Technical insight
CF or KF Vacuum Flange? Define the Sealing Interface Before an RFQ
For a custom vacuum housing or flanged component, specify the flange family and complete mating interface before requesting a quote. CF and KF refer to different connection arrangements; do not reduce either to a port diameter. Ask the customer's technical reviewer to approve the seal, mating part and fastening definition together.
By Geetai Precision
- Published
- Updated
Begin with the sealing arrangement
Kurt J. Lesker's CF technical notes describe a seal formed when opposing flange knife edges indent a soft metal gasket as the flange bolts are tightened.
Lesker describes KF trapped centering-ring assemblies as using an O-ring and outer ring between two flanges, secured with a clamp. Its KF range also includes other centering-ring arrangements.
These descriptions explain the connection families; they do not select a seal for a particular pump or prescribe assembly instructions. The checklist below is original buyer guidance for resolving an interface definition. Use the customer's released requirements and the relevant component instructions for the actual joint.
Separate identification from interchangeability
Lesker notes that North American CF naming commonly refers to flange outside diameter, whereas European and Asian naming commonly refers to nominal tube bore. Its notes also distinguish fixed from rotatable CF flanges and clearance holes from tapped holes.
| Reference in the inquiry | Buyer clarification | Document to request |
|---|---|---|
| CF flange | Confirm the specified gasket, flange variant and fastening arrangement. | Released mating-interface definition and referenced hardware list. |
| KF flange | Confirm the centering-ring arrangement, specified O-ring and clamp. | Approved mating-component references and seal identification. |
| Nominal port size | Confirm the naming convention and the actual interface definition. | Controlled drawing or identified standard with the required edition. |
| Adapter between families | Define each end separately and identify the supplied items. | An end-by-end interface schedule linked to the adapter drawing. |
Treat a matching name or nominal size as a starting point for review, not a decision that two components may be joined. Ask the technical authority to compare the complete mating definitions. If a supplier proposes an alternative seal or flange arrangement, require an explicit change review instead of accepting it as an undocumented equivalent.
Use one interface schedule for each port
Assign a port identifier on the customer drawing. For each port, record the mating component reference, flange family, seal reference, fastening arrangement and customer-controlled acceptance document. Identify which items are included in the order and which will be supplied by the integrator. Repeat the exercise separately for every port on a housing.
Provide the responsible reviewer with the intended service conditions and any specified cleaning or thermal-processing constraints. Ask that reviewer to approve the seal definition and component instructions. Do not copy a catalog limit into an order as evidence that the complete custom assembly is suitable for that service.
Ask the supplier to identify any conflict between the released interface and the proposed manufacturing route. Keep the sealing feature, nearby mounting features and referenced mating geometry visible in the review package. Route any proposed alteration of the sealing feature to the customer's technical authority before releasing the change.
Define the required evidence separately for the component and any assembled joint. If leak testing is required, ask who supplies the mating hardware, which assembly is tested, which customer-approved procedure governs, and what record must accompany delivery. Do not treat a dimensional record as the answer to an unspecified leak-test requirement.
Resolve an ambiguous housing inquiry
Imagine an inquiry for a housing with a port labelled only 'KF connection' and a photograph of a neighboring assembly. Instead of guessing the seal or copying dimensions from the photograph, request the authorized interface drawing and mating-item reference. List the O-ring, centering arrangement and clamp as included, customer-supplied or unresolved.
If the drawing shows one connection family while the parts list calls out another, retain both references and open a clarification. Ask for a corrected, approved package. Do not resolve the conflict by selecting whichever attachment arrived last, and do not manufacture an adapter that was never included in the approved scope.
Interface review and quotation comparison
Compare quotations against the same port schedule. Check that every bidder identifies the same supplied component, seal and hardware boundary, and the same evidence obligations. Keep unresolved interface decisions visible alongside the quote. The useful handoff is an approved definition with named responsibilities, not an unqualified request for a vacuum flange.
Related review paths
References
- ConFlat® (CF) UHV Flanges & Components Technical Notes — Kurt J. Lesker Company. Accessed 2026-09-13T06:13:03.568Z.
- KF (QF) HV O-Rings & Centering Rings — Kurt J. Lesker Company. Accessed 2026-09-13T06:13:03.568Z.