Butterfly Valve Introduction Guide
Butterfly Valve Introduction Guide
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The invention of the butterfly valve has allowed for the improvement of processes and applications in various industries. This introductory guide is intended to familiarize you with what a butterfly valve is, how it works, and its design variations.
What is a Butterfly Valve?
A butterfly valve is a mechanism that regulates the flow of materials within large pipe diameters by the quarter-turn rotation of a disc.
A rod feeds through the center of a disc and this rod is connected to an actuator that controls the motion of the disc. The disc position is either parallel or perpendicular to the flow of media. A butterfly valve differs from other valves because the disc is always in the flow causing a pressure change for any position of the valve.
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Why is it Called a Butterfly Valve?
Some valves are named for their shape such as ball valve, globe valve, needle valve, etc. Other valves are named for their movement and function &#; gate valve, plug valve, pinch valve, life valve, slide valve, etc. A butterfly control valve is also named for the movement it makes.
The butterfly valve gets its name from how the movement is similar to a wing for flight. The rod is analogous to a butterfly&#;s body, while the disc moves like a butterfly wing. A butterfly valve&#;s motion is similar to that of a butterfly that has landed with the wings moved up and down with a 90-degree motion.
What is a Butterfly Valve Used For?
A butterfly valve regulates flow by starting, slowing, or stopping media. The disk opens and closes with a low-torque rotation of 90 degrees and works for any compatible application. Because they cost less and are lighter weight, the butterfly valve is often preferred over other types of valves.
For some processes, extreme temperatures and corrosion are factors that would easily compromise a valve&#;s seal. The butterfly valve withstands extreme cold or extreme heat. This means the seal maintains its integrity which is critical for high-stakes applications such as energy production and petroleum processing (as one leak could threaten public safety or the environment).
Principle of Operation
The butterfly valve is classified as a quarter-turn valve. It works like a ball valve for quick shutoff, but unlike a ball valve, the butterfly valve can also open and close incrementally. This difference means that the disc is always present in the flow and allows for a drop in pressure.
This disc is mounted at the center of the pipe. Disc movement is controlled by a rod inserted through the disc and an actuator, located outside the valve. Turning the actuator positions the disc either perpendicular or parallel to the flow.
Where is the Butterfly Valve Located?
For butterfly valve parts orientation, there are some standard guidelines. The butterfly valve needs some distance from other parts such as pumps, elbows, and other valves &#; 6 pipe diameter separation is ideal.
Usually, the butterfly valve is installed with the valve stem oriented vertically with the actuator directly above it, but in some cases, the stem is situated horizontally instead. When connected to a pump or check valve, there must be clearance for the disc so it doesn&#;t interfere with other parts nearby.
3 Main Butterfly Valve Types
While these valves all do essentially the same function, there are variations of butterfly valve design to suit different operations. Below are the three main butterfly valve types.
Zero-offset Butterfly Valve
&#;Concentric&#; or &#;rubber seated&#; are other names for the zero-offset design. Zero-offset means there is no offset by the stem of the valve. The valve seals via interference along the disc edge at the stem between the disc and the rubber seat.
The rubber seated valve has the lowest pressure rating (up to 250 PSI) and withstands heat up to 400°F. Its rubber seat encases the body to prevent contact with the material which maintains the purity of the media.
High-Performance Double Offset Butterfly Valve
This butterfly valve is referred to as a double offset because the offset is in two places: at the line of the disc seat /body seal, and at the bore. Off-center positioning increases durability for the seal. High-performance valves tolerate pressure up to PSI and temps up to °F.
A cam-action occurs from the stem being behind the disc as it rubs against the during rotation at 90° for the first 10 degrees of opening, but also for the 10 degrees of closing.
Triple Offset Butterfly Valve
The best type of butterfly valve for high-pressure systems is the triple offset butterfly valve. Of the three types, the triple offset is the most advanced with lower emissions and is designed to work with various environments. Its heat tolerance is °F as it can withstand 1,480 PSI of pressure.
Like the double offset valve, the triple offset valve consists of two offsets situated in the center, but with a third offset having cam action with right-angled conical sealing. It is frictionless and long-wearing by the metal seal components not making contact until their final point.
