- What are the features of a bellow seal valve?
- Why bellow sealed valves?
- How to install a bellow seal valve?
- How bellow seal valves are constructed and what is a bellow?
- What is a bellow?
- How does a bellow seal valve operate and what are the types of bellow?
- Construction of Bellows Seal Valves
- Types of bellows
- Difference between a forged bellow and a welded bellow
- Selection Guide for Bellows
- Differences Between Common Valves and Bellows Seal Valves
- How is a bellow sealed valve different from piston valves and conventional valves?
- What are the advantages of a bellow seal valve?
- Types of Bellows Seal Valves
- What are the applications of a bellow seal vales?
- Reasons for Leakage in Bellows Seal Valves
- What is a bellows seal?
- Why are bellows important?
- What is the difference between pusher and bellows seals?
- What are bellows valves used for?
A bellow seal valve is a control valve that doesn’t have a conventional gland packing and instead of that these valves have a bellow cartridge and this would be welded to the valve’s bonnet and stem. The bellow can be compared to a coiled spring because it can be flexed in compression or in extension. The bellow seal valve is similar to a globe valve and their only difference is that in a globe valve we can see a gland packing along the stem but in a bellow seal valve, bellows are used to prevent the leakage instead of the packing. These valves are totally leakproof and can handle corrosive liquids. We can see these types of valves in the butadiene extraction unit.
What are the features of a bellow seal valve?
- These valves can handle high temperature and pressure
- The bellow seal can prevent the leakage of sensitive media which could be flammable
- Long life
- It can handle a good amount of steam pressure
Why bellow sealed valves?
Most of the control valves are used for flow and pressure control of process fluid. So the chances of leakage are very high and because of the leakage, there could be loss of material. The material could be radioactive or some kind of chemical and it could lead to many problems in a plant. The fluid which is used could be corrosive, explosive, or poisonous. So in order to solve this problem we can use a bellow seal valve.
How to install a bellow seal valve?
We can install a bellow sealed valve in any position, but it should not be installed in a way that the stem is upside down. So we install a bellow seal valve by considering this then we can prevent the accumulation of debris in the bellows area. So before the installation of the bellow valves, we must make sure that the pipes and valves are free from impurities. The pipes must be connected in a way that there won’t be any undue tension acts on to the housing of the valve.
How bellow seal valves are constructed and what is a bellow?
The valve body material must be selected according to the pressure, temperature, corrosive, and erosive property of the flow media. The cartridge of the bellow will be welded, there are many convolutions in a bellow cartridge and these convolutions could be compressed or expanded according to the valve stem movement. The material that is used for the construction of the bellow would be stainless steel and it would also have titanium added to it which would allow the bellow to withstand high temperatures.
What is a bellow?
A bellow can be considered as a device that is used to transmit axial motion, the bellow is a continuous convoluted tube that can sustain external or internal pressure. The bellow can be sealed to the valve in two different ways, the bellow can be welded to the valve stem at the top and the valve body at the bottom. So in this type, the process fluid will be inside the bellow. The bellow can also be welded to the valve stem at the bottom and the body on the top and in this type, the process fluid will be between the valve bonnet and the bellow.
How does a bellow seal valve operate and what are the types of bellow?
The bellow would contract and expand when the valve stem moves up and down, the bellow would get compressed if the valve is in open condition and it will be expanded if the valve is in closed condition. So the bellow is in closed packed with the stem so there won’t be any chance of leakage.
Construction of Bellows Seal Valves
A bellows valve is a specialized industrial valve that uses a bellows element to create a hermetic seal, ensuring minimal leakage and maintaining system integrity. The main components of a bellows seal valve include:
- Valve Body: The primary structure that houses the flow path for the fluid or gas.
- Bonnet or Cover: Protects internal components and connects to the valve body.
- Stem: Links the actuator or handwheel to the valve disc or plug, enabling control over fluid or gas flow.
- Handwheel or Actuator: Provides the mechanical force to operate the valve.
- Bellows Element: Made of materials like stainless steel, it flexes to accommodate pressure and temperature variations while maintaining a tight seal.
The bellows element ensures compensation for thermal expansion, contraction, and pressure fluctuations. The design of these valves prioritizes reliable and precise control of fluids or gases with a focus on leak prevention.
Types of bellows
Forged bellow
This type of bellows is constructed by rolling a flat sheet into a tube, mostly it would be a thin wall foil. This tube will be then welded longitudinally, this tube will be mechanically or hydrostatically formed into a bellow with rounded and widely spaced folds.
Welded bellow
These bellows are made by welding washer-like plates of thin metal together at both the inner and the outer circumference of the washers like plates. A welded type bellow has more folds per unit length when compared to the forged bellows. The welded bellows are shorter in length.
Difference between a forged bellow and a welded bellow
Durability
The forged bellow has good durability because these bellows are constructed from a single piece of metal and because of this the forged bellow would have good cycle life. In the case of the welded bellows, the reliability will be low because this type of bellow has small welded spots, because of this heat would be affected to this bellow, and thus its cycle life will be less.
Usage in valve
The forged bellow would have a wide opening between piles of bellows, due to this the bellow function won’t be affected by bits of foreign matter in the fluid. In the case of a wedged type bellow, the opening between piles will trap the foreign material in the fluid, and eventually, this would lead to the failure of the bellow.
Quality control
The forged type of bellow is really easy to test for quality because the forged bellows are constructed uniformly. In the case of welded bellows, it is very difficult to inspect the welded spots for quality and because of this, quality control will be really difficult.
Selection Guide for Bellows
Match bellows material to the valve’s pressure and temperature ratings.
Choose the inner diameter based on valve stem size (inner diameter > stem diameter by ~15 mm).
Select the outer diameter in proportion to the inner diameter (outer/inner ratio: 1.13–1.15).
Determine wall thickness, number of layers, corrugations, and length based on pressure, stroke, and lifecycle requirements.
Use multi-ply designs for higher pressure handling.
Ensure the guide structure prevents distortion.
Avoid local contact and excessive wear between the valve stem and bellows.
Prevent twisting and torsional deformation of the bellows.
Limit the stroke length to 25% of the free length to maintain lifecycle performance.
Differences Between Common Valves and Bellows Seal Valves
The below table summarizing the technical and operational distinctions between common valves and bellows seal valves:
| Aspect | Bellows Seal Valves | Common Valves |
| Sealing Mechanism | Metal bellows assembly separates fluid/gas from the stem, eliminating leakage. | Packing materials (e.g., graphite or PTFE) that may degrade over time. |
| Leakage Resistance | Virtually eliminates leakage. | May experience leakage over time due to packing degradation. |
| Temperature Resistance | High resistance, up to 425°C. | Limited by the material properties of the packing. |
| Suitability | Ideal for hazardous or high-temperature fluids. | Suitable for general-purpose applications with less stringent requirements. |
| Lifespan | Longer due to durable bellows design. | Shorter, as packing materials require regular replacement. |
| Maintenance Needs | Low, as bellows are durable and maintenance-free for long periods. | Higher, requiring periodic replacement of packing materials. |
| Cost | Higher initial cost due to complex construction. | Lower initial cost, but may incur higher maintenance costs over time. |
How is a bellow sealed valve different from piston valves and conventional valves?
Primary stem seal
The bellow seal valves have metallic bellow, the piston valves have piston rings and the conventional valves have gland packing.
Stem leakage
The bellow seal valve has no stem leakage, while in a piston valve stem leakage could occur when the rings wear out. In the case of the conventional valve, stem leakage is very common because of the friction between the stem and the gland.
Packing replacement and replacement cost
In the bellow seal type replacement can’t be done, while in the piston valves the rings need to be changed frequently. In the case of the conventional valve, packing needs to be replaced frequently too. The replacing costs of the piston and the conventional valve are very high.
Media loss
There won’t be any media loss in the bellow type, while in the case of the conventional and the piston valves there could be large media loss.
Valve life
The bellow seal valves has good life while the piston and conventional type only has very low life.
Safety
The bellow valves are very safe and any media can be used, while the piston valves can only be used for limited media like hot water and steam. The conventional valve is really unsafe if the media is hazardous.
Cost
The initial cost of the bellow seal valve is very high but after that, there will be only less maintenance. The piston valve cost is high when considering its benefits, while the conventional valve cost is initially very low but its maintenance cost is very high after some years.
What are the advantages of a bellow seal valve?
- Double Seal Design Combines bellows and packing for enhanced safety, meeting international sealing standards.
- Prevents fluid loss, ensuring a safer and cleaner operational environment.
- Minimizes energy loss due to leaks.
- Lowers maintenance needs and extends valve lifespan.
- Long service life reduces operational and maintenance costs.
- Rugged bellows design ensures maintenance-free operation with no leakage.
- Reduces exposure to hazardous chemicals.
- There won’t be any steam loss, and there won’t be any media loss
- Monitoring costs of this valve is very low
- It can be used for applications where leakage should be zero
- Safe and clean operation can be achieved
Types of Bellows Seal Valves
Bellows seal valves are versatile and come in several types:
- Globe Valves
- Gate Valves
- Check Valves
- Ball Valves
- Butterfly Valves
All these types share the use of a bellows seal valves to ensure leak-free operation and long-term reliability.
What are the applications of a bellow seal vales?
- Heat transfer media
- It can handle highly hazardous fluids
- Vacuum and high ultra-vacuum
- It can be used in nuclear power plant and also with heavy water plant
- These valves are used for costly fluid applications
Reasons for Leakage in Bellows Seal Valves
Improper Maintenance: Neglecting proper limits for stroke length and compression can cause failure.
Impurities: Solid particles in the medium can damage sealing surfaces.
Structural Issues: Valve design and operation may contribute to leaks.
Excessive Force: Over-tightening or over-extension of the bellows can lead to damage.
Bellows Seal Valves FAQ
What is a bellows seal?
Bellows seals are specialized industrial components featuring a flexible metal bellows that create a hermetic seal between the valve stem and the valve body. These seals are widely used in applications where leakage is unacceptable, such as in chemical processing, pharmaceutical manufacturing, and food and beverage production.
Why are bellows important?
Rubber bellows play a vital role in industrial applications as protective covers for components like shafts and rods. They provide flexibility to absorb noise, accommodate thermal movements, compensate for misalignments, and shield against dust and moisture.
What is the difference between pusher and bellows seals?
| Type of Seal | Description |
| Pusher Seals | Designed for high-pressure environments. May experience wear due to the movement of the elastomer under the primary seal face along the shaft or sleeve. |
| Bellows Seals | Non-pusher design using metal or elastomeric bellows.Maintains seal closing forces with improved durability and performance in specific conditions. |
What are bellows valves used for?
Bellows valves are critical for piping systems that transport hazardous liquids and gases. They are designed to minimize the risk of leakage, ensuring safety by preventing exposure to potentially harmful substances in chemical and industrial processes.
Refer the below useful links related to control valves
What is an automatic recirculating valve and where is it used?
What is a deluge valve and what is the need for a deluge system?
What is a counterbalance valve?
What is an anti-surge valve and what are their functions?
Refer the below link for the Valves: Resource for Professionals in the Process Industry
Refer the below link for the Control Valves in Process Industries: A Collection of In-Depth Articles
