VENTURI / Technical insight
Bellows-Sealed Globe Valves: Operation and Selection
Quick answer
A metal bellows seals the moving stem against leakage to atmosphere. The disc-to-seat contact shuts off flow inside the line. External stem sealing and internal seat leakage are therefore separate performance requirements.
Which leakage path does the bellows address?
The bellows flexes with stem travel, forming a barrier between the fluid and the outer stem area. Some designs include backup packing. It does not remedy a bonnet-gasket or flange leak. The term “bellows-sealed” alone is not a whole-valve leakage class, emissions certificate or maintenance-free guarantee.
Which data matters for steam and hot fluids?
Specify normal and maximum pressure-temperature conditions, fluid composition, differential pressure and cycling. Distinguish saturated from superheated steam. Check body, bellows, stem, disc, seat and gaskets individually. A metal bellows does not make every model suitable for every steam temperature or chemical.
Why do cycle life and throttling duty matter?
The bellows is a moving element, so expected cycles belong in the specification. A stated cycle life is meaningful only with its stroke, pressure and temperature conditions. An isolation disc and a dedicated throttling trim serve different duties. Continuous modulation needs verification of control behaviour, actuator and bellows cycling capability.
How are flow direction and maintenance determined?
Follow the selected valve’s markings and instructions; there is no universal orientation rule for all bellows globe valves. Include external-leakage and function checks in the maintenance plan. Service requires isolation, depressurisation and a safe temperature under the plant’s authorised procedure.
Checking stock for a bellows-sealed globe valve
Send size, rating, body and bellows materials, connection, fluid, conditions and quantity to Venturi. Declare special emissions or test requirements before quotation. Stock supply options are available; the suitable model, available quantity and dispatch date are confirmed before ordering.
| Check | Information for the decision |
|---|---|
| Stem / bellows | Atmospheric leakage and cycling conditions |
| Disc / seat | Internal leakage with the valve closed |
| Body / bonnet | Pressure boundary and joint integrity |
Frequently asked questions
Does the bellows prevent seat leakage?+
No. It seals the stem area; internal leakage depends on disc and seat contact.
Is a bellows valve maintenance-free?+
Maintenance is still required; intervals depend on service and manufacturer instructions.
Is ISO 15848 the same as a seat test?+
No. ISO 15848 addresses fugitive emissions; internal seat tightness is tested separately.
Contact Venturi for selection and technical verification against your application requirements.