Common Butterfly Valve Applications
Some processes need more tolerant and wear-resistant valves with special features. Below are some common applications that rely on the unique mechanisms of a butterfly control valve.
Food Processing
Simple design, high durability, and low maintenance are the features needed to regulate fluid flow in any piping system. Certified Food Grade Seat is best for the Food Processing sector, so a White seat is preferred.
While standard resilient seated valves are not 3A approved, there are many on the market that maintain sanitary connections inside and outside. The body material for the valve can range from Epoxy coated iron to Nylon 11 coated iron to Bronze, 304SS, and 316SS.
Refineries
The butterfly valve is commonly found in refineries. These would typically use the more &#;high end&#; High-Performance valve with Steel Bodies, or the Triple Offset design that is &#;Fire Safe&#; and bubble tight. Many applications involving water use the resiliently seated version.
Shut Off Valves
A butterfly valve is often the best choice as a general shut-off valve above 1.5&#;-148&#;. Their simple design allows them to take up less space and less weight than other types of valves. These valves provide a tighter seal than a gate of globe valve and are usually bubble tight. This is most useful when trying to stop the fluid flow as it prevents any fluid from passing through the pipe when closed.
Ship Building
Because of their high durability in saltwater, butterfly valves are commonly used in ships where ABS-approved materials are selected. This type of valve effectively creates a water-tight shutoff in the piping system of a ship to prevent any flow in the pipe. Their small size also allows them to be used in those tight spaces that are common aboard the ship.
They can be used for &#;jack up&#; rigs, ballast systems, ship side, and many other applications. Fire Safe approved valves are also necessary for many applications. Additional capabilities are automation and pneumatic function (&#;closed-loop&#; pneumatic underwater, electric, and hydraulic).
Be sure to use valves with an ISO- mounting pad and stem. This way it&#;s easier to get a drop-in replacement at any port. Also, be wary of valves that just have an ISO- mounting pad as the stems are often manufacturer&#;s &#;special.&#;
Butterfly valve
Flow control device
Duplex valve in wafer butterfly configuration.
in wafer butterfly configuration.
A butterfly valve is a valve that isolates or regulates the flow of a fluid. The closing mechanism is a disk that rotates.
Principle of operation
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Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they cost less than other valve designs, and are lighter weight so they need less support. The disc is positioned in the center of the pipe. A rod passes through the disc to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow, so it induces a pressure drop, even when open.
A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid. The valve may also be opened incrementally to throttle flow.
There are different kinds of butterfly valves, each adapted for different pressures and different usage. The zero-offset butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high-performance double offset butterfly valve, used in slightly higher-pressure systems, is offset from the center line of the disc seat and body seal (offset one), and the center line of the bore (offset two). This creates a cam action during operation to lift the seat out of the seal resulting in less friction than is created in the zero offset design and decreases its tendency to wear. The valve best suited for high-pressure systems is the triple offset butterfly valve. In this valve, the disc seat contact axis is offset, which acts to virtually eliminate sliding contact between disc and seat. In the case of triple offset valves the seat is made of metal so that it can be machined such as to achieve a bubble-tight shut-off when in contact with the disc.
Types
Concentric butterfly valves &#; this type of valve has a resilient rubber seat with a metal disc.
Doubly-eccentric butterfly valves (high-performance butterfly valves or double-offset butterfly valves) &#; different type of materials is used for seat and disc.
Triply-eccentric butterfly valves (triple-offset butterfly valves) &#; the seats are either laminated or solid metal seat design.
Wafer-style butterfly valve
The wafer style butterfly valve is designed to maintain a seal against bi-directional pressure differential to prevent any backflow in systems designed for unidirectional flow. It accomplishes this with a tightly fitting seal; i.e., gasket, o-ring, precision machined, and a flat valve face on the upstream and downstream sides of the valve.the drawback is that wafer butterfly valves only have a small flow control range. The pressure drop across wafer butterfly valves may be greater. Wafer butterfly valves are prone to clogging due to their design.[1]
Lug-style butterfly valve
Lug-style valves have threaded inserts at both sides of the valve body. This allows them to be installed into a system using two sets of bolts and no nuts. The valve is installed between two flanges using a separate set of bolts for each flange. This setup permits either side of the piping system to be disconnected without disturbing the other side.
