Swagelok SS-4BK Bellows-Sealed Valve, B Series

Bellows-sealed shutoff valve with a soft PCTFE seat

The Swagelok SS-4BK is a manual bellows-sealed valve from the B series, made of 316 stainless steel with 1/4 in. Swagelok tube fitting ends and a conical PCTFE stem tip for soft-seat shutoff. A precision-formed 321 stainless steel bellows seals the stem to atmosphere, so there is no packing to leak, which makes the valve a fit for toxic, flammable, high-purity or expensive gases, vacuum lines and analyzer sample systems where external leakage must be controlled.

The BK designation means a gasketed body-to-bellows seal and a PCTFE tip, and the catalog processes all BK valves to the Swagelok SC-11 special cleaning standard. The actuator couples to the stem for positive retraction, and an actuator backstop is intended to protect the bellows.

Technical specifications

Data come from the Swagelok catalog Bellows-Sealed Valves, B Series (MS-01-22) and the Swagelok product page for SS-4BK.

B series variants

Other models share the platform with different seals, stem tips and sizes. Flow coefficients rise with body size, and the catalog lists the series shown below.

Options and selection notes

Choose a welded-seal BW valve when temperature goes beyond what the PCTFE tip and gasket can take: the catalog rates 316 stainless steel BW valves to 900 F (482 C) at 200 psig. For soft-seat shutoff at up to 400 F or where PCTFE is incompatible, polyimide (-VP) or copper (-CU) stem tips are offered on BG and BK valves, and vacuum stem tip adapters (-VA on BK) reduce trapped volume. Colored toggle handles are available for the 4BKT. Pneumatic actuators of 1 series and 5 series fit the B series, including normally closed, normally open and double-acting types. For a comparison with the H series, see the Swagelok SS-4H bellows-sealed valve.

How the Swagelok SS-4BK works

The SS-4BK is a stem-driven shutoff valve with a metal bellows. The handle turns the stem, which lifts or lowers a conical PCTFE tip against the seat. The bellows is welded to the stem and to the body bonnet, so it forms a flexible, sealed wall between the process fluid and the outside. The stem does not pass through any packing. That removes the usual leak path of a packed valve. A gasket seals the body to the bellows, and the soft tip gives tight shutoff.

Where the Swagelok SS-4BK is used

• Toxic and flammable gas lines
• High purity gas systems
• Vacuum lines
• Analyser sample systems
• Lines with costly process fluid

Selection checklist for the Swagelok SS-4BK

• 1/4 in. Swagelok tube fitting ends
• Working pressure of 1000 psig at room temperature
• Temperature from minus 28 to 93 degrees C
• Flow coefficient Cv 0.36
• Orifice of 0.16 in.
• PCTFE tip and gasketed seal
• Manual handle or actuator
• Panel or bottom mounting

Installation, commissioning and maintenance notes for the SS-4BK

Fit tube into the Swagelok end connections and tighten as the fitting instructions say. Mount the valve on a panel through the 0.76 in. hole if wanted. Turn the handle by hand only. With an actuator, use the backstop that protects the bellows. Leak test the joints at working pressure, and keep the valve closed or open fully, not partly, for long periods.

Requesting a quotation for the Swagelok SS-4BK

Please send the fluid, the pressure, the temperature, the end connections and the quantity. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

SS-4BK pressure and temperature

The rating is 1000 psig (68.9 bar) from minus 28 to 37 degrees C. It falls to 830 psig (57.1 bar) at 93 degrees C.

SS-4BK materials

The body and bonnet are 316 stainless steel. The bellows is 321 stainless steel. The gasket is PTFE-coated 316 stainless steel.

SS-4BK leak test and cleaning

The leak test is with helium for 5 s, at most 4 times 10 to the minus 9 std cm3/s. All BK valves get SC-11 special cleaning.

SS-4BK variants

The SS-4BG has a metal spherical stem tip. The SS-4BW has a welded body-to-bellows seal.

Valve records for the SS-4BK

Note the cycle count and the leak test results for each valve in the system.

Choosing the right SS-4BK option

Choose the tip and seal type from the temperature and the leak tightness the system needs.

Documents and quotation

The attached catalog carries the flow curves, material tables, dimensions, actuator data and kits. Before ordering, confirm the fluid, working pressure and temperature, the stem tip material, the end connection and whether a pneumatic actuator is needed. Send the ordering number and quantity for a quotation; related valves are listed under Globe Valves.