Masoneilan 28000 BS Bellows Seal Varipak Microflow Control Valve
Overview
The Masoneilan 28000 BS is the bellows seal version of the Baker Hughes Varipak microflow control valve. In the Varipak numbering system the BS suffix designates the bellows seal construction, and the technical specification lists it as the 28000 BS Series. A metal bellows seals the stem so that there is no leakage at the packing box. Baker Hughes describes the design as ideal for flammable, toxic or explosive fluids, where even the small fugitive leakage of a packing box is unacceptable.
In Oman and the GCC, Seven Star LLC proudly supplies the Masoneilan 28000 BS to oil and gas, chemical and laboratory customers across the Sultanate of Oman and the GCC. Our valve team in Muscat helps confirm the operating pressure and temperature against the bellows ratings, and whether the Viton O-rings of the construction are compatible with your fluid, before an RFQ is raised.
Operating Principle of the Bellows Seal
In a conventional Varipak the plug stem passes through a packing box, and the packing is the only barrier between the process and the plant. In the Masoneilan 28000 BS the stem is part of a bellows stem sub-assembly in solution-annealed 316L stainless steel, so the stem seal is a metal bellows that flexes with the stroke instead of a packing that rubs on the stem. The bellows construction table still lists a carbon core braided PTFE packing set, together with a packing retaining ring in 316 stainless steel and an adjustment ring in 316L, and it lists retaining screws in ISO 3506 grade A2-70 and a grooved pin in 316 stainless steel.
The trade-off of a bellows in the Masoneilan 28000 BS is a lower limit on pressure and temperature. The bellows construction page of the technical specification lists operating pressures of 55 bar (800 psi) at +100°C (+212°F) and 40 bar (580 psi) at +200°C (+392°F), within a temperature range of -29°C to +200°C (-20°F to +392°F) for the AISI 316L construction. The body rating is ASME Class 150 to 600 (ISO PN 10 to 100), and the bellows pressures above are listed separately from it. The general data table on page 4 quotes the same two bar values (54 and 40 bar) but attaches the psi figures the other way round, which does not agree with the unit conversion; this page therefore follows the construction page, where bar and psi match.
Engineering Design of the Masoneilan 28000 BS
The Masoneilan 28000 BS is offered in the 1/2, 3/4 and 1 inch sizes (DN 15, 20 and 25), with flanged, flangeless or threaded ends and a face-to-face length of 4.02 inches (102 mm) for the flangeless body. The rated Cv range is 2.3 to 0.0040, which covers trim numbers 1 to 9; trim number 0, the 3.8 Cv trim of the standard valve, is not applicable to the bellows design. Seat leakage is Class IV and flow is to open, as for all Varipak constructions. The remaining parts, such as body, seat ring, seat ring gasket and plug, are taken from the standard stainless steel material table, which lists a Grafoil gasket bonded to 316 stainless steel for the seat ring.
The bellows version of the Masoneilan 28000 BS uses two O-rings in Viton-A of 65 to 75 Shore A hardness, and Baker Hughes notes that the compatibility of these O-ring materials with the process fluid must be checked. The actuator stem is solution-annealed 316 stainless steel and the stem coupling is austenitic stainless steel. The actuator on top is the standard Varipak spring-opposed rolling diaphragm design with direct or reverse action, the optional handwheel and the optional Cv adjustment knob, so the valve keeps the compact footprint of the standard Varipak.
Key Features
The following points describe what the Masoneilan 28000 BS adds to the standard Varipak:
- A metal bellows in the Masoneilan 28000 BS gives zero leakage at the packing box for flammable, toxic and explosive fluids.
- Carbon core braided PTFE packing is still listed as a secondary seal in the bellows construction.
- Rated Cv from 2.3 down to 0.0040 through trim numbers 1 to 9.
- Bellows operating pressures of 55 bar (800 psi) at +100°C and 40 bar (580 psi) at +200°C.
- Body ratings from ASME Class 150 to 600 and ISO PN 10 to 100, in 1/2, 3/4 and 1 inch sizes.
- Bellows stem sub-assembly in solution-annealed 316L stainless steel.
- Class IV seat leakage and flow-to-open action, with the compact Varipak actuator.
- Same 5.5 inch (140 mm) removal clearance as the other Varipak constructions.
Industrial Applications
The Masoneilan 28000 BS is used wherever a stem leak is an environmental, safety or health problem and the flow is very small: sampling lines for hydrocarbon analysers, toxic gas dosing, flammable solvent metering and laboratory pilot plants. In Oman the fugitive emission requirements of gas processing plants and refineries, as well as the safety rules of chemical plants in Sohar, make a bellows seal an attractive choice for small instrument-scale valves.
Seven Star LLC supplies the Masoneilan 28000 BS as the trusted supplier for Masoneilan, serving contractors and operators in Oman and the GCC, including the Sohar and Salalah economic zones. For clean non-hazardous services the standard Masoneilan 28000 Series Varipak valve is simpler, the 28000 Varipak seal and O-ring kit covers routine spares, and a Masoneilan SVI3 digital valve positioner can be specified where the Varipak accessory list calls for digital positioning.
Technical Specifications
The table presents the bellows seal data published for the Masoneilan 28000 BS in the Baker Hughes Varipak technical specification (Rev. C, 12/2025) and the 28000 fact sheet. For complete data, consult the official documents.
| Parameter | Specification |
|---|---|
| Model | Masoneilan 28000 BS (Varipak bellows seal design) |
| Valve sizes | 1/2, 3/4 and 1 in (DN 15, 20 and 25) |
| Body rating | ASME Class 150 to 600 / ISO PN 10 to 100 |
| Rated Cv range | 2.3 to 0.0040 (trim numbers 1 to 9; trim 0 not applicable) |
| Operating pressure | 55 bar (800 psi) at +100°C (+212°F); 40 bar (580 psi) at +200°C (+392°F) |
| Temperature range | -20°F to +392°F (-29°C to +200°C) |
| Seat leakage | Class IV |
| Flow direction | Flow to open |
| Bellows stem sub-assembly | Solution-annealed 316L stainless steel |
| Packing set | Carbon core braided PTFE |
| Seat ring gasket | Grafoil bonded to 316 stainless steel (standard materials table) |
| O-rings | Viton-A, 65 to 75 Shore A (check fluid compatibility) |
| Face to face, flangeless | 4.02 in (102 mm) |
| Removal clearance | 5.5 in (140 mm) |
Related Masoneilan bellows seal valves are the Masoneilan 21000 Series globe valve with BS option and Masoneilan 78400/18400 LincolnLog valve.
Request a Quote for Masoneilan 28000 BS
Requests for the Masoneilan 28000 BS should name the fluid, flow rate, operating pressure and temperature, so that the trim number and the bellows rating can be checked before an offer is made. The Muscat instrumentation division at Seven Star LLC confirms availability and lead time and supplies the technical specification and fact sheet for download from this page. In Oman and the GCC, we supply Baker Hughes valves with manufacturer documentation and local support.
Masoneilan control valves and actuator series
The globe valve listing centers on the 21000 series, including the cryogenic version with extension bonnet, and the 41005 cage-guided series in high pressure, API 6A and VRT anti-cavitation executions. The 80385 and 80386 are three-way combining and diverting valves. Rotary products include the 35002 Camflex II and the 37002 MiniTork II butterfly control valve. Actuators cover spring-diaphragm, cylinder and rack-and-pinion designs, among them the 5A cylinder actuator for Camflex II. Masoneilan also makes pressure regulators, SVI digital valve positioners and displacer-type level instruments, and offers Lo-dB trim for noise control.Where Masoneilan valves are used
Throttling duty on steam, hydrocarbons, gas and water is the daily work of these valves: feedwater and steam conditioning in power plants, separator and compressor loops in gas processing, high pressure drop letdown, cryogenic service in LNG and air separation, and general flow, pressure and level control in refineries and chemical plants.Ordering Masoneilan valves and spare parts: what we need
For spare parts the serial number is decisive, since the factory record behind it lists trim, materials and actuator. Send a clear nameplate photo with serial number, model number, size and pressure class. For a new valve add the process data: fluid, inlet and outlet pressure, temperature, minimum, normal and maximum flow, required leakage class, fail position, air supply and control signal.Browse Masoneilan products by category: Control Valves, Valve Actuator, Regulators, Valve Positioner, Level Transmitter.
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