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V-type regulating ball valve

July 1, 2021

Working principle of pneumatic V-type regulating ball valve
The ball core of the pneumatic V-shaped regulating ball valve is designed with a special V-shaped notch, which has a shearing effect on the valve seat. It is especially suitable for media containing fibers, small solid particles, slurry and other media. According to different structural methods, it can generally be divided into flange and Wafer type; Pneumatic V-type ball valve is a fixed ball valve and also a single-seat sealed ball valve. It has the best adjustment performance among ball valves and can achieve flow adjustment. At the same time, since the valve core and seat are rotated without gaps, they can be wiped by themselves. The fouling on the ball and valve seat keeps a good seal between the ball and the valve seat.

electric V type ball valve

Working principle of pneumatic V-shaped regulating ball valve:
Pneumatic V-shaped regulating ball valve realizes different degrees of proportionality according to the V-shaped angle of the V-shaped sphere. It is generally used in conjunction with a valve positioner to achieve proportional adjustment. The V-shaped spool is most suitable for various adjustment occasions and has a large rated flow coefficient. ,, The pressure loss is small, the use flow capacity is large, and it has accurate shut-off characteristics and control functions. The flow characteristics are approximately equal percentages. The opening and closing parts adopt the V-shaped ball structure, which completely solves the problem of easy deposition of medium in the valve cavity.
Features of pneumatic V-shaped regulating ball valve:
1. Pneumatic V-shaped ball valve V-shaped gap and valve seat produce a strong shear force to cut off impurities such as fibers, and has a self-cleaning function to avoid valve jamming.
2. The pneumatic V-type regulating ball valve has an inherent flow characteristic of approximately equal percentage and an adjustable ratio of up to 300:1, so it can provide precise control in a wide range of changes.

Note: Because the pneumatic V-type regulating ball valve is generally a single-seat sealed ball valve, it is not suitable for two-way use. Due to its streamlined shape and full right-angle rotation control, the maximum volume is extremely high, the flow capacity is particularly large, and the flow resistance is small.

pneumatic V type ball valve

Pneumatic V-type regulating ball valve principle dynamic diagram
The valve core of the pneumatic V-shaped regulating ball valve is designed as a V-shaped gap with a special switch. The V-shaped gap and the valve seat generate a strong shear force, which can cut off high-viscosity media containing fibers or small solid particles, and has a self-cleaning function , To avoid the phenomenon of valve jamming. Pneumatic V-shaped ball valve is suitable for regulation and control, with high stability. Even in the case of small flow or high-viscosity medium, it can also ensure the accuracy of control within the entire range; while O-shaped ball valve is suitable for cutting off, relatively It is economical.
There is a V-shaped opening on the sphere of the pneumatic V-shaped regulating ball valve. As the ball rotates, the opening area changes, but the shape of the opening surface is always triangular. The flow characteristics are approximately equal percentages, the adjustable ratio is large, and the pressure loss is small. The flow capacity is large, and it has accurate interception characteristics and control functions. The opening and closing parts adopt a V-shaped spherical structure, which completely solves the problem of easy deposition of medium in the valve cavity. It is suitable for fibrous and slurry fluids!
The angle of the V-shaped port of the pneumatic V-shaped ball valve can be customized to meet more precise shut-off characteristics and control functions. Generally, more V-shaped valves are used in slurry media. They are similar to cam flex valves and are much better than O-shaped valves. V-shaped ball valves are used as regulating valves. For example, if the medium is not clean, the flow coefficient is low, and the leakage level is high, etc. occasion.

Working principle of electric V-type regulating ball valve

V type ball valve drawing

The electric V-shaped regulating ball valve has a special-shaped V-shaped incision. When the valve is closed, the V-shaped incision and the valve seat form a wedge shape, which has a shearing effect. The electric V-shaped ball valve is suitable for the control of fibrous slurry, sewage and viscous particle media. It can prevent the seizure of dirt between the ball and the valve seat. It has a self-cleaning function and is a wide-ranging regulating valve.
When the electric V-shaped ball valve rotates, the V-shaped blade of the ball is tangent to the valve seat, thereby cutting off the fiber and solid matter in the fluid. However, the general ball valve does not have this function, so it is easy to cause the fiber impurities to get stuck when closed. , Bring great inconvenience to repair and maintenance. The valve core of the electric V-shaped ball valve will not be jammed by the fiber, and the flow rate of the pipeline medium is adjusted and controlled according to the change of the opening area of the V-shaped gap.
Note: Since the electric V-type regulating ball valve is generally a single-seat sealing ball valve, it is not suitable for two-way use. The integral valve body structure is adopted, and there is no potential for leakage.
Features of electric V-shaped ball valve:
1. It has the advantages of compact structure, small volume, vertical and horizontal installation, etc., adopts movable metal valve seat, self-compensation function, and has superior sealing performance and long service life.
2. The electric V-shaped ball valve adopts a double-bearing structure, which has high mechanical stability and low starting torque, which ensures that the valve has excellent sensitivity and induction speed.
3. Maximum reliability (safety): The valve body is a whole, sturdy and durable, operation is not affected by pipeline pressure, and leakage of the valve body can be avoided.
4. The V-shaped gap and valve seat of the electric V-shaped regulating ball valve produce a strong shearing force to cut off impurities such as fibers, and has a self-cleaning function to avoid valve jamming.
5. Maximum flow volume: Due to the streamlined shape of the electric V-shaped ball valve and the full right-angle rotation control, the maximum volume is particularly high, the flow capacity is particularly large, and the flow resistance is small.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

Properties of Fixed ball valve

May 31, 2021

The fixed ball valve is a new generation of high-performance ball valve, suitable for long-distance pipelines and general industrial pipelines. Its strength, safety, and harsh environment resistance have been specially considered in the design, and it is suitable for various corrosive and non-corrosive media. . Compared with the floating ball valve, when working, the force generated by the fluid pressure in front of the valve on the ball is all transmitted to the bearing, and the ball will not move to the valve seat, so the valve seat will not bear excessive pressure, so the fixed ball valve The torque is small, the deformation of the valve seat is small, the sealing performance is stable, and the service life is long. It is suitable for high pressure and large diameter occasions. The fixed ball valve has two-piece and three-piece valve body structures. The middle flange is connected by bolts, and the seal adopts reinforced PTFE embedded in the stainless steel ring. The rear of the steel ring is equipped with a spring to ensure that the valve seat is tightly attached to the ball. Keep it sealed.

fixed ball valve

The fixed ball valve is a new generation of high-performance ball valve, suitable for long-distance pipelines and general industrial pipelines. Its strength, safety, and harsh environment resistance have been specially considered in the design, and it is suitable for various corrosive and non-corrosive media. . Compared with the floating ball valve, when working, the force generated by the fluid pressure in front of the valve on the ball is all transmitted to the bearing, and the ball will not move to the valve seat, so the valve seat will not bear excessive pressure, so the fixed ball valve The torque is small, the deformation of the valve seat is small, the sealing performance is stable, and the service life is long. It is suitable for high pressure and large diameter occasions. The advanced spring pre-valve seat assembly has self-tightening characteristics to achieve upstream sealing. Each valve has two valve seats, which can be sealed in each direction, so the installation has no flow direction restriction and is two-way. This valve is generally installed horizontally.

The fixed ball valve has two-piece and three-piece valve body structures. The middle flange is connected by bolts, and the seal adopts reinforced PTFE embedded in the stainless steel ring. The rear of the steel ring is equipped with a spring to ensure that the valve seat is tightly attached to the ball. Keep it sealed. Both the upper and lower valve stems are equipped with PTFE bearings to reduce friction and save labor. The bottom of the small shaft is equipped with an adjustment plate to ensure the joint position of the ball and the sealing ring. Full bore diameter: The flow aperture of the valve is the same as the inner diameter of the pipeline to facilitate the pipeline cleaning.

Product features of fixed ball valve:

Operational reliability

The relative linkage (seat and stem bearing) of the large-diameter ball valve adopts Teflon with a small friction coefficient, so the operating torque is small. In addition, the long-term lubrication of the sealing grease makes the operation more flexible.

Valve seat structure

There are two types of valve seat structures: single-seal and double-seal structures. Generally, the one with self-relief function is single-seal, and double-seal is the additional safety relief on the valve body.

