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When zero leakage isn't just a goal — it's a requirement.
VCR stands for Vacuum Coupling Radius Seal — a metal-to-metal sealed tube fitting originally pioneered by Swagelok®. Over the decades, it has become the de facto industry standard for metal face-seal connections.
In fact, due to Swagelok's massive influence, "VCR" has become a generic term — fittings from other brands of the same design are all commonly referred to as VCR fittings.
Core Definition: VCR fittings achieve metal-to-metal high-purity sealing by interlocking male and female nuts to compress a precision metal gasket, delivering leak-tight performance from ultra-high vacuum to positive pressure.
The magic of a VCR fitting comes down to one word — PRESSURE.
When the male nut and female nut are threaded together, the flanges on both ends of the gland simultaneously squeeze the metal gasket inward. Under this compressive force, the gasket undergoes plastic deformation, conforming perfectly to the polished sealing faces on both sides — creating a zero-leak metal seal ring.
| Fitting Type | Leak Rate |
|---|---|
| Threaded Seal | 10⁻¹ ~ 10⁻² He·sccs |
| Compression / Ferrule | 10⁻³ ~ 10⁻⁵ He·sccs |
| VCR Metal Gasket | ≤ 10⁻⁶ He·sccs |
That's up to 10,000× tighter than standard threaded connections. No wonder it's called the ceiling of sealing.
A complete VCR connection consists of five core components — each one is critical:
| # | Component | Function |
|---|---|---|
| ① | Short Gland | Connects to one end of the tubing |
| ② | Long Gland | Connects to the other end of the tubing |
| ③ | Female Nut (Internal Thread) | Provides internal thread clamping force |
| ④ | Male Nut (External Thread) | Provides external thread clamping force |
| ⑤ | Metal Gasket | The heart of the seal |
⚠️GOLDEN RULE: The gasket is a single-use consumable. It MUST be replaced every time you disassemble the fitting. No exceptions.
Gasket Types:
| Type | Description |
|---|---|
| Non-Retained (Smooth) | Flat ring, placed freely between flanges |
| Retained (Clawed / Tooth-Lock) | Features retention teeth to hold gasket in place during assembly |
Common Gasket Materials:
| Material | Temperature Range | Best For |
|---|---|---|
| 316L Stainless Steel | -269°C ~ 537°C | Most general & high-purity applications |
| Nickel (Ni 200) | -269°C ~ 315°C | Cryogenic & corrosive environments |
| Copper (Cu) | -269°C ~ 315°C | Ultra-high vacuum (UHV) systems |
| Aluminum (Al) | -269°C ~ 250°C | Lightweight / low-temp applications |
| Industry | Typical Applications |
|---|---|
| Semiconductor | Ultra-high purity gas delivery, UHV process chambers |
| Biopharma | Sterile tubing, drug R&D, aseptic process lines |
| Aerospace | Specialty gases, rocket propellant transfer |
| Solar / PV | High-purity process gases in solar cell manufacturing |
| Nuclear | Safe transfer of radioactive / hazardous gases |
Bottom line: Wherever cleanliness, leak-tightness, and safety are non-negotiable — VCR is the answer.
| Feature | VCR | Compression / Ferrule |
|---|---|---|
| Seal Type | Metal gasket face seal | Dual-ferrule bite seal |
| Leak Rate | ≤ 10⁻⁶ He·sccs | 10⁻³ ~ 10⁻⁵ He·sccs |
| Welding Required? | Yes (Gland → Tube) | No |
| Cleanliness | Ultra-high (Electropolished) | High |
| Ease of Assembly | Moderate (Gasket replacement) | Easy & Fast |
| Reusability | Limited (Gasket = consumable) | Highly reusable |
| Best For | UHP / UHV / Critical process | General industrial tubing |
| # | Tip | Details |
|---|---|---|
| 1 | Size Matters | Available in Imperial (1/8" ~ 1") and Metric (6mm ~ 18mm). Always match tube OD exactly. |
| 2 | Thread Compatibility | NPT (60°) vs PT/BSP (55°) — NEVER mix them. Wrong thread = can't tighten or can't disassemble. |
| 3 | Silver-Plated Nuts | Internal thread silver plating reduces galling and ensures consistent torque over repeated assemblies. |
| 4 | Installation Rule | Place gasket → align flanges → hand-tighten → torque with wrench. Never slide flanges across the gasket — it will scratch the seal face and ruin the seal. |
| 5 | Torque Values | Follow manufacturer specs. Over-torquing = gasket extrusion; Under-torquing = leaks. |
Born in the aerospace industry, the VCR fitting has quietly become the lifeline of modern high-tech manufacturing — semiconductors, biopharma, new energy, and beyond.
It uses the simplest principle imaginable — metal pressing against metal — to deliver the most demanding performance:
Zero leaks. Ultra-clean. Zero compromise.
That's not just engineering. That's the VCR way.
Save this guide. Share it with your team. Next time someone asks "Why VCR?" — send them this article.
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