KF25 Vacuum Viewport — KF25 Sight Glass for High Vacuum
KF25 vacuum sight glass (ISO-KF25) for high-vacuum systems. Available in borosilicate, fused silica and sapphire. Compact, quick-install KF flange, optional AR coatings and custom sizes.
Description
KF25 Vacuum Sight Glass (KF-25 Viewport)
The KF25 vacuum sight glass (ISO-KF / NW25) is a compact flanged viewport made for high-vacuum and process-observation tasks.
First, it gives you a reliable optical window for monitoring, alignment and inspection inside vacuum chambers.
Next, it seals to a stainless-steel KF flange using vacuum-compatible methods (Viton O-rings or metal gaskets) so you get repeatable, low-leak performance.
Key benefits
- KF-25 flange compatibility — installs quickly with standard KF clamps, centering rings and O-rings.
- High-vacuum sealing — O-ring or metal gasket options deliver very low leak rates.
- Multiple window materials — choose borosilicate, fused silica (quartz) or sapphire based on wavelength and bake-out needs.
- Compact & serviceable — ideal for small chambers and frequent access; remove and reinstall without special tools.
- Custom sizes & CAD — KF16 / KF25 / KF40 / KF50 versions and CAD drawings are available on request.
Why choose the KF25 viewport?
The KF25 viewport balances compact size with reliable optical performance. Additionally, quartz and sapphire variants withstand higher bake-out temperatures and transmit UV and laser wavelengths with minimal loss.
Therefore, if you need UV transmission or high-temperature bake, choose fused silica or sapphire. Finally, our engineers will advise the best material and sealing approach when you share operating pressure, temperature and wavelength.
Typical technical specifications
| Specification | Value / Notes |
|---|---|
| Model | KF25 vacuum viewport (KF-25) |
| Rated vacuum | Leak rate to ≈1×10⁻¹² Pa·m³/s (typical with metal seal) |
| Flange material | Stainless steel 304 (316 available on request) |
| Window materials | Borosilicate / Fused silica (quartz) / Sapphire / BaF₂ / CaF₂ / ZnSe (selection by wavelength / temp) |
| Surface quality | 60/40, 50/20 or 20/10 (choose per optical spec) |
| Optical flatness | Typical 1/2 to 1/10 λ depending on material and spec |
| Visible aperture (mm) | Ø25 mm (clear aperture) |
| Heat resistance (typical) | Borosilicate: 150–230°C; Quartz/Sapphire: higher bake-out temps (see datasheet) |
| Transmittance / refractive index | Material dependent; example refractive index ~1.45–1.76 for reference |
| Outer / Inner diameter | OD: 40 mm — Visible bore: 25 mm |
| Product height | 35.5 mm (typical assembly height) |
| Glass thickness | ≈4 mm (standard; thicker on request for mechanical load) |
Note: The values above are typical. Moreover, final selection depends on your chamber bake-out temperature, optical wavelength, and mechanical loads. Therefore, please confirm requirements with our engineering team before ordering.
