Bellows Seal Valve Brochure

Bellows Seal Valve

Conval Bellows Seal Valves meet all of the rigorous requirements of MSS SP-117, ensuring bellows longevity.

Bellows seal valves are valves employed in piping systems to safeguard against leakage. When selected and installed properly, they minimize the risk of potentially harmful chemicals causing injury or illness to workers and damage to the surrounding environment.

Standard Bellows Seal Sizes

Sizes through 4”

Pressure Rating

Through ASME Class through 2500 #

Standard Forging ASME Materials

SA 105, SA 182-F22, SA 182-F91, SA 182-F92, SA 182-F316
Other materials available upon request.


Actuators – Electric, Pneumatic or Hydraulic
Locking Devices – Open, Closed or Both
Limit Switches – Single or Dual
Stem Shroud
Position Indicator
Leak-Off Port

Bellows Seal Design Features

Conval Bellows Seal Valve vs. Packed Valves

Packed valves require two seal boundaries: a 360° seal on the stem surface and a 360° seal on the stuffing box wall. The Conval bellows seal valve removes these two leak paths. Conval bellows seal valves are used when packed valves may not reliably contain light gases or hazardous system fluids. In all applications, the 6-ply Inconel®, welded bellows stem seal is more reliable than sliding stem seals.

Zero Fugitive Emissions

Every Conval bellows assembly is tested for zero leakage using a helium gas mass spectrometer before undergoing further shell and seat leakage testing. Conval’s bellows seal emits no detectable leakage, well beyond Method 21 Fugitive Emissions Test Protocol.

No Torsion of the Bellows

A robust rising, non-rotating stem system prevents destructive torsion, providing extremely long service life from the advanced bellows design.

Three Body Styles

Conval bellows seal valves are available in Y-pattern, Angle-pattern, and T-pattern body styles.

Low Operating Torque

The manual bellows seal valve is provided with a rugged bearing system and grease fitting to minimize operating torque over the life of the valve.

Double Back-up Seating

In the full open position, Conval bellows seal valves are equipped with a superior backseat, isolating a secondary stem seal from the process fluid. The graphitic stem seal is precisely loaded by Conval’s balanced axial gland and Integral Gland Wrench (IGW), providing superb sealing to back up the bellows.

Extended Seat Life

Positive shut-off is achieved over a very long operational life due to the solid cobalt-chrome seats and discs, even in high cycle and high fluid velocity services. A cobalt-free option is available for nuclear and chemical applications.

Flexibility of Design

Conval offers a double height bellows which provides the highest bellows valve flow capacity (Cv) available per pipe size. Test ports (with lantern gland) may also be specified.

Axially-loaded Packing System

The Axial design ensures tight concentricity, which eliminates side loading of the packing and minimizes wear forces on the trim components. This feature is critical for superior valve performance.

Pressure Seal Bonnet

The simple and effective pressure seal bonnet provides ready access for servicing with no welds to cut or seal rings or gaskets to replace. The body-to-bonnet joint integrity is maintained through countless thermal cycles.

Single-piece Gland

In extreme environments, the simpler the design and the fewer the parts, the better. The durable single-piece stainless steel gland contributes to the longevity of the valve.

Pressure-Actuated Backseat

The Clampseal® pressure-actuated backseat provides maximum valve integrity by ensuring a positive internal stop for the valve stem and disc assembly. The pressure actuated backseat also extends packing life by securely isolating the packing from the pressure when the valve is fully open.

Rapid In-Line Renewability

The CLAMPSEAL® Valve is much easier to renew than anything else on the market. The CLAMPSEAL® Valve line provides a modular solution to rising maintenance expenses. Low acquisition cost is not as important as low cost over the serviceable life of a valve. Maintaining a Conval valve is far easier and much less costly than replacing a competitor’s valve.

How Do Bellows Seal Valves Work?

These valves feature an accordion like bellows—i.e., the bellows cartridge component, welded to the valve stem and bonnet. During the valve stroke the bellows compress or expand along with the sliding stem’s linear motion with little to no friction.

Types of Bellows

  • Formed bellows: Conval’s standard design, formed bellows begin as flat sheet (thin wall foil) rolled into a tube and fusion-welded longitudinally forming a single layer.  Thin metal layers are combined to form multi-ply bellows.  Mechanical or hydrostatic force forms the bellows with wide-spaced rounded folds. Conval has supplied bellows with as many as 6 plies for higher pressure applications.
  • Welded bellows: Welded bellows are manufactured by welding washer-like plates of thin metal at both their inner and outer circumferences.

Types of Bellows Seal Valves

Gate valves, globe valves and ball valves may all be supplied with Bellows should the application require.

Applications of Bellows Seal Valves

These critical components are an essential part of safe fluid system operation in a broad range of industries, including the following:

  • Aerospace
  • Biotechnology
  • Chemical processing
  • Fossil power
  • Nuclear power
  • Petroleum
  • Pharmaceutical
  • Semiconductor manufacturing
  • Vacuum and ultra-high vacuum


Below we provide answers to some of the most frequently asked questions (FAQs) regarding bellows seal valves.

What are some advantages of using bellows seal valves?

The primary function of bellows seal valves is preventing potentially harmful or toxic fugitive emissions which can negatively affect unprotected humans and the surrounding environment. In addition to reducing the risk to employees or the environment, these valves decrease the amount of material lost during operations, which translates to lower overall material costs and greater throughput.

How do I choose a bellows seal valve?

When selecting a bellows seal valve for a system, there are several factors to keep in mind. Some of the key design considerations are:

  • The valve material chosen should be compatible with the operating conditions of the system, including the fluid media, temperature, and pressure. Common materials employed include stainless steel and nickel-based super alloys.
  • Pressure rating. The valve should be rated to handle the range of pressures and temperatures expected from the fluid system. Typical ratings range from ASME 150 to 2500 class.
  • Design Qualifications. Ensure the bellows is qualified to industry standards such as EPRI, MSS, API, or ISO.
  • The size of the valve should suit the design of the system. Conval bellows seal valves are available in sizes ranging from ¼ inch through 4 inch NPS.

How to prevent bellows seal valves from failing

Bellows seal valves are built for reliable operation. While rare, failures do occur. Generally, the root cause of the failure stems, not from the quality of the valve or bellows, but from improper selection, installation, or operation. Some guidelines for avoiding valve failure include:

  • Monitor for excessive back pressure or high inlet pressure variations
  • Select properly sized valves and bellows
  • Operate within the design pressure, temperature and stem stroke ranges.
  • Prevention of cavitation, flashing and other unusual damaging flow conditions.

Contact the Valve Experts at Conval, Inc. Today

For all your bellows seal valve needs, turn to the valve experts at Conval, Inc. Since our founding in 1967, we have developed a reputation as a premier manufacturer of high-pressure/temperature, forged steel valves suitable for use in the most demanding severe service applications. Our commitment to quality translates to our products’ superior durability and performance at the lowest life-cycle cost in the industry.

For additional information about our valve offerings or assistance specifying one (or hopefully many) for your application, contact us today.