Included

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 or fused silica optical ports. Each fitting contains an internal Viton fluoroelastomer O-ring. When the knurled cap of the fitting is hand tightened, the O-ring compresses and forms a seal around the inserted pipe. For best results, a thin layer of vacuum grease should be applied to the internal O-ring; along with helping to create a vacuum seal, this grease allows an inserted pipe to slide along the O-ring without catching and causing damage. The knurled cap should not be overtightened, as excessive force could cause O-ring buckling, leading to leaks. The sizes of the internal O-rings are given in the table above. Each flange is shipped with a protective plastic cover.

Viton is a registered trademark of The Chemours Company.

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KF25E90 Elbow Pipe Dimensions

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KF25E45 Elbow Pipe Dimensions

• Straight Pipes or Elbow Joints for KF25 Vacuum Systems
• Tube Diameters
  • Straight Pipes: 0.87" (22.1 mm) ID, 0.99" (25.1 mm) OD
  • Elbow Pipes: 0.87" (22.1 mm) ID, 1.00" (25.4 mm) OD
• 304 Stainless Steel Construction for High Durability and Low Outgassing

We offer straight and angled elbow pipes with KF25 flanges for use when assembling vacuum systems. Details on the angled elbow pipes can be found by clicking on the diagrams to the right. Each flange is protected with a plastic cover during shipping.

• KF25CR-F Centering O-Ring Carrier for KF25 Flanges
  • Holds O-Ring in Place Between KF Flanges
  • Creates Vacuum Seal When Compressed Against KF Mating Surfaces
  • Includes Fluorocarbon O-Ring
• KF25WNC Wing Nut Clamp for KF25 Flanges
  • Secures Two KF25 Flanges Separated by an O-Ring
  • Fast Hand Tightening; No Tools Required

Thorlabs offers a centering O-ring and a wing nut fastening clamp for mating KF25 flanges to a vacuum system. The angled sides of the wing nut clamp compress the O-ring between the flanges, quickly creating a vacuum seal. The wing nut clamp, which has M5 x 0.8 threads, requires only hand tightening, allowing parts to be quickly swapped in and out of a KF-flanged system.

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. Additionally, 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.

We also offer KF16 wing nut clamps and O-rings, as well as KF40 wing nut clamps and O-rings.

• 304 Stainless Steel Construction for High Durability and Low Outgassing
• Blocks Unused Vacuum Ports

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.

We also offer KF16 blank flange caps and KF40 blank flange caps.