What is Butterfly Valve? | How does a Butterfly Valve work?

The valves are used all over the world to open, close or regulate the fluid flow. They are used for different industrial and residential applications. There are many types of valves, and a butterfly valve is one of them. The butterfly valves are used to open, regulate or close the flow of fluids. These are fast operating valves. They open and close very quickly. This article explains the butterfly valve working, types, parts, and some other aspects.

What is a Butterfly Valve?

A butterfly valve is a quarter-turn valve used to open, close, and regulate fluid flow. It has an easy operation. The 90-degree rotation of the valve handwheel or actuator fully opens or closes the fluid flow. 

The valve has a disk. This disk installs on a rotary shaft. As you turn the handwheel to stop the fluid flow, the valve disk moves down and blocks the flow. In the fully open condition, the valve disk makes a 90 degrees angle to the fluid flow.

The large butterfly valves have a gearbox in which the handle connects to the valve stem via gears. This design makes the valve operation simple and easy but reduces the operating speed.   

These types of valves have a quick operation, light weight, simple in design, small in size, lower costs, and small installation footprint. Therefore, the butterfly valves are most commonly used for municipal engineering, septic tanks, building water pipelines, environmental protection, and hydropower applications. You can also use an automatic actuator, gears, or handles to operate them.

Working of Butterfly Valve

The working of the butterfly valve is very similar as a ball valve. The butterfly valves are most famous because they have light weight, low cost, easy and quick operation. A butterfly valve has a metal disk that is attached to a stem. This disk always presents in the flow due to that it increases the pressure drop.

A handwheel or actuator uses to turn this disk. The valve disk receives motion by the stem to open or close the fluid flow.

butterfly valve working

A butterfly valve works in the following way:

  • When the valve operator turns the handle clockwise up to 90 degrees, the handle transfers its motion to the steam.
  • As the stem receives handle motion, it turns the valve disk.
  • As the disk receives clockwise motion, it turns and sits in between the valve seats and makes a perpendicular angle to the flow; due to that, it fully stops the fluid flow.
  • As the operator wishes to open the valve fully, he turns the handle in an anticlockwise direction up to 90 degrees.
  • As the disk gets anticlockwise motion by the handle, it moves away from the valve seat, makes a parallel angle to the fluid flow, and allows the fluid to flow.
  • The operator turns the disc in partial open and close conditions for throttle flow.

Types of Butterfly Valves

The butterfly valve has the following major types:

  1. Concentric valve
  2. Eccentric valve
  3. Wafer valve
  4. Lug-style valve
  5. Rotary valve

1) Concentric Valve

A concentric valve is a fundamental and most common type of butterfly valve. This valve stem connects to the disk. The stem passes through the centerline of the disk. This disk presents in the center of the pipe hole, and the valve seat locates inside the valve body.

Concentric valve
Image Source (iqsdirectory.com)

The zero-offset valve design is also known as a resilient seated valve as it depends on the rubber seat flexibility to effectively seal the fluid flow when shut-off.

When the valve disk rotates through 90 degrees, it first contacts the valve seat at an angle of approximately 85 degrees. These types of the butterfly valve are used for low-pressure applications.

Advantages and Disadvantages of Concentric Valve

Advantages of Concentric Valve
  1. It has a neutral seal structure.
  2. The top and bottom ends of the valve disk near the stem are designed as two smooth flat surfaces that are in close contact with the rubber seat ring to prevent media from leaking at both ends.
  3. This valve seat seal has a soft seal design resin skeleton and rubber.
Disadvantages of Concentric Valve
  1. Due to their structural properties, these butterfly valves can only be soft-seated butterfly valves.
  2. You can only use them in normal and low-temperature working environments.
  3. These are not ideal for high pressure and high-temperature working environment.

2) Rotary Valve

These valves are most commonly employed to regulate the product flow, usually to decrease the flow rate up to the desired level of the system. They are most commonly used in high-performance engines.

Rotary valve

These butterfly valves most commonly use in the following applications:

  1. Powder processing industry
  2. To change the brass instruments pitch
  3. To control the exhaust port and steam port of the steam engine
  4. To reverse the air and fuel flow across the open-hearth furnaces.
  5. Some specific types of 4-stroke engines and 2-stroke engines.

Advantages and Disadvantages of Rotary Valve

Advantages of Rotary Valve
  1. They provide a precise opening and closing.
  2. It has a short length of intake.
  3. It doesn’t provide a complex passageway to feed the engine.
Disadvantages of Rotary Valve
  1. The efficiency of the valve reduces by increasing the motor speed.
  2. These valves can’t flow materials. They just pass the material which may fall into them.

3) Eccentric Valve

An eccentric butterfly valve includes in the most famous butterfly valve types. The stems of these valves don’t pass through the disk centerline.

Eccentric valve

The ecentric valves have the following three types:

  1. Single Eccentric Valve: If the valve stem installs just behind the disk centerline, the valve is known as a single eccentric valve. This type of valve is designed to decrease the contact between the seal and the disk before the valve is fully closed. This design extends the service life of the valve. Nowadays, a single eccentric valve has been replaced by double and triple eccentric valves.
  2. Double Eccentric Valve: In double eccentric valves, the valve stem installs behind the disk with an extra offset to one side. The double eccentric permits the disk to self-adjust to the center, which ensures a tight seal. This double offset of the valve stem allows the moving disk to rub the valve seat only 1 to 3 degrees. It doesn’t make contact with the soft seats even in fully open condition.
  3. Triple Eccentric Valve: These valves mostly use for critical applications. These valves have the same design as double eccentric valves. The two offsets of this valve are similar as the double eccentric valve, while 3rdoffset is the contact axis of the disk seat. This valve has a tapered design seat. These valves have less wear and high efficiency. They have a metal seat to make a tight shut-off. This metal sheet enables the valve to work in a higher temperature range.

The eccentric valves are used for paper and pulp industries, power, petroleum refining, mining, and slurry applications.

Advantages of Eccentric Valve

  1. Frictionless closing and opening
  2. High-temperature resistance
  3. Quick operation

4) Lug-style Butterfly Valve

This butterfly valve design has threads on both sides of the valve body. These threads help to install the valve into the systems without using nuts. You just need two sets of bolts to install them.

Lug style butterfly valve

The lug-style valve connects between the two flanges, each with a separate set of bolts. This configuration allows you to remove one side of the system without disturbing the other side.

These butterfly valves are used for dead-end services generally have lower pressure ratings. They are a versatile solution as they are highly resistant to solvents and chemicals and can withstand maximum temperatures (i.e., 200°C).

5) Wafer-style Valve

This type of butterfly valve has low cost than other types. It clamps between two pipe flanges. Some wafer-style valves have a flanged hole outside of the housing, while remaining valves don’t have flanged holes.

The pipe flange is attached with long bolts that cross the whole body of the valve. A gasket is installed between the pipe flange and the valve to achieve a leak-free seal.

Wafer butterfly valve

An O-ring uses to seal the stem. This design is manufactured to seal bidirectional pressure differentials and stop backflow in a system designed for collective flow.

Construction of Butterfly Valve

The butterfly valve has an easy and simple construction. It consists of a handwheel/actuator, stem, disk, gasket, and body. The disk is connected to the stem, which further connects to the handwheel.

The handwheel uses for manual valves, while electric valves use actuators.

The rotation of the valve disc controls the flow. When you turn the handwheel to close the valve, the disc becomes parallel to the flow direction, blocks the valve opening, and stops the fluid flow. However, in the fully open position, the disc becomes perpendicular to the direction of flow and allows flow.

These types of valves offer bidirectional flow and shut-off features. However, it is not a full drill valve. Therefore, it is unsuitable for swabbing or pigging.

The ductile cast iron is used to construct the valve body and an epoxy powder is coated on the exterior and interior surfaces.

Parts of the Butterfly Valve

The butterfly valve consists of the following parts:

  1. Stem
  2. Handwheel
  3. Disk
  4. Seat
  5. Body
  6. Bolt thread
  7. Pins
  8. Stem sealing 
  9. Bushing

parts of butterfly valve

1) Body

These valves typically have a body mounted between two pipe flanges. The lug and wafer are the most commonly used designs of the body. 

2) Valve Disk

The disk is a most major part of the butterfly valve. The proper operation of the disk is very important for the proper working of the valve. It uses to stop or start the fluid flow. 

It works the same as a ball of a ball valve, a gate in a gate valve, and the plug of a shut-off plug valve. The disk connects to the stem of the valve.

3) Stem

The butterfly valve stem has a single piece or double piece (split stem) design. In the case of the more flexible design of the valve seat, the valve stem is sensitive to fluids, which enables the choice of material according to mechanical properties and costs.

One end of the valve stem connects to the handwheel or actuator, while the other end connects to the valve disk. It gets motion by the handwheel and transfers this motion to the disk.

4) Seats

The butterfly valve has two seats. As the operator turns the handwheel to stop the fluid flow, the disk sits in between these two seats and block the flow. Seats are made of various polymers or elastomers. This seat can be locked, pressed, or bonded onto the valve body.

5) Handwheel

The handwheel is used in a manual valve. It is connected to the stem. As you turn the handwheel, it turns the disk to open or close the valve according to your desire. 

Read More: Different types of Ball Valves

Butterfly Valve Actuation

You can actuate or operate the butterfly valves through different that vary according to the nature of the application. Following are the most common methods to operate butterfly valves:

  1. Electricity: In this method, an electric actuator uses to control the valve with a 4mA to 20mA control signal. This method typically uses for time-sensitive and high precise regulation
  2. Manual: In the manual method, a level, crank, or handwheel uses to actuate the valve. Small manual valves usually have a lever. The larger size valves use a flywheel and gears to transmit torque with great mechanical advantage. Some valves have a handwheel.
  3. Hydraulic: This actuation method uses for systems that require high torque to open and close the valve. They usually use for high viscosity and high-pressure applications.
  4. Pneumatic: This method is also utilized in precision applications. This method uses compressed air to operate the valve.

Construction Materials of Butterfly Valves

Following are the most common materials used for the construction of the butterfly valve:

  1. Stainless steel: It is a steel alloy. It has a high chromium content of up to 10.5-30%. Stainless steel is best suitable for butterfly valves because it has high toughness and strength. Stainless steel has the ability to resist weather and corrosion. 
  2. Carbon steel: Carbon steel is also an alloy of steel. It contains carbon up to 2.5%. Carbon steel valves have low costs than stainless steel butterfly valves.
  3. Hastelloy: It is an alloy of molybdenum, chromium, and nickel. This material has the capacity to bear high temperatures and resist oxidizing, cracking, and corrosion. It has high strength. Hastelloy butterfly valves are best appropriate to control sulfuric, hydrochloric, and nitric acids at moderate temperature. 
  4. Brass: This is an alloy of zinc and copper. Brass is very durable and tough. It has the ability to bear high temperature. These butterfly valves are usually employed in pharmaceutical manufacturing, food, wastewater treatment, and water purification.
  5. Nickel Alloy: These alloys have high corrosion resistance. They have the capability to bear high temperature and bad weather conditions. Nickel alloy butterfly valves have more costs than stainless steel alloys.
  6. Titanium Alloy: It has a high strength-to-weight ratio. These valves typically use in water treatment applications and seawater environments. They also have very high costs.
  7. Nickel Aluminum Bronze: This material is a copper-based alloy that comprises 5% iron, 5% nickel, and 10% aluminum. These valves are used in wastewater treatment, water purification, and seawater environments.
  8. PVC: Polyvinyl Chloride is a rigid and tough material. This material valve usually uses for valves, fittings, and pipes. PVC butterfly valves are highly durable and corrosion-resistant. 

Advantages and Disadvantages of Butterfly Valves

Advantages of Butterfly Valve

  • They have small in size and lightweight than globe valves and ball valves.
  • These valves have a low price as compared to ball valves.
  • The butterfly valve requires a low installation area. 
  • They have an easy and quick operation.  
  • These valves are used to open, close or regulate the fluid flow.  
  • The valve disk has a low weight as compared to ball valves.
  • These valves require very low maintenance.
  • These are very precise due to that they are employed in different industries.
  • These have high-pressure recovery and low-pressure loss.
  • The butterfly valve has a compact design.
  • It requires much less structural support than ball valves of the same diameter.
  • A specific portion of the disk always faces the flow even when it fully opens. Therefore, regardless of the setting, the operation of the butterfly valve always changes the valve pressure.

Disadvantages of Butterfly Valve

  • The butterfly valves cant deliver an excellent sealing as ