What is the difference between a CF and a KF feedthrough?

A CF feedthrough uses a knife-edge stainless flange with an oxygen-free copper gasket and is bakeable to about 400 °C, so it suits high and ultra-high vacuum. A KF feedthrough seals on an elastomer O-ring and is hand-tightened with a clamping ring; it is quick to change but limited to roughly 10⁻³ mbar and 150 °C. Choose CF below 10⁻⁶ mbar or wherever the chamber is baked, and KF or ISO-K for rough and fine vacuum work where parts are swapped often.

How do I rate a feedthrough for current and voltage?

Rate on the conductor, not on the flange. A feedthrough with 1 mm pins may be limited to a few amps, while the same flange size with 4 mm studs or copper rods will carry 50 A or more. Derate for bundled conductors and for chamber temperature: a pin rated 10 A at 25 °C may carry only 6 A at 150 °C. Keep the working voltage at or below half the feedthrough's flashover rating where humidity is high, and never exceed the manufacturer's peak voltage including transients.

Can I add a port to an existing vacuum chamber?

Yes, provided the chamber wall is thick enough and the weld is made properly. A welded KF or CF port stub is the normal route for stainless chambers; aluminium chambers usually need a bolted flange with an O-ring seal instead. Ports should be kept short and at least one diameter away from a bend or another port, and every new weld must be helium leak tested before the chamber is pumped down again.

Vacuum Feedthroughs and Ports Singapore

Q: Does JWRESEARCH supply vacuum feedthroughs in Singapore?

Yes. JWRESEARCH supplies electrical, thermocouple, BNC, fluid, gas and optical feedthroughs together with KF, CF and ISO-K flanges, blank ports, centring rings, copper gaskets and viewports, delivered across Singapore with advice on flange standard, conductor rating and bakeout limits.

Published: {{NEW_ARTICLE_DATE}} | By JWRESEARCH | Category: Laboratory Equipment

Every vacuum chamber eventually needs something through its wall: power, a thermocouple signal, cooling water, gas or light. The flange that lets it through is the feedthrough — the part of a system most often specified last and regretted first, because one chosen on price returns later as an outgassing source or a leak that appears after the first bakeout.

JW RESEARCH SUPPLY supplies vacuum feedthroughs, ports and viewports to Singapore laboratories in KF, CF and ISO-K standards. This guide covers types, ratings, flange selection and the installation details that decide whether a joint holds.

Types of Feedthrough and Where They Are Used

The conductor or medium determines body material and insulation. Metal-ceramic bodies suit anything baked or taken below 10⁻⁶ mbar; epoxy-potted bodies suit rough vacuum at ambient temperature.

Type	Typical Conductors / Medium	Common Use	Vacuum Range
Power / high current	Copper studs, 2 – 8 ways, to 100 A	Heaters, sublimation sources	Rough to UHV
Instrumentation	1 mm pins, 4 – 20 ways, to 700 V	Thermocouples, gauges, sensors	Rough to UHV
Coaxial / BNC / SHV	Single or dual coax, 50 Ω	RF, mass spectrometry, residual gas analysers	Fine to UHV
Fluid / water cooling	Stainless tube, 6 – 12 mm	Chamber cooling, cold plates, jacket circuits	Rough to high vacuum
Gas inlet	1/8" to 1/4" tube, metering valve option	Backfill, process gas, leak testing, venting	Rough to UHV
Optical viewport	Fused silica, borosilicate, sapphire	Visual inspection, laser entry, pyrometry	Rough to UHV
Motion / rotary / linear	Shaft, bellows or magnetic coupling	Sample manipulation, shutter drive	Rough to UHV

