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.
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Sizes through 4”
Through ASME Class through 2500 #
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
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.
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.
A robust rising, non-rotating stem system prevents destructive torsion, providing extremely long service life from the advanced bellows design.
Conval bellows seal valves are available in Y-pattern, Angle-pattern, and T-pattern body styles.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Gate valves, globe valves and ball valves may all be supplied with Bellows should the application require.
These critical components are an essential part of safe fluid system operation in a broad range of industries, including the following:
Below we provide answers to some of the most frequently asked questions (FAQs) regarding 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.
When selecting a bellows seal valve for a system, there are several factors to keep in mind. Some of the key design considerations are:
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:
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.
What are bellows valves
Bellow valves are a type of valve that use a flexible bellow element to control the flow of fluids or gases. The bellow element is typically made of metal or other durable materials and is designed to expand and contract in response to changes in pressure or temperature. This movement allows the valve to open or close, regulating the flow of the fluid or gas through the system. Bellow valves are commonly used in applications where precise control of flow is important, such as in chemical processing, pharmaceutical manufacturing, and other industrial settings. A Bellows Valve is a specially designed valve suitable for use in industries dealing with a hazardous medium where even minute leakages can be extremely critical. With the exponential growth of new industries such as the chemical and nuclear industry, there is a growing abundance of flammable, hazardous, extremely poisonous, and toxic media flowing through the pipelines. This creates a high risk of leakage, explosion, and health hazards. So, the valves used in such pipes and systems have specific stringent leakage and sealing requirements.
What is the costruction of bellows seal valves
A bellows valve is a type of industrial valve that uses a bellows element to create a hermetic seal. The construction of a bellows valve typically includes a valve body, a bonnet or cover, a stem, a handwheel or actuator, and the bellows element itself.
The bellows element is typically made of metal, such as stainless steel, and is designed to flex in response to changes in pressure or temperature. This flexibility allows the bellows element to compensate for thermal expansion and contraction, as well as pressure fluctuations, while maintaining a tight seal.
The stem of the valve connects the handwheel or actuator to the valve disc or plug, which is used to control the flow of fluid or gas through the valve body. The bonnet or cover is used to protect the internal components of the valve, including the bellows element and stem, from external damage or contamination.
Overall, the construction of a bellows valve is designed to provide reliable and precise control of fluid or gas flow while maintaining a hermetic seal to prevent leaks or contamination.
The types of bellows seal valve
Bellows seal valves are a type of industrial valve that use a flexible metal bellows to create a hermetic seal between the valve stem and the valve body. They are commonly used in applications where leakage cannot be tolerated, such as in chemical processing, pharmaceuticals, and food and beverage production.
There are several types of bellow seal valves, including:
1. Globe valves
2. Gate valves
3. Check valves
4. Ball valves
5. Butterfly valves
Each of these types of valves has its own unique design and characteristics, but they all use a bellows seal to prevent leakage and ensure reliable operation.
Advantages of Bellows Seal Globe Valve
1. The most prominent advantage of any bellows valve is the Double seal design (bellows + packing). So, even if the bellows fails, the stem packing will prevent any kind of leakage to meet the international sealing standards.
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2. It minimizes any loss of medium fluid and ensures the safety and environmental protection. This will ultimately improve the safety of the plant where is bellows valve has been installed.
3. It can act as an energy saver as it contributes to minimizing energy losses due to leakage.
4. Since the leakage is minimized, it prevents frequent maintenance of the valve. So, it leads to longer valve life.
5. Owing to longer service life, operating and maintenance cost is considerably reduced.
6. The rugged bellows seal design ensures zero leakage from the valve stem, thereby providing the maintenance-free conditions.
7. The safety of working personnel is improved with the installation of a bellows valve as emissions of inflammable, toxic, and hazardous chemicals can be minimized
The difference between common valve and bellows seal valves
Bellows globe valves and common valves are two types of valves used in industries to control the flow of fluids or gases.
The main difference between these two types of valves is that bellows globe valves have a bellows assembly that separates the fluid or gas flowing through the valve from the valve stem, whereas common valves do not have this feature.
When valves with gland packing are used such as gate valves or ball valves in the system for heated oil transfers (permeability of heated oil is about 50 times that of steam), chances of hot oil spillage are quite high and can cause loss of equipment and property. In such cases, due to its construction, the bellows valve can ensure absolutely nil leakage.
In ordinary valves, the shape of graphite packing cannot provide 100% effective sealing which is the main reason for frequent leakage of packing valve. As ordinary fillers are manufactured with graphite, if the purity of graphite is not adequate, its oil resistance would below. When heating oil being transferred is soaked in a graphite filler, certain graphite impurities get separated and flows along with it.
When a ball valve is used in the system with heated oil, if the internal PTFE is not resistant to high temperatures, it will quickly deteriorate and cause valve leakage.
The internal parts of the bellows valve are made of stainless steel, which can withstand a temperature of 425°C. Considering the life span of Bellows Seal Globe Valve, the duration of the general bellows valve is more than three years. Therefore, to maintain the reliability of output and to reduce the direct running costs, a bellow shut-off valve is preferred over ordinary seal valves in case of a system where heated oil is being transferred.
The bellows assembly is made of a series of convoluted metal plates that expand and contract with changes in pressure or temperature, allowing the valve to operate smoothly and without any leaks.
In contrast, common valves rely on a packing material, such as graphite or PTFE, to prevent leaks around the valve stem. This packing material can wear out over time, leading to leaks and increased maintenance costs.
