In ultra-high purity gas and vacuum systems, a standard tube fitting is not always enough. Where cleanliness, leak integrity, and metal-to-metal sealing are non-negotiable, engineers reach for a metal gasket face seal fitting, widely known in the field as a VCR fitting. This article explains what these fittings are, how they seal, where they are used, and what to consider when you specify them.
One point on the name before we start. “VCR”, but in everyday engineering language it is often used as shorthand for any metal gasket face seal fitting. Throughout this article we use the generic term “metal gasket face seal fitting” for the product type, and we explain how FITOK supplies these as its FR series.
What a metal gasket face seal fitting is
A metal gasket face seal fitting creates a leak-tight, metal-to-metal seal between the two halves of a connection, using a replaceable metal gasket. It is a make-and-break connection, which means you can assemble it, take it apart during maintenance, and reassemble it with a fresh gasket. Because the seal is metal-to-metal rather than elastomeric, these fittings suit applications where an 0-ring would not survive the fluid, the temperature, or the purity requirement. They also have less internal entrapment than a typical tube fitting, which keeps the flow path cleaner and limits the places where particles or contaminants can collect.
How it works
The seal is formed by two precisely machined sealing beads, one on each side of the joint, that compress a soft metal gasket. As you tighten the male and female nuts, the beads deform the gasket, and the gasket flows into the fine surface texture of the beads to create a gas-tight seal. The gasket must always be softer than the beads, so the beads keep their finish and can be reused, while the gasket is replaced at each remake. Assembled correctly, this design delivers a leak-tight seal from high vacuum all the way through to positive pressure, which is exactly what ultra-high purity and vacuum systems demand.
Why choose them over other fittings
The main reason engineers specify a metal gasket face seal fitting is the metal-to-metal seal itself. With no elastomer in the sealing path, the fitting can handle aggressive, toxic, or high-temperature media that would degrade an 0-ring over time. Cleanliness is the second reason: the reduced entrapment and the smooth, controlled internal finish leave fewer places for particles to gather, which matters when contamination is measured in parts per billion. Third is leak integrity, since these fittings are designed for very low helium leak rates that suit the most purity-sensitive systems. Finally, they are built to be serviced. The make-and-break design lets you open the system and reseal it reliably simply by fitting a new gasket.
Key specifications to consider
Getting the specification right comes down to a handful of choices. The size is the starting point, and FITOK’s FR series covers a wide range. The gasket material follows from the application: 316L stainless steel, nickel, and copper are the common options, and the choice affects the temperature range, the media compatibility, and the achievable helium leak rate. Surface finish is the next decision, with a standard internal finish of around Ra 10 microinch (0.25 micrometer) and an electropolished option down to around Ra 5 microinch (0.13 micrometer) for ultra-high purity service. Cleaning and packaging then determines how the part arrives, and FITOK offers a standard process, a special process to ASTM G93 Level C, and an ultra-high purity process, so the fitting reaches you at the cleanliness level your system requires. Taken together, these choices decide the leak performance you can expect. As a reference point, FITOK rates its FR fittings to a maximum helium leak rate in the region of 4 x 10-11 std·cm3/s with unplated, electropolished gaskets, and around 4 x 10-9 std·cm3/s with silver-plated or copper gaskets. Always confirm the exact rating for the configuration you order.
FITOK’s face seal range
FITOK groups its face seal fittings into three series so you can match the seal type to the application. The FR series is the metal gasket, metal-to-metal option, and the direct counterpart to VCR-style connections, with features such as a test port at the nut for easy leak testing, silver-plated female threads, an electropolished option, and every gland and body marked with size, material, and heat number for traceability. The FO series is an 0-ring face seal fitting, the counterpart to VCO-style connections, for applications where an elastomer seal is acceptable. The TFO series uses a lubricant-free L-ring design with reduced internal entrapment. For ultra-high purity and semiconductor work, the FR series is usually the relevant choice.
Where they are used
Metal gasket face seal fittings are the standard for ultra-high purity gas delivery in semiconductor manufacturing, where they carry process and specialty gases to the fabrication tools. They are equally at home in analytical systems, high vacuum systems, specialty gas panels, and hydrogen applications. In short, they suit anywhere that leak integrity and cleanliness are critical and an elastomer seal is unsuitable.
Installation best practice
Assembly is straightforward, but a few habits protect the seal. Put the gland, gasket, and nuts together and tighten finger-tight, then tighten a further 1/8 turn for 316L stainless steel and nickel gaskets, or 1/4 turn for copper gaskets, while holding the body steady, following the current FITOK instructions for the exact part. Use a new gasket for every assembly and never reuse one after a joint has been broken. Avoid over-tightening, which can damage the sealing beads and cause a leak, and do not intermix face seal components from different brands, since they are engineered as a matched set.
Getting the specification right
Metal gasket face seal fittings reward careful specification: the right gasket material, the right surface finish, and the right cleaning level for your system. If you are matching fittings to an ultra-high purity or semiconductor application, we can help you select the correct FITOK FR configuration and supply it from stock.
Need help specifying face seal fittings for your system? Our engineers can guide your product selection and prepare a tailored quotation. Contact us to get started.