Specification Reference

Parameter	Typical Value	What It Affects
Flange standard	KF 16/25/40/50, CF 16 – 100, ISO-K 63 – 250	Working pressure, bakeout temperature, interchangeability
Body material	304 / 316L stainless, ceramic (Al₂O₃)	Corrosion resistance and outgassing rate
Leak rate (helium)	< 1 × 10⁻⁹ mbar·L/s (CF), < 1 × 10⁻⁷ (KF)	Whether the joint meets the base pressure target
Max bakeout temperature	CF 400 °C, KF 150 °C, viewport 200 °C	Whether the chamber can be baked in place
Current rating per pin	3 A (1 mm pin) to 100 A (copper stud)	Heater and source wiring, cable and connector choice
Voltage rating	500 – 700 V DC typical, higher on request	Clearance to the chamber wall and cable insulation class
Conductor count	1, 2, 4, 6, 8, 10, 20	Signals per port and spare capacity for later additions
Insulation resistance	> 10⁹ Ω at 500 V DC	Leakage on high-impedance sensor circuits
Viewport glass	Fused silica, 2 – 5 mm, AR coated option	Transmission range and thermal shock resistance

Matching the Flange to the Working Pressure

The flange standard sets the practical limit more than the body does. KF uses a centring ring and an elastomer O-ring, hand-tightened with a clamp; it is cheap and adequate to about 10⁻³ mbar, covering most filtration and rotary evaporation work. CF uses a knife-edge and an oxygen-free copper gasket and is the only sensible choice below 10⁻⁶ mbar or when the chamber is baked. ISO-K sits between the two: claw clamp, O-ring, larger bores, common on load-locks.

Never reuse a CF copper gasket: it is crushed once, and reuse is the most common cause of a chamber that will not pump below 10⁻⁷ mbar after a modification.

Ratings: Read the Conductor, Not the Flange

A 25 mm flange can carry one 1 mm thermocouple pin or four 4 mm copper studs — an order of magnitude apart in current. Rate on the conductor, then derate for loaded pins and flange temperature: a pin rated 10 A at 25 °C may carry 6 A at 150 °C.

Keep working voltage at or below half the flashover rating in humid conditions. Singapore's humidity routinely exceeds 80 per cent, and condensation on a cool flange can bridge a gap that looked fine on the datasheet; specify longer creepage or a potted body.

Installation and Leak Testing

Clean the flange faces, fit a new gasket or O-ring, and tighten in a star pattern in two passes. For CF, torque to the gasket maker's figure — typically 15 to 25 N·m for a CF35. Over-torque distorts the flange; under-torque leaves a leak only a helium test will find.

Helium test every new joint before the chamber returns to service: spray around the flange under vacuum and watch for a rise. Record the reading — 10⁻⁸ mbar·L/s today and 10⁻⁶ next year means the gasket has taken a set.

Practical Notes for Singapore Laboratories

Keep stock of the fittings used on site: centring rings, clamp sets, copper gaskets and blank flanges in the two or three sizes on the chamber. A missing 25 mm centring ring can idle a system for a week. Store O-rings sealed and discard any that have hardened.

Where a chamber is opened often, use KF on ports accessed weekly and CF on permanent high-vacuum joints. That cuts gasket consumption and shortens pump-down.

Frequently Asked Questions

Can a feedthrough be welded into the chamber wall instead of flanged?
Yes; welded CF stubs are common on stainless chambers. The weld must be full penetration and cleaned; a welded port cannot be replaced without cutting, so leave a flanged spare port on any chamber you may modify.

Why does my thermocouple read low after fitting a new feedthrough?
Usually a wrong pin pair or the wrong compensating cable alloy. A feedthrough does not change the thermocouple type, but K-type pins with J-type extension cable add an offset that grows with temperature.

How many spare ports should a new chamber have?
At least two, preferably one of each flange size already on the chamber. Ports are cheap at build time and expensive to add once the chamber is in daily use.

Does JWRESEARCH supply vacuum feedthroughs in Singapore?
Yes — electrical, thermocouple, BNC, fluid, gas and optical feedthroughs, plus KF, CF and ISO-K flanges, blank ports, gaskets and viewports, delivered across Singapore.

Contact JWRESEARCH

JW RESEARCH SUPPLY — laboratory equipment and consumables, Singapore.
Tel / WhatsApp: +65 8039 3660
Email: SINGAPORE@JWSHY.COM
Website: www.jwresearch.cn