Lengthened stem

The extension of the valve stem is suitable for buried and low-temperature use. The length of the extension is determined according to the needs. The operation modes include manual, pneumatic, electric, gas-liquid linkage, etc.

Security of external forces

The wall thickness of the valve body is designed in accordance with the safety regulations of the high-pressure vessel, and meets the requirements of API6D for withstanding external force and bending resistance, and has sufficient strength.

As shown in the figure, the sealing of the gland part adopts four O-rings and a sealing grease injection device.

Performance advantages of fixed ball valves

Labor-saving operation: The ball is supported by the upper and lower bearings to reduce friction and eliminate the excessive torque caused by the huge sealing load formed by the imported pressure pushing the ball and the sealing seat.
Reliable sealing performance: PTFE material sealing ring is embedded in the stainless steel valve seat, and the end of the metal valve seat is equipped with a spring to ensure sufficient pre-tightening force of the sealing ring. When the sealing surface of the valve wears during use, it will be under the action of the spring. The valve continues to ensure good sealing performance.
Fireproof structure: In order to prevent the PTFE seal ring from being burnt due to sudden heat or fire, and large leakage occurs, which encourages the fire, a fireproof seal ring is set between the ball and the valve seat. When the seal ring is burned, Under the action of the spring force, the valve seat sealing ring is quickly pushed to the ball to form a metal-to-metal seal, which has a certain degree of sealing effect. The fire resistance test meets the requirements of AP16FA and API607 standards.
Automatic pressure relief function: When the pressure of the stagnant medium in the valve cavity rises abnormally and exceeds the pre-load of the spring, the valve seat retreats from the sphere to achieve the effect of automatic pressure relief. The valve seat automatically recovers after pressure relief.
Drainage pipeline: Drain holes are set up and down the valve body to check whether the valve seat is leaking. During work, when the valve is fully open or fully closed, the pressure in the middle cavity can be removed, and the packing can be directly replaced; the middle cavity can be discharged. Retentate, reduce the pollution of the medium to the valve.

Main features of fixed ball valve:

advantages of fixed ball valve:

Double blocking and discharge function: the fixed ball valve adopts spring pre-tensioned floating seat, no matter the valve is in the fully open or fully closed state, the upstream and downstream valve seats block the fluid, and the retentate in the valve body is discharged through the discharge valve. .
Automatic pressure relief function: When the temperature of the medium in the valve body cavity increases and causes abnormal pressure rise, it does not need to pass through the safety valve, but the valve seat function can automatically relieve the pressure, which is to ensure the safety of the valve when transporting liquid media. Sex is very important.
Fire safety structure: All valves have fire safety functions, and their design and manufacturing follow the requirements of API 607 and API 6FA.

Disadvantage of fixed ball valve:

Sealing emergency grease injection rescue: due to foreign matter in the medium or fire causing the valve seat seal to fail unexpectedly, the grease injection valve provides a quick connection with the grease injection gun, and the imported pump can easily and quickly inject the sealing grease into the valve seat sealing part. Mitigating leakage.
Reliable valve stem sealing and low operating torque: In addition to the standard sealing ring, an O-ring seal is also set on the packing gland. The double seal ensures the reliability of the valve stem seal; additional graphite packing and sealing grease Injection minimizes valve stem leakage after a fire. The valve stem sliding bearing and thrust bearing make the valve easy to operate.
Full diameter or reduced diameter: Full diameter or reduced diameter structure can be selected according to needs. The flow aperture of the full-bore valve is the same as the inner diameter of the pipeline, which is convenient for pipeline cleaning.
The valve stem can be lengthened: According to the needs of installation or operation, the valve stem can be lengthened. The extended stem ball valve is especially suitable for occasions where pipelines need to be buried in the ground, such as city gas. The size of the lengthened stem is determined according to customer needs.
Flexible operation: The valve seat and stem bearing with small friction coefficient and good self-lubricating property are adopted, which greatly reduces the operating torque of the valve. Therefore, even in the absence of sealing grease, the valve can be operated flexibly for a long time.

