Product Name
KF40 Centering Ring – SS304 Inner Ring for ISO-KF Flanges, KF16 / KF25 / KF40 / KF50 (KF-CR)
Product Summary
A KF40 centering ring in SS304 stainless steel, CNC machined, also made in KF16, KF25 and KF50. This is the inner ring of an ISO-KF quick-flange joint: it sits between two KF flanges, centers the bore and carries the seal so a KF clamp can pull the connection tight. Supplied as the bare ring, without O-ring; 316 stainless made to order.
ISO 9001 · CE · Manufacturer since 1999 · Made in Taiwan
KF40 Centering Ring in SS304, Also in KF16, KF25 and KF50
A KF40 centering ring is the inner metal ring of an ISO-KF quick-flange joint. Ours is CNC machined from SS304 stainless steel and made in four sizes: KF16, KF25, KF40 and KF50. The ring sits between two KF flanges, centers the bore so the two sides line up, and carries the elastomer seal in its groove. A KF clamp then pulls the two flanges onto the ring and the joint is vacuum tight, with no bolts, threads or welding.
The ring is supplied bare, without O-ring, so you fit the elastomer your process calls for. 316 stainless is made to order. The same ISO-KF flange is used on our KF vacuum valves (NW16 to NW50), so one ring size serves both the valve and the line it sits in.
Which KF Centering Ring Size Do You Need?
KF, NW and DN are three names for the same nominal size. A KF40 centering ring, an NW40 centering ring and a DN 40 ISO-KF centering ring are the same part. Match the ring to the nominal size stamped on your flange or valve.
| Ring | Also written | Nominal bore | Flange OD (ISO-KF) |
| KF16 centering ring | NW16, DN 16 ISO-KF | 16 mm | 30 mm |
| KF25 centering ring | NW25, DN 25 ISO-KF | 25 mm | 40 mm |
| KF40 centering ring | NW40, DN 40 ISO-KF | 40 mm | 55 mm |
| KF50 centering ring | NW50, DN 50 ISO-KF | 50 mm | 75 mm |
Flange outside diameters are the ISO-KF standard values, so the ring mates with ISO-KF flanges and clamps of the same size from any maker.
Key Specifications
| Item | Detail |
| Part | KF centering ring, inner ring only (model KF-CR) |
| Standard | ISO-KF (ISO 2861) clamped quick-release flange |
| Sizes | KF16, KF25, KF40, KF50 (NW16, NW25, NW40, NW50) |
| Material | SS304 stainless steel standard; 316 stainless made to order |
| Manufacture | CNC machined |
| Function | Centers the bore between two KF flanges and carries the seal |
| Supplied as | Bare ring, without O-ring |
Manufactured under our ISO 9001 quality system.
How a KF Centering Ring Works
ISO-KF is the small-flange standard for vacuum lines. KF stands for Kleinflansch (small flange) and NW for Nennweite; both refer to the same ISO 2861 dimensions. The two flanges in a KF joint are identical and have no bolt holes. Everything that makes the joint work sits between them: the centering ring, the seal it carries, and the clamp around the outside.
The ring does three jobs. Its stepped profile keys into each flange, so the two sides are held concentric. Its outer groove holds the elastomer seal at the right diameter. And its faces give the clamp something solid to compress the seal against. Close the clamp and the joint is made; open it and the line comes apart in seconds, which is why KF is the usual fitting on pump lines and small vacuum systems.
Applications
- Roughing and foreline plumbing between vacuum pumps and chambers.
- Vacuum system piping, valves and pump ports in the KF16 to KF50 range, from rough to high vacuum service.
- Research and teaching laboratories that build and rebuild small vacuum rigs.
- Temporary test connections for leak detectors and residual gas analysers on a KF port.
- Semiconductor facility subsystems such as exhaust and abatement lines, and freeze-dryer pump connections on KF16 ports.
Need the valve as well? See the vacuum valves range, including the pneumatic vacuum valve and the 3-way vacuum ball valve on KF NW40/NW50.
FAQ
Is a KF40 centering ring the same as an NW40 or DN 40 ISO-KF centering ring?
Yes. KF, NW and DN are different names for the same ISO-KF nominal size. KF40, NW40 and DN 40 ISO-KF all take the same ring, with a 55 mm flange outside diameter.
Which sizes are available?
KF16, KF25, KF40 and KF50, also written NW16, NW25, NW40 and NW50. State the size and quantity when you request a quote.
Does the ring come with an O-ring?
No. It is supplied as the bare stainless ring so you can fit the elastomer your process requires. Any standard ISO-KF O-ring of the same nominal size fits the groove.
What material is the ring?
SS304 stainless steel as standard. 316 stainless is made to order; tell us the size and quantity when you request a quote.
How is it made?
CNC machined from SS304 stainless steel, so the shoulder that locates in the flange bore and the groove that holds the seal are cut to size rather than pressed.
Which clamp does it need?
A standard ISO-KF clamp of the same nominal size. The ring is made to ISO-KF dimensions, so it mates with ISO-KF flanges and clamps of that size from any maker.
Does it fit your KF vacuum valves?
Yes. Our KF vacuum valves use the same ISO-KF flanges in NW16 to NW50, so the ring size that fits the valve also fits the line on either side of it.
What is the minimum order?
No minimum order quantity. We accept orders of any size, including small trial orders; tell us the sizes you need and we will quote them.
Sample Policy
We are happy to provide product samples for customers to evaluate quality or conduct testing. The process typically begins with a quotation based on the customer’s specifications.
If the pricing is acceptable, we can offer samples either free of charge or at a cost depending on the product type and availability.
Shipping fees are borne by the customer.
Order Process
After confirming the product requirements and other details with the customer, we will issue a Sales Confirmation for approval. Once confirmed, the customer is required to pay a 30% deposit to proceed with production.
When mass production is completed and the goods pass inspection, the customer must pay the remaining 70% balance before shipment is arranged.
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FAQ
A. How can I request a quote?
Please provide a detailed inquiry sheet including product specifications, materials, quantities, and any special requirements. We will offer a quotation based on your request.
B. What are your quotation terms?
Our quotations are typically based on FOB terms. However, we can also offer CFR, CIF, or other Incoterms upon request.
C. What is your Minimum Order Quantity (MOQ)?
MOQ depends on the product. We operate on a made-to-order basis, and trial orders are welcome. For smaller orders, freight is arranged and borne by the buyer.
D. What are your payment terms?
By T/T – 30% down payment upon order confirmation, and 70% balance before shipment.
E. What is your lead time?
Lead time depends on order quantity and specifications. We will confirm the exact schedule when you request a quote.
Want to know more?
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