PVC Ball Valves
A PVC or polyvinyl chloride ball valve is a plastic on and off valve that has a rotary ball with a bore where turning the ball a quarter turn can stop the flow of a fluid. They are highly durable, cost effective and can be...
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A ball valve is a shut-off valve that allows, obstructs, and controls the flow of liquids, gases, and vapors in a piping system by rotating the ball having a bore inside the valve. The ball is mounted against two seats and has a shaft that connects it to the operating and control mechanism that rotates the ball. When the cross-section of the bore is perpendicular to the area of the flow, the fluid is not permitted to pass through the valve. The fluid flows through from the valve, and the fluid flow rate depends on the area of the bore exposed to the flow.
Ball valves are a type of quarter-turn valve along with plug valves and butterfly valves. They can be operated manually or by using an actuator. The simplest operation of a ball valve is through the use of a wrench or a lever manually turned by an operator. Torque is applied to rotate the lever arm by 900 by either clockwise or counterclockwise to open or close the valve. If the lever arm is parallel to the pipe, it indicates that the valve is open. If the lever arm is perpendicular to the pipe, it indicates that the valve is closed.
Ball valves come in many designs and features to satisfy various industrial needs. The standards and specifications for ball valves vary depending on the industry where it is utilized.
The basic components of a ball valve include the following:
All internal components of a ball valve are contained inside the valve housing or the body. Its primary function is to provide a secure and sealed enclosure for the ball, ensuring that the flow of fluids through the valve can be precisely controlled. The housing typically features inlet and outlet ports, allowing for the connection of pipes or pipelines. It is made of a hard and rigid metal, thermoplastic, or thermoplastic-lined metal that protects the components of the ball valve. This robust construction ensures the reliable operation and longevity of ball valves in various industrial applications.
The ball is a sphere that has a hole in its center. The hole in its center is called the bore. The bore serves as the flow opening of the fluid when the cross-section of the fluid flow path and the bore is coplanar. Otherwise, the flow is throttled. A ball valve may have a solid ball or a hollow ball. A solid ball has a constant opening diameter throughout its structure, which helps the fluid to smoothly flow at a constant velocity. A hollow ball, on the other hand, has a hollow internal structure, and the space inside it allows more fluid to pass through the valve. However, the larger space creates turbulence and high velocities. A hollow ball is lighter and less expensive compared to a solid ball.
The shaft connects the ball to the control mechanism that rotates the ball. When the shaft is turned, it either aligns the ball with the valve's flow path to permit the flow of fluids or positions the ball perpendicular to the flow path to block it completely. The shaft has seals such as O-rings and packing rings to seal the shaft and the bonnet to avoid leakage of the fluid. The shaft's design and construction must be robust to withstand the pressure and temperature conditions of the system, ensuring reliable and efficient operation. The shaft may be manually operated by a lever or a handwheel or operated by an electric, pneumatic, or hydraulic actuation.
The bonnet is an extension of the valve housing that contains and protects the shaft and its packing, which is important in high-pressure and high-temperature applications. It may be welded or bolted to the body. It is also made of hard metal and it covers the opening made from connecting the shaft to the external control mechanism. The bonnet can be removable or integral to the valve body, depending on the valve design.
Ball valves have two seats, typically made of soft materials like PTFE (Teflon) or elastomers. These seats form a tight seal around the ball when the valve is in the closed position. They prevent leakage by creating a secure barrier between the ball and the valve body. The upstream seat seals against pressure, while the downstream seat seals against leakage to the atmosphere.
Electric actuators, also known as motorized actuators, are a method for remotely manipulating ball valves and are used for applications where manual operation of the valve is not possible. The mechanism of an electric actuator can be quarter turn or multi-turn depending on its design. Quarter turn actuators are used for valves that can be completely open or completely closed while multi-turn actuators perform more than one turn and multiple rotations.
The heart of an electric actuator is its electric motor, which is connected to a gear drive that is available with different torque ranges. The gear drive is connected to an output drive that is connected to the valve. Each of the components are housed in a tightly sealed, waterproof enclosure. The operation of an electric actuator is controlled remotely and can have cycle times and duty cycles and include other features to enhance its performance. Additionally, electric actuators can have a network connection or a databus.