Application range of fixed ball valve:

The fixed ball valve is suitable for various pipelines of Class150～Class1500, PN16～PN100, JIS 10K～JIS 20K, applicable temperature: -196～350℃, used to cut off or connect the medium in the pipeline. Different materials can be selected. They are suitable for transporting water, steam, oil, nitric acid, acetic acid, oxidizing media, urea, etc., and are widely used in petroleum refining, long-distance pipelines, chemical industry, papermaking, pharmaceuticals, water conservancy, electric power, municipal administration, steel and other fields. The driving mode of the fixed ball valve is worm gear drive, manual, pneumatic or electric. The fixed ball valve generally adopts flange connection, but also can adopt butt welding connection.

Related types of valves:

We can also produce gate valve, check valve, globe valve, knife gate valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D,

The difference between fixed ball valve and floating ball valve

May 28, 2021

There are many types of ball valves, such as hard-sealed ball valves, soft-sealed ball valves, welded half-ball valves, V-shaped ball valves, flanged ball valves, wafer ball valves, fixed ball valves, and floating ball valves. These classifications are based on the actual use of the manufacturer and the actual situation of the customer. Need, it is slowly researched and developed, but no matter how it develops, it is inseparable from the design principle of the ball valve. The so-called new product of the ball valve, no matter what kind of ball valve is developed, the principle and design plan are designed around the main body of the ball valve. The principles and standards come.
Here, we mainly talk about fixed ball valves and floating ball valves.

14 ball-valve-6

The more intuitive difference between the fixed ball valve and the floating ball valve is that the fixed ball valve is located at the lower end of the valve, and there is a stem supporting hole corresponding to the upper stem. The upper and lower stems firmly fix the spool of the ball valve to make the spool of this valve. Can not roll at will. The sealing principle is that the valve seats on both sides are pressed against the fixed ball core in the middle, so that the valve has a sealing function.
The soft sealing ball valve is round at the lower end of the valve without opening. The ball core is only fixed unilaterally by the upper stem. The ball core can move freely inside the valve cavity. When sealing, the valve seats on both sides of the ball valve are fixed. The valve seat is pressed by the valve core to produce a sealing effect.
Generally speaking, fixed ball valves are suitable for large diameters and high pressure ball valves when the pressure is relatively high. The soft-sealed ball valve is suitable for small caliber, and is suitable for low-pressure sealing ball valve when the pressure is relatively low.
The main feature of the floating ball valve is that the ball has no supporting shaft. The ball is supported by the valve seats at the inlet and outlet ends of the valve. The valve stem and the ball are movably connected. The ball of this ball valve is held in a “floating state” by two valve seats.

The ball can freely rotate between the two valve seats through the valve stem by means of a handle or other driving device.

When the flow channel hole of the ball is aligned with the valve channel hole, the ball valve is in an open state, the fluid is unblocked, and the fluid resistance of the valve is small. When the ball is rotated by 90°C, the flow channel hole of the ball is perpendicular to the valve channel hole, and the ball valve is in a closed state. Under the action of fluid pressure, the ball is pushed to the valve seat at the outlet end of the valve (referred to as the back of the valve) to make it press Tighten and ensure sealing.

Features of floating ball valve:
Under the action of the pressure difference, the ball will move slightly downstream of the valve;
The sealing performance of the ball valve mainly depends on its downstream valve seat;
The valve seat cannot move between the ball and the valve body.

Features of fixed ball valve:

The ball of the fixed ball valve is connected with the upper and lower stems as a whole, or made into an integral connecting ball, that is, the ball is forged (welded) with the upper and lower stems and mounted on the bearing. The ball can be aligned with the valve channel. The vertical axis rotates freely, but cannot move along the channel axis.

Therefore, when the fixed ball valve is working, all the force generated by the fluid pressure in front of the valve on the ball is transmitted to the bearing, and the ball will not move to the rear valve seat, so the valve seat will not bear excessive pressure, so the fixed ball valve The torque is small, the deformation of the valve seat is small, the sealing performance is stable, and the service life is long. It is suitable for high pressure and large diameter occasions.
Function of fixed ball valve
The function of preventing the valve stem from blowing out
Double cut and bleed (DBB) function
Safety function (fire protection function)
The function of injecting sealing grease when the valve leaks
Piston effect of ball valve seat (two-way piston effect of G series ball valve)
The purpose of the two-way piston effect: automatically release the pressure in the cavity of the valve body.
The use of the one-way piston effect: After the upstream valve seat is damaged, the fluid flows into the middle cavity, and the pressure in the middle cavity is higher than the pressure downstream of the valve.
Floating ball valve design should focus on the medium load to be considered in the material of the sealing ring. Excessive medium pressure will affect the life of the valve seat, and the ball can only have a slight offset. Therefore, the floating ball valve is generally suitable for DN200 or below DN200. The ball of the fixed ball valve whose nominal pressure does not exceed CLASS600Lb (10.0MPa) is fixed in the middle of the valve body by the upper and lower stems, and will not move after being pressed. The sealing of the fixed ball valve is to ensure the sealing by providing sufficient pre-tightening force through the leaf spring or cylindrical compression spring on the sealing valve seat, which is a double-sided forced sealing. The ball is supported by the upper and lower bearings, reducing friction, eliminating the excessive torque caused by the huge sealing load formed by the imported pressure pushing the ball and the sealing seat, and the operation is labor-saving. The fixed ball valve is double-sided and sealed on both sides, which will form a sealed cavity between the two sealed valve seats. To avoid danger, the fixed ball valve must be designed with an automatic pressure relief function, that is, when the pressure of the stagnant medium in the valve cavity increases abnormally and exceeds the spring At the time of pre-force, the valve seat retreats away from the sphere to achieve the effect of automatic pressure relief. After pressure relief, the valve seat automatically recovers. The fixed ball valve is widely applicable to various process pipelines with large diameter and high pressure due to its structural characteristics. Due to the need to assemble the upper and lower stems, only ball valves with a nominal diameter of DN50 or above can be produced. The nominal diameter is too small to be assembled.

Structure of fixed ball valve
1). Sphere
After introducing the various structural forms of the seal seat, I came to observe the ball structure of the same ball valve. The most important feature of the Tongding ball valve is that the ball does not deviate from the center of the sphere during the process of storing and opening. The ball I: the design of the pivot has three structural forms:
① the upper part of the sphere has a shaft, and the lower part is a shaft hole for a fixed shaft to insert. The structure of the sphere is a shaft and a hole structure.
② there are two upper and lower shaft holes on the sphere, which are inserted by the upper shaft and the lower shaft respectively. The structure is suitable for small diameters. The insertion depth of the hole is short, and it can only bear a small medium force. The structure is suitable for large diameters, can bear a large medium force, and the supporting journal is separated from the drive shaft. The drive shaft only bears the effect of torque.
③ there are two extending shafts on the sphere, two supporting plates vertically up and down. The medium force is transmitted to the valve body through the journal and the supporting plate. Similarly, the drive shaft only bears a single rotation. The moment action separates the medium force and the operating moment.

2). the valve body

Since the valve body is a forged cylinder, there is no usual valve neck. The valve neck is replaced by a stuffing box. The stuffing box is fixed on the platform of the valve body by bolts. The shaft seal is made of O-shaped rubber ring. The connecting support plate of the valve is also fixed on the valve body through the through hole on the stuffing box. It can be seen that the strength of the valve body in the journal part of this cylindrical structure is greatly weakened.

As for the structure of the valve body, like the floating ball valve, there are two types: side-mounted and top-mounted.

The side-mounted type can be divided into two sections, a main valve body and a secondary valve body structure, or a three-section type, a main valve body and two secondary valve body structures.

The top-mounted valve body is an integral structure. The upper valve cover uses bolts to form a complete pressure boundary with the valve body. The ball is a ball with upper and lower support shafts. The lower support bearing is embedded in the valve body, and the upper support bearing is placed in the valve cover. , The upper shaft end is machined with a groove connected to the flange of the shaft head to transmit torque. The medium force acts on the bearing. The drive shaft only transmits torque. It is designed as a blow-out prevention structure. The design of the valve seat The difficulty of assembly or disassembly is that the valve seat must move to both sides when the ball is installed in the valve cavity. In this way, a slidable back valve seat is designed. The valve seat is retracted into the left and right channels in advance. After the ball is installed, pass the back The flange on the valve pushes the valve seat to the center of the ball, and then uses a snap ring to snap into the groove of the back valve seat. When disassembling, first take out the snap ring, and then push the valve seat into the left and right sides of the valve cavity. In the right channel, the sphere can be taken out from the upper part. Therefore, the top-mounted structural ball has the advantage of being able to be repaired online.

Related types of valves:

Characteristics of ball valve

August 14, 2020

Features of ball valve:
1. Wear resistance; because the valve core of the hard-sealed ball valve is spray-welded alloy steel,

ball valve (2)

The sealing ring is made of alloy steel surfacing, so the hard sealing ball valve will not produce too much wear when opening and closing. (Its hardness coefficient is 65-70):

Second, the sealing performance is good; because the sealing of the hard-seal ball valve is manually ground, it can be used until the valve core and the sealing ring are completely matched. So his sealing performance is reliable.

3. The switch is light; since the bottom of the sealing ring of the hard-sealed ball valve adopts a spring to make the sealing ring and the valve core tightly hug together, the switch is very light when the external force exceeds the preload of the spring.

4. Long service life: It has been widely used in petroleum, chemical industry, power generation, papermaking, atomic energy, aviation, rockets and other departments, as well as people’s daily life.

The pneumatic ball valve has a simple and compact structure, reliable sealing, and convenient maintenance. The sealing surface and the spherical surface are always in a closed state, which is not easy to be eroded by the medium. It is easy to operate and maintain. It is suitable for general working media such as water, solvent, acid and natural gas. It is mainly used for cutting off. Or connect the medium in the pipeline, and can also be used for fluid adjustment and control.

Compared with other types of valves, pneumatic ball valves have angular stroke output torque, quick opening, stable and reliable, wide application, and the following advantages:

1. The thrust bearing reduces the friction torque of the valve stem, which can make the valve stem operate smoothly and flexibly for a long time.

2. Anti-static function: a spring is set between the ball, valve stem and valve body, which can lead out the static electricity generated during the switching process.

3. Since materials such as polytetrafluoroethylene have good self-lubricating properties and small friction loss with the ball, the pneumatic ball valve has a long service life.

4. Small fluid resistance: Pneumatic ball valves have the smallest fluid resistance among all valve categories. Even the reduced diameter pneumatic ball valves have relatively small fluid resistance.

5. Reliable valve stem sealing: Since the valve stem only rotates and does not move up and down, the packing seal of the valve stem is not easy to be damaged, and the sealing ability increases with the increase of the medium pressure.

6. Good sealing performance of the valve seat: The sealing ring made of elastic materials such as polytetrafluoroethylene is easy to seal in structure, and the valve sealing capacity of the pneumatic ball valve increases with the increase of the medium pressure.

7. The fluid resistance is small, and the full-bore ball valve basically has no flow resistance.

8. Simple structure, small size and light weight.

9. Close and reliable. It has two sealing surfaces, and the sealing surface materials of the ball valve are widely used in various plastics, which have good sealing performance and can achieve complete sealing. It has also been widely used in vacuum systems.

10. Convenient operation, rapid opening and closing, only need to rotate 90° from fully open to fully closed, which is convenient for remote control.

11. Convenient maintenance, simple structure of the ball valve, generally movable sealing ring, easy to disassemble and replace.

12. When fully open or fully closed, the sealing surface of the ball and the valve seat is isolated from the medium. When the medium passes, it will not cause erosion of the valve sealing surface.

13. It has a wide range of applications, with a diameter ranging from a few millimeters to a few meters, and can be applied from high vacuum to high pressure.

14. Because the ball valve has wiping properties during opening and closing, it can be used in media with suspended solid particles.

15. The processing precision is high, the cost is expensive, and it is not suitable for use in high temperature. If there are impurities in the pipeline, it is easy to be blocked by the impurities, causing the valve to fail to open.

Posts

V-type regulating ball valve

Properties of Fixed ball valve

The difference between fixed ball valve and floating ball valve

Characteristics of ball valve

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Tag Archive for: features of ball valve

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