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Brand: Swagelok
Swagelok SS-4BK-V51 Bellows-Sealed Valve, 1/4 in. Female VCR
Description
The Swagelok SS-4BK-V51 is a bellows-sealed valve for clean, leak-tight gas service. It is a 4BK model with a soft PCTFE conical stem tip, 1/4 in. female VCR face seal fittings at both ends, and special cleaning and packaging to Swagelok SC-11. Where the SS-4BG uses a metal stem tip and tube-fitting ends, this valve is built for metal-gasket face seal joints in semiconductor, vacuum, analytical and ultra-high-purity piping.
Technical specifications
| Parameter | Specification |
|---|---|
| Part number | SS-4BK-V51 |
| Description | Bellows-sealed valve, gasketed, PCTFE stem tip, straight pattern |
| Body material | 316 stainless steel |
| Bellows material | 321 stainless steel |
| Connections | 1/4 in. female VCR face seal (metal gasket) both ends, butt welded |
| Flow coefficient Cv | 0.36 |
| Stem tip / seat | PCTFE conical tip, soft seat |
| Body seal | PTFE-coated 316 SS gasket |
| Handle | Phenolic round handle |
| Pressure at 100 F | 1000 psig (68.9 bar) |
| Pressure at 200 F | 830 psig (57.1 bar), the maximum temperature rating |
| Minimum temperature | -20 F (-28 C) |
| Cleaning | Special cleaning and packaging SC-11 |
| Testing | Helium leak testing per SCS-00020 |
Built for face seal systems
VCR is Swagelok’s metal-gasket face seal fitting. Two beads on the fitting glands crush a nickel or stainless gasket, which gives a leak-tight joint that can be made and broken many times and withstands vacuum and thermal cycling. On the V51 valve the female VCR glands are butt welded to the body, so the valve can be dropped between male VCR ends. The metal gasket is not part of the valve and is ordered separately.
Combined with the bellows seal and the small internal volume of the B series, this keeps dead volume, particulate and atmospheric ingress to a minimum.
PCTFE seat and its limits
A PCTFE stem tip gives bubble-tight shutoff, but a polymer seat sets a lower temperature ceiling than a metal tip. The data page rates this valve at 1000 psig at 100 F falling to 830 psig (57.1 bar) at 200 F (93 C), and that 200 F is the maximum. The metal-tipped SS-4BG goes to 600 F instead. The catalog also notes that valves with VCR ends are processed to Swagelok Special Cleaning and Packaging SC-11, which is the reason for the cleaned designation in the description.
The bellows is 321 stainless steel and the body 316 stainless. The valve is helium leak tested per the Swagelok procedure listed in the catalog.
Selecting and ordering
In the code, SS is 316 stainless steel, 4 the 1/4 in. size, BK the bellows-sealed valve with a PCTFE conical tip and gasket seal, and V51 the female VCR butt-welded end. Other V-codes in the catalog cover male VCR and 1/2 in. sizes. Specify the gaskets, any actuator and the cleanliness level you need, and confirm that your fluid is compatible with PCTFE and with the PTFE-coated gasket.
Do not tighten VCR nuts without the correct gasket in place.
Documents and quotation
Source document: Swagelok bellows-sealed valves B series catalog MS-01-22 (EN), attached for download, which carries the tables this summary draws on. To get a quote for SS-4BK-V51, reply with the quantity and options, and we will check the code against the document first. Seven Star LLC is an independent supplier in Muscat.
Verify the model, rating and connection against your specification and the attached document before ordering. Related items: product category.
Datasheets & Documents
- Catalog Swagelok bellows-sealed valves B series catalog MS-01-22 (EN) Download
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About brand
Swagelok is the American maker of tube fittings and small-bore valves, best known for its two-ferrule compression tube fitting. Fred A. Lennon and Cullen B. Crawford founded it in Cleveland, Ohio, in July 1947 as Crawford Fitting Company to make that fitting. Lennon bought the whole business and the patent in 1948, and the company has been based in Solon, Ohio, since the mid-1960s.
Seven Star LLC is an independent supplier in Muscat. We list Swagelok tube fittings, needle, ball, check, relief and metering valves, filters, regulators and sample cylinders, and supply them for instrument tubing and analyser systems in Oman and the GCC by exact part number.
Swagelok company profile
| Established | July 1947, Cleveland, Ohio, as Crawford Fitting Company |
|---|---|
| Founders | Fred A. Lennon and Cullen B. Crawford; Lennon bought out Crawford in 1948 |
| Headquarters | Solon, Ohio, since the mid-1960s |
| Product families | Tube fittings and adapters, face seal fittings, needle, ball, plug, check, relief and diaphragm valves, filters, regulators, quick-connects, sample cylinders and hoses |
Milestones
- 1947: Fred A. Lennon and Cullen B. Crawford found Crawford Fitting Company in Cleveland in July.
- 1948: Lennon buys out Crawford.
- Mid-1960s: Headquarters move to Solon, Ohio.
Swagelok products we list
| Family | Models | Typical use |
|---|---|---|
| Tube fittings | Overview, SS-810-6 union, SS-810-3 tee, SS-810-9 elbow, SS-810-4 cross, SS-810-1-8 male connector, SS-810-7-8 female connector, SS-810-61 bulkhead, SS-12M0-6 metric union, VCR face seal | Leak-tight connections on instrument and process tubing |
| Needle and metering valves | SS-1RS4, SS-1RF4, SS-18RF6, SS-6NBS6, SS-20VS4, SS-4MG | Isolation and fine flow adjustment on instrument lines and sample systems |
| Ball and plug valves | 40G, 40GX 3-way, 60 Series, 83 Series, P4T plug | Quick quarter-turn shut-off and switching |
| Check, relief and sealed valves | SS-4C-1, CH, R3A, RL3, SS-4BK bellows, SS-DLS4 diaphragm | Backflow prevention, overpressure relief and leak-free sealing for toxic or high-purity media |
| Filters, regulators, sampling | SS-4F-2, SS-4TF-7, KPR regulator, sample cylinders, QC quick-connects | Analyser sample conditioning and gas or liquid sampling |
A Swagelok part number can be read directly. In SS-810-6, "SS" is 316 stainless steel, "810" means a 1/2 in. tube fitting (8 sixteenths of an inch, 10 series), and "-6" is a union. A suffix such as "-8" adds a 1/2 in. NPT end, and "M0" marks metric tube, as in SS-12M0-6 for 12 mm. Tube fittings must be made up the same way every time: finger-tight, then 1 1/4 turns for most sizes. A gap inspection gauge confirms the fitting has been pulled up.
Where Swagelok products are used
In Oman and the GCC, Swagelok fittings and valves are used on instrument impulse lines, analyser sample systems, hydraulic and pneumatic control tubing, chemical injection and gas sampling in oil and gas, refining, petrochemical, power and laboratory installations.
Ordering Swagelok products: what we need
Send the full Swagelok part number (for example SS-810-6 or SS-1RS4), the material, and the tube size in inches or millimetres. For valves, add the end connections and any options. For sample cylinders, add the volume, pressure rating and end configuration.
Facts checked against Swagelok company history, October 2026.
Browse Swagelok products by category: Pipes & Fittings, Regulators, Fittings & Valves.
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Frequently Asked Questions
What are the ends on SS-4BK-V51?
1/4 in. female VCR face seal fittings at both ends, butt welded to the body.
What is the seat material?
A PCTFE conical stem tip, which limits the valve to 200 F (93 C).
How is it cleaned?
Special cleaning and packaging to Swagelok SC-11 is shown on the data page.
What is its flow coefficient?
The Cv is 0.36.
Are VCR gaskets included?
No. Metal gaskets are a separate item, so confirm them when ordering.
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