A lug-style butterfly valve used in dead end service generally has a reduced pressure rating. For example, a lug-style butterfly valve mounted between two flanges has a 1,000 kPa (150 psi) pressure rating. The same valve mounted with one flange, in dead end service, has a 520 kPa (75 psi) rating. Lugged valves are extremely resistant to chemicals and solvents and can handle temperatures up to 200 °C, which makes it a versatile solution.
Rotary valve
Rotary valves constitute a derivation of the general butterfly valves and are used mainly in powder processing industries. Instead of being flat, the butterfly is equipped with pockets. When closed, it acts exactly like a butterfly valve and is tight. But when it is in the rotation, the pockets allow dropping a defined amount of solids,[2] which makes the valve suitable for dosing bulk product by gravity. Such valves are usually of small size (less than 300 mm), pneumatically activated and rotate 180 degrees back and forth.
Use in industry
In the pharmaceutical, chemical, and food industries, a butterfly valve is used to interrupt product flow (solid, liquid, gas) within the process.[3] The valves used in these industries are usually manufactured according to cGMP guidelines (current good manufacturing practise). Butterfly valves generally replaced ball valves in many industries, particularly petroleum, due to lower cost and ease of installation, but pipelines containing butterfly valves cannot be 'pigged' for cleaning.
The butterfly valve has been in use since the late 18th century. James Watt used a butterfly valve in his steam engine prototypes. With advances in material manufacturing and technology, butterfly valves could be made smaller and withstand more-extreme temperatures. After World War II, synthetic rubbers were used in the sealer members, allowing the butterfly valve to be used in many more industries.[4] In James E. Hemphill patented an improvement to the butterfly valve, reducing the hydrodynamic torque needed to change the output of the valve.[5]
Valve Design and Working Principle of Butterfly Valve
A butterfly valve is used to isolate or regulate the flow of a fluid. It can be used for a wide range of applications such as water supply, wastewater treatment, and fire protection, for chemical and fuel industries and many more.
Butterfly Valve Working Principle
It is based on the quick shut off principle. The disc of the valve is placed in the center of the pipe which allows a rod to go through it to an actuator, on the outer side of the valve. The disc remains parallel or perpendicular to the flow. A pressure drop is introduced by the disc upon the flow even when open.
It open or closed when the disc is rotated a quarter turn and hence it is also known as a quarter-turn valve. There is a metal disc on the rod and when the valve is closed it blocks the passageway by giving it a quarter turn. This metal disc is known as a butterfly. It is the most important component of the valve.
Butterfly valve classification
Butterfly valves are quick to open type valves used to stop, regulate and start the flow of the fluid. A gearbox type actuator is attached with large butterfly valves and a hand wheel is connected to the stem of the valve via a gearbox. The butterfly valve is classified into four types.
Centric Butterfly valves: Centric butterfly valves are also known as soft seated valves. They are used for low- pressure and non- critical applications in gate and ball valves. They are very cost-efficient and easy to install. Centric butterfly valves are also very lightweight.
Motorized butterfly valve: Motorized butterfly valves are used to control the media flowing through the pipelines of the system. By changing the position of a round disc within a pipeline, it starts operating. They are available in many different sizes and they can be fit into any type of specifications.
are used to control the media flowing through the pipelines of the system. By changing the position of a round disc within a pipeline, it starts operating. They are available in many different sizes and they can be fit into any type of specifications.
`Pre-insulated butterfly valves:
Pre-insulated butterfly valves avoid the cost as well as manpower for insulating the valve after installation. They are made up of very fine quality materials. They are of very simple design and enhance durability. Pre-insulated valves have a long service life and they are crack resistance.
Wafer type butterfly valve: pipe flanges and the flange bolts encircle the valve body.
wafer type butterfly valve is very easy to install into the system but it does not work as an isolation valve. It is placed betweenencircle the valve body.
Butterfly valves design
The butterfly valve comes into two designs, centric and eccentric. The only difference between these two designs is, in centric butterfly valve stem is placed in the center of the disc and disc is placed in the center of the bore. Whereas in eccentric butterfly valves, there can be more than one stem placed offset from the center.
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