Bellows Sealed Gate Valve

A bellows sealed gate valve is a multi-turn isolation valve in which a welded metal bellows encloses the stem and carries the pressure boundary, so no packing is asked to seal against a sliding surface. The body is a standard gate valve body rated by ASME class, and the closure is a wedge that seats on two face rings. API 602 and ISO 15761 both cover the construction up to DN 100; above that size the body follows API 600 and the bellows bonnet becomes a drawing-level design rather than a referenced clause. The range runs DN 15 to DN 400 in Class 150, 300 and 600.

Specifications

The table covers the standard forged carbon steel build to A105N, the configuration API 602 addresses below DN 100. Above DN 100 the body keeps API 600 dimensions and adds a bellows bonnet, approved on the drawing because travel and stack height change with stem diameter.

Materials

Two lines in this table are bought differently from a standard gate valve: the bellows and its two welds. Everything else is the same bill as an API 602 body, which is why a bellows valve can be repaired with a standard trim set and a new bellows stack.

Design Standard

design features

1.Exclusively designed bellows sealed globe valve has a sealing combination featured by using double walls stainless steel bellows as the stem seal elements and graphite packing as seal accessory to prevent leakage.
2. Being the key component, double wall bellows sealing keeps the valve free from leakage and maintenance.
3. The finely polished conical sealing between the valve and the seat ensures a long-term reliable operation.

Bellows Sealed Gate Valve drawing

Dimension & Weight

CLASS 150

CLASS 300

Pressure-Temperature Ratings

A Class 150 carbon steel body holds 19.6 bar at ambient and 5.5 bar at 425 °C, a drop of 72% on the same casting. Class 600 with the same body holds 102.1 bar cold and 57.5 bar at 425 °C. The figures below are the allowable working pressure in bar gauge from ASME B16.34 Table 2, Group 1.1, which covers A105N and A216 WCB bodies.

ASME B16.34 tabulates Group 1.1 carbon steel to 538 °C, with note (1) warning that the carbide phase may convert to graphite above 425 °C. The rating stays permissible; it stops being recommended. On a bellows valve the 425 °C line matters twice - it is the carbon steel body limit and close to the practical ceiling of a 316L bellows. Above it the body moves to A182 F22 and the bellows to Inconel 625.

Actuation and Accessories

A gate valve is multi-turn, so the operator is matched on thrust and on the ISO 5210 attachment, not on the ISO 5211 pad used by quarter-turn valves. Gearboxes are the usual choice above DN 100, where the handwheel force for a Class 300 wedge exceeds what one operator should apply.

Three accessories change delivery more than price suggests: a position transmitter needs the stem cover machined for it, a chainwheel changes the yoke height, and an extended bonnet changes the total height on the same drawing.

Comparison with Other Isolation Valves

The bellows gate is chosen when both a tight closure and a sealed stem are needed on a clean fluid. It is not the cheapest way to isolate water, and it is not a control valve. The table sets it against the three types it is usually bid against.

The line that decides most enquiries is the stroke count. A DN 300 gate needs dozens of handwheel turns against a quarter-turn ball, so where the valve is cycled daily the bellows pays for its fatigue life rather than its seal.

Applications

Six services account for most of the volume on this construction. Each one is named by the property that forces the bellows, not by an industry label.

Steam header isolation at Class 300 and 600, where a packed stem would lose steam continuously and the bellows keeps the stem emission at an ISO 15848-1 class.

Thermal oil circuits, where the medium is both hot and expensive, and a gland weep is a fire risk as well as a loss.

Ammonia and LPG transfer with an A350 LF2 body, where the release is toxic or flammable and −46 °C rules out a carbon steel body.

Dry chlorine and hypochlorite, where the C-276 bellows and PTFE packing are chosen for the medium and the 316L body is not enough.

Hydrogen service, where the small molecule finds any dynamic packing and the bellows removes the sliding joint entirely.

Vacuum distillation and condenser duty, where the sealed stem stops air ingress and the PTFE packing holds the blank-off.

Each of these is a clean or lightly contaminated fluid. A slurry line, spalling scale, or a valve used as a control damper is a different product, and the enquiry should say so early.

Test and inspection

Send the line size, the class and the quantity

FAQ

What sizes and classes does a bellows sealed gate valve cover?

DN 15 to DN 400 in ASME Class 150, 300 and 600. API 602 and ISO 15761 govern the design up to DN 100; above that the body follows API 600 and the bellows bonnet is a maker-specific design approved on the drawing.

Is a bellows sealed gate valve absolutely leak free to atmosphere?

No valve is absolute. The bellows removes the dynamic stem leak path, but two welded joints, the bonnet gasket and the secondary packing remain, so tightness is declared as an ISO 15848-1 class, normally Class B or Class C.

Why keep the secondary packing if the bellows already seals the stem?

It is a failure buffer, not a duplicate. If a bellows weld or convolution fails, the graphite packing holds the joint until the next shutdown, and it is the layer that a helium test or an ISO 15848-1 cycle test can check independently.

What sets the temperature limit of a bellows sealed gate valve?

The bellows alloy and the packing, not the body. A carbon steel body is tabulated to 538 °C in ASME B16.34, but note (1) warns of graphite conversion above 425 °C, so 425 °C is the working ceiling for the standard carbon steel build.

Can a bellows sealed gate valve be used in vacuum service?

Yes. With no sliding stem seal there is no path for air to bleed into the line, provided the bonnet gasket and the bellows welds are helium tested and the body is rated for the external pressure case.

How is a bellows failure detected before it becomes a release?

Through a tell-tale port under the bonnet flange, or between the plies of a two-ply bellows. Leakage from a failed inner ply leaves through that port instead of the stem, which converts an unplanned release into a scheduled bellows change.

What documents are supplied with the valve?

An EN 10204 3.1 mill certificate, a helium test record for both bellows welds, an inspection and test plan, a general arrangement drawing and an installation and maintenance manual. An ISO 15848-1 test report and a NACE MR0175 compliance statement are added when the order calls for them.

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