Overall, bellows globe valves are generally considered to be more reliable and longer-lasting than common valves, especially in applications where leakage is not acceptable.
Selection Guide for Bellows
1. Choose the inner diameter of the bellows according to the diameter of the valve stem. The inner diameter of the bellows should be greater than the stem diameter of 115 mm.
2. The outer diameter of the bellows is selected according to the inner diameter of the bellows. The outer diameter and the inner diameter are related by the ratio of the outer diameter to the inner diameter. In general, the ratio of the outer diameter to the inner diameter is 113 to 115.
3. The wall thickness, number of layers, number of corrugrtions, and length of the corrugated pipe must meet the requirements of the pressure resistance, stroke, and cycle life of the corrugated pipe. Under normal circumstances, greater the pressure, more thickness of the bellows is required. To increase the displacement or reduce the stiffness of the bellows and increase life, the thickness of the single layer can be reduced and the number of layers of the bellows can be increased.
4. For handling higher pressures, the multiply design of bellows is recommended. The pressure that bellows can withstand can be increased by using 2 or 3 piles of the metal wall as in case of multiply design of bellows. Pressure rating by using a two-ply bellow can increase by 80% to 100% than single-ply bellow of the same thickness. Alternately, the stroke length is reduced if single-ply bellow of a thickness equivalent to the pressure rating of two ply bellow is used. So, we get a distinct advantage of multiply design over the single-ply thick bellows.
5. To prevent the distortion of bellows, the designed guide structure must be strictly followed.
6. To prevent wear and premature failure, local contact between the valve stem or bellows must be avoided.
7. The design should be such that twisting and torsional deformation of the bellows is prevented.
8. The valve design should be limited by the extension stroke and compression of the bellows. This is to prevent displacement of the bellows and to withstand compression and tensile extension beyond the defined cycle life test. Under normal conditions, the stroke of the bellows should not exceed 25% of the free length. If this is not fulfilled, it will affect the cycle life of the bellows, especially bellows valves under high temperature and high-pressure environment.
9. The bellows adopt the same pressure and temperature grade as the Bellow seal Globe Valve. The bellows must withstand the pressure test of the nominal pressure of the main valve at 38 ℃ and 115 times the nominal pressure at 38 ℃. During the pressure test, the weld should not crack or leak, and the bellows should not twist.
10. The material of the bellows components should be selected within the allowable temperature range, and it should have good formability, welding performance, and compatibility with the medium.
Application range of Bellows Seal Globe Valve
· Bellows valves eliminate the risk of leakage of the process fluid and are therefore ideally suited for applications where leakage cannot be tolerated from the valves. So, places where highly hazardous materials such as hydrogen, ammonia, chlorine, and other similar poisonous or explosive material are handled, these valves are preferred.
· It is suitable for use as a shut-off valve with heat-conducting oil, toxic, flammable, highly permeable, environmentally polluting, and radioactive fluid pipelines. It can be considered as a high-quality product for creating a leak-free factory.
· To name a few, bellows seal globe valve is highly used in petrochemical industries, electronics industry, various plants, vacuum industries, etc.
Precautions for Bellows Seal Globe Valve
Ø To avoid damage or injury to personnel or equipment, always read all warnings and instructions. Unprofessional re-conditioning, the use of foreign replacement parts, or the incorrect maintenance steps, may cause a loss of efficiency or lead to personnel injury or damage to parts.
Ø Use double seal bellows in case of a highly corrosive chemical environment so that you get two protective layers of sealing.
Ø If you find that there is a smell of media in the air or the valve cover is wet, it is generally because the bellows have been damaged by the medium.
Ø You can replace the bellows by yourself or get it replaced by makers. Replace it to avoid prolonged negligence, a threat to life, and damage to the entire valve.
Ø An excessively tightened gland nut can cause excessive packing wear and can hinder the free movement of the plug stem.
Reasons for Leakage of Bellow Seal Glove Valve
There are many reasons for the leakage of a Bellows Seal Valve. Bellows valve leakage is generally divided into internal leakage and external leakage.
1. It is because the liquid medium contains solid impurities that damage the sealing surface and cause failure.
2. Combined with the analysis of the on-site usage, the reason for the leakage of the valve stem is mainly related to the valve structure, working environment, and operation mode.
3. The valve stem adopts a double sealing structure of bellows and packing. The bellows are welded with the inner lining ring and the outer lining ring to form a bellows assembly and then welded with the valve stem and the guide body to block the leakage of the medium through the valve stem. The valve stem of the bellows valve moves up and down by the flat key, until the upper-end surface of the flat key contacts the lower end surface of the lower packing. Since the lower packing is made of PTFE material, if the valve is opened too much, the flat key will be embedded in the packing, the bellows valve can no longer be opened and closed, and the bellows assembly is knocked to death, causing the medium to leak along the valve stem.
4. Tensile elongation and compression of the bellows valve according to the line determination process can contribute to leakage. If tension or compression exceeds the limit, the bellows may be damaged, resulting in small series hose rupture, seal failure. Therefore, it is necessary to increase the limit device for opening and closing of the bellows valve, so that the bellows always expand and contract within the design range during the operation of the valve.
Summary
The unique design of Bellows Seal Globe Valve and its efficiency to provide leak-proof operations makes it the best-suited valve for a wide range of applications, especially hazardous materials & where system media is at high temperatures. Durability, maintenance-free operations and cost-effectiveness is an added benefit with bellows valves.
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