Aside from electric actuators, there are also pneumatic actuators that perform the same functions as electric actuators. Pneumatic actuators depend on an air supply for their operation, which limits their use to a discrete set of ball valve applications. Although electric ball valve actuators are more expensive, they have a wider range of use and can be fit to more and varied applications.
Motorized ball valves are used for automated valve control and use an electric motor to open and close the valve. The design of motorized ball valves includes an electric actuator that is bolted to the valve using a mount that is part of the valve body. The electric actuator for motorized ball valves has to rotate 90° to open or close the valve. The motor receives a signal to actuate the motor to open or close the valve.
Depending on the application, positioning of the valve may be necessary in accordance with flow conditions. Under these circumstances, a digital position sensor is used. A microprocessor compares the input signal to the physical position of the valve by an output feedback system and moves the actuator to match the signals.
Motorized ball valves are widely used for remote locations to start and stop material flow. They vary according to the application where they are used and their location, which can be a distance from an application. They offer an efficient and practical solution to ball valve control as well as a labor saving method for material movement.
Pneumatic actuators have the same function as electric actuators but use air as a means of opening and closing a ball valve. They have a housing and horizontal pistons that are connected to a rack and pinion mechanism, which change the linear motion of the pistons to rotary motion. The actuation of the system is caused by compressed air pushing against the pistons. The process of a pneumatic or air actuated ball valve system is simple, reliable, and rugged and costs less than electric actuator systems.
As with electric actuator systems, ball valves for the system have a special mounting attached to the valve for easy installation. Pneumatic actuators operate when they receive air, which is precision controlled. A solenoid is mounted on the actuator with an air line attached to it at its input port. Electric current energizes the solenoid that moves a plunger that opens ports on the actuator to provide air to actuate the valve.
Air actuated ball valves have all of the features associated with electric actuated ball valves including positioners, limiting switches, gear operation, and speed control. Although pneumatic actuated valves are highly durable and reliable, they are limited by their distance from an air supply, which necessitates that they be used in buildings where air is easily accessible.
Ball valves may be classified according to their housing assembly, ball design, and bore profile.
A one-piece ball valve has a single-piece cast body that houses the internal components of the ball valve. This eliminates the risk of leakage of the fluid from the valve. One-piece ball valves are the cheapest ball valves and always have a reduced bore. A welded one-piece ball valve is more common but cannot be dismantled for cleaning and repaired once damaged; therefore, it is only used for applications with a low possibility of particle build-up, and where sanitation is not a major concern. On the other hand, screwed one-piece ball valves can be cleaned, serviced, and repaired, but dismantling requires special tools.
Split Body Ball Valves are valves that are assembled on the sides of their balls. A split body ball valve may be a two-piece or a three-piece ball valve:
A two-piece ball valve consists of housing divided into two pieces that are fitted together. The main piece contains the ball and a connection to one end, and the other piece holds the internal components together and has a connection to the other end. Two-piece housing is the most common type among ball valves. The two parts can be dismantled for cleaning, maintenance, and inspection but it requires removal of the valve from the pipe.
A three-piece ball valve consists of the housing for the internal components of the valve which are fitted and held together by bolt connections to its two ends. The ends are threaded or welded to the main pipe.
Three-piece ball valves are used for applications that require a valve that can be cleaned and serviced easily. The seats and seals of three-piece ball valves can be routinely replaced by taking the valve body out without disturbing the two ends. Three-piece ball valves are commonly used in the food and beverage and pharmaceutical industries where sanitation is crucial to safety and product quality.
A top entry ball valve allows access to the internals of the valve by simply removing the bonnet on top of the valve. This allows in-line maintenance activities (i.e., dismantling, cleaning, inspection, and repairing the valve) without removing the ball valve from the main pipe.
The floating ball is the most common ball design in ball valves. The ball is suspended inside the valve and free to move in a lateral direction when the valve is in a closed position. It is sandwiched between two seats that support the valve and hold it in place. The ball is connected to the shaft in a slot on one end while the other end is free. When the valve is in an open position, the shaft connection to the slot at the top of the ball prevents the ball from moving laterally.
The sealing action is only dependent on fluid pressure. During an operation of a floating ball valve, the inlet pressure of the fluid forces the ball to the outlet seat which prevents the fluid from escaping from the valve body. The fluid pressure on the ball and the seats are higher when the ball valve is in the closed position.
Floating ball valves have the simplest design. They come in smaller diameters and are suitable for liquids and gases operating under low to moderate pressures. The application of floating ball valves is limited by the amount of pressure the seats can handle. At high fluid pressure, the seats can be deformed from the pressure exerted by the ball which can affect the sealing characteristics of the valve under low pressure. Furthermore, the torque to rotate the shaft depends on the force required to counteract the same fluid force acting on the ball and seals.
In a trunnion ball valve, the ball is supported by an additional shaft at its bottom which is called the trunnion. This holds the ball in its place and limits the movement of the ball to its axis. The ball can only move if the valve shaft rotates. Trunnion ball valves also feature spring-loaded seats. The inlet fluid pressure activates the springs towards the ball held by the trunnion, which creates a tight sealing.
Trunnion ball valves are available in small to large diameters, but it is more expensive than floating ball designs. They can operate efficiently in a wide range of pressures and they are ideal for high-pressure applications since the fluid pressure is also dissipated to the trunnion and the springs of the seats. Hence, they are easier to operate with a lower operating torque or a small actuator.
A vented ball valve is constructed and operates in the same way as a standard ball valve, except that the vented ball has small orifices drilled into its side. When the valve is closed, the orifice is directed to the outlet side of the valve. The drilled hole is used to vent trapped gases which causes a build-up of internal pressure inside the valve, to prevent leaking, valve failure, and explosion.
Vented ball valves are used in compressed air systems, cryogenic processing and conveying volatile liquids are also referred to as the “cryogenic valve” because of their usefulness in cryogenic processing.
A full bore has a bore diameter similar to the pipe diameter. The flow area for the fluid for full bore valves remains constant, therefore the flow resistance offered by this type is very low. Minimal frictional loss is encountered during fluid flow; hence the pressure drop is low. A high pressure drop in a piping system causes pumping more difficult. However, since the bore diameter should be equal to the pipe size, it requires a larger ball size and housing which makes it more expensive than a reduced bore.
Full bore ball valves are easier to maintain and clean. In pipelines, the pipes are maintained and inspected by an operation called pigging. A spherical or cylindrical device called pigs is allowed to flow in the pipes to detect and remove any build-up without interfering with the fluid inside the pipeline. This operation is possible with an installed full-bore ball valve.
Full bore ball valves are also used in conveying liquids with mixed solids where flow restrictions cause the build-up of particles that can eventually cause separation of the mixtures that will flow through it.
A reduced bore has a bore diameter smaller by a pipe size than the (connection) pipe diameter. The actual reduction is determined by the agreement between the manufacturer and the customer. The flow area for the fluid becomes narrower at the outlet, therefore there are frictional losses that are introduced which result in a pressure drop. Since the amount of flow discharge remains constant, the velocity increases with the decrease in the flow area.
Reduced bore ball valves are more common than full bore ball valves. They are used in applications where product flow rate and turbulence are not potential concerns and particle build-up is not likely to occur. The reduced bore is less expensive than the full bore since it requires a smaller ball size and housing. Compared to other types of valves, the reduced bore ball valves have relatively smaller pressure drop.
A segmented ball valve has a V-shaped notch on its ball. A segmented ball valve has good flow rate control which depends on the ball rotation. Aside from that, it also has a good shut-off capability. The flow characteristic in a segment ball valve approaches an equal percentage flow characteristic. The flow rate in a segmented ball valve increases exponentially as the ball reaches its fully opened position.
A cavity-filled ball valve has a seat design that fills the gap between the ball and its body. This eliminates the possibility of entrapped media or particle build-up over time around the ball which can cause contamination or blocking of the fluid flow. Cavity-filled ball valves are easier to clean and maintain.
Cavity-filled ball valves are valuable in industries where sanitation is crucial, such as in food, pharmaceutical, and bioprocessing industries. They are ideal in handling solid-liquid mixtures such as slurries.
Multi-port ball valves are used in diverting, combining, splitting, or shutting off multiple fluid streams through the use of a ball with an L-shaped or T-shaped bore through their middle. Flow to the inlet of a multiport valve is split into multiple outlet streams but cannot distribute the flow to its outlet streams at predetermined flow rates. Multi-port ball valves can join multiple flow streams into a single stream or change the direction of the flow. The schematic diagram below shows possible flow configurations of an L-shaped and a T-shaped multi-port ball valve.
The different types of 3-way ball valves have three ports or openings to capture fluid flow. At the head of the three ports is a metal ball with openings that are designed to control fluid flow. As fluid or gas enters the valve, a mechanism rotates the ball to direct the flow. The designs of 3-way ball valves vary between ones that have two outlet ports and one inlet port and ones with two inlet ports and one outlet port.
Three-way ball valves are classified like multi-port valves and can have a L configuration or T configuration. They can perform several different functions including switching fluid flow, mixing flow, stopping flow while allowing flow, diverting flow, and stopping flow from all directions. When a 3-way ball valve is mixing material, the flow enters from different directions and co-mingles in the valve.
The different types of 3-way ball valves have three ports or openings to capture fluid flow. At the head of the three ports is a metal ball with openings that are designed to control fluid flow. As fluid or gas enters the valve, a mechanism rotates the ball to direct the flow. The designs of 3-way ball valves vary between ones that have two outlet ports and one inlet port and ones with two inlet ports and one outlet port.
Three-way ball valves are classified like multi-port valves and can have a L configuration or T configuration. They can perform several different functions including switching fluid flow, mixing flow, stopping flow while allowing flow, diverting flow, and stopping flow from all directions. When a 3-way ball valve is mixing material, the flow enters from different directions and co-mingles in the valve.
Sanitary ball valves have to meet a set of highly restrictive stipulations regarding sterility, cleanliness, and hygiene. They are a type of ball valve that meet the health and safety standards for food, beverage, medical, pharmaceutical, and other forms of applications that have health requirements for microbial bacteria control. Sanitary ball valves are able to meet the sterile performance standards for the handling of substances that have to maintain their purity during processing.
The valve body of sanitary ball valves is made of series 304 or series 316 stainless steel. Of the two series, 304 is the most widely used for hospitals, food processing, and pharmaceuticals due to its clean smooth surface and ability to be cleaned multiple times without experiencing wear. A necessity for sanitary ball valves is their ability to be frequently assembled, disassembled, cleaned, reassembled, and installed to prevent the growth of microbial organisms and contaminants.
Sanitary ball valves are designed to prevent the risk of biological, chemical, or physical hazards. Threaded connections are not used due to the difficulty of cleaning them and the potential of their containing contaminants. Seals, O-rings, and seats of sanitary ball valves are made of inert and abrasion resistant materials such as polytetrafluoroethylene (PTFE or Teflon).
The typical geometry of ball valves includes a dead spot between the valve seat and ball. This aspect of a ball valve provides a space for bacteria to grow, which has to be removed from sanitary ball valves. For sanitary ball valves, cavity filled ball seats are used where the dead spot is filled with PTFE. In addition, surfaces of sanitary ball valves are polished and finished to eliminate any peaks and values with Ra levels of 8 up to 32.
The ball valve’s ball and its housing are commonly constructed from the following materials:
Brass is an alloy of copper and zinc that can be distinguished by its dull yellowish to reddish color, depending on the amount of zinc. It is the most common material for ball valves. Brass is a tough, strong, and durable metal that can withstand high temperatures and pressures. The copper in brass alloy has antimicrobial properties that inhibit the growth and reproduction of microbes on its surface. Brass has good chemical, corrosion, and biofouling resistance. It is inert to most acids, alkalis, and bases, except for solutions with high chlorine content. Chlorine can cause dezincification, a reaction where chloride ions strip away zinc from the alloy, causing a porous structure. Dezincification can drastically reduce the strength of the material.
Brass ball valves are not difficult to fabricate because of their malleability, and they are also easy to cast and weld. They are lighter and cheaper than steel ball valves. They are also easy to assemble in the piping system. Common applications of brass ball valves are in food, chemical, and oil and gas processing, and in conveying gaseous fluids. It is also safe to use in the delivery of potable drinking water.
Stainless steel is a type of steel that contains higher chromium content and some amounts of nickel. The chromium content of stainless steel makes it acquire a superior corrosion resistance. Stainless steel is known for its excellent strength, toughness, and durability. It also retains its strength in high temperatures and pressures.
Stainless steel ball valves are commonly constructed in 304 and 316 Stainless Steel grades. The 304 Stainless Steel has 18% chromium and 8% nickel, while 316 Stainless Steel has 18% chromium and 10% nickel and trace amounts of molybdenum. The combination of nickel and molybdenum makes the 316 Stainless Steel resistant to chlorides.
There are applications where the use of a stainless-steel ball valve is an excellent choice. They are used in swimming pools to handle chlorinated water. In harsh industrial environments such as desalination and petroleum refining plants, they offer better resistance to corrosive chemicals under high temperatures and pressures. In breweries, stainless steel pipes and valves are used to handle wort, a reactive liquid that is extracted during the mashing process.
PVC is a tough, rigid and durable plastic material. Compared to brass and stainless-steel alloys, they generally have lower strength but they are cheaper. They are resistant to corrosion and most acids, bases, and salt solutions. However, they are not resistant to aromatic compounds and hydrocarbons. PVC ball valves (*) have a lower temperature and pressure rating, for up to 150 psi and 140°F, respectively. Application of PVC ball valves includes plumbing, irrigation, and water distribution systems.
Chlorinated PVC (CPVC) is a type of PVC that has been chlorinated by a free radical reaction initiated by UV light. The chlorination of PVC results in higher temperature resistance. CPVC ball valves can handle higher temperatures of up to 200°F.
PP is a tough, durable, lightweight, and flexible thermoplastic made from propylene monomer. It offers good resistance to most acids and bases, but has selective compatibility with organic substances and solvents. Its chemical resistance decreases with increasing temperatures. The maximum operating temperature of PP is 82°C. PP ball valves are suitable for regulating the flow of fluids with a wide range of viscosity. They are used as materials for ball valves in the manufacturing of sugar, fertilizers, chemicals, paper, and others.
In GFPPs, glass fibers are reinforced to polypropylene to increase its dimensional stability, rigidity, and chemical resistance, and to reduce the PP’s coefficient of thermal expansion. Its heat deflection temperature is increased up to 1500C for a 40% GFPP at 264 psi. Reinforcement of glass fibers in PP increases cost-efficiency and makes it operate in more harsher and heavy-duty applications.
PVDF is a high purity, durable, thermoplastic fluoropolymer with high molecular weight. It is synthesized from gaseous vinylidene fluoride monomer by a free-radical polymerization process. It is also resistant to abrasion.
This material has excellent chemical resistance that makes it suitable for handling reactive liquids and gaseous substances such as sulfuric acid, hydrochloric acid, nitric acid, hydrocarbons, fuels, and solvents that are aromatic, aliphatic, and halogenated in nature. It is used as a material for ball valves in industries such as water purification, wastewater treatment, and in food and pharmaceutical processing because of its good biofouling properties that is resistant to the growth of microbial films. It also remains unaffected by exposure to sunlight and UV. The maximum operating temperature of PVDF is around 115°C.
PE is a durable, flexible, lightweight, and the most abundant thermoplastic. PE is compatible with most compounds, including strong acids and bases, and to some organic compounds including oils and alcohols. Its increasing crystallinity and density makes it more chemical resistant. PE ball valves are used in handling fluids in many manufacturing processes, as well as in water purification and wastewater treatment. The maximum operating temperature of PVDF is around 60°C.
The seat is made from elastomeric material or plastic or a metal, for better sealing with the ball. A qualified seat material must also possess the following characteristics:
Examples of seat materials for ball valves are
A metal-seated ball valve has the ability to withstand higher temperatures and hydraulic pressures. They can handle abrasive and corrosive fluids better.
Ball valves offer several benefits in various applications due to their design and functionality. Some of the key advantages of using ball valves include:
There are several limitations the user must remember to preserve the functionality of the ball valve:
Standard ball valves may be used in throttling low pressure gases. Segmented ball valves may be used in limited throttling applications.
However, advanced ball valves with modified designs or seats made from engineered materials that are suitable for throttling applications are commercially available.
A PVC or polyvinyl chloride ball valve is a plastic on and off valve that has a rotary ball with a bore where turning the ball a quarter turn can stop the flow of a fluid. They are highly durable, cost effective and can be...
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A spring check valve is a valve that ensures unidirectional flow and prevents reverse flow. They have a single inlet and outlet and must be placed in proper orientation to function correctly. On the side of a spring check valve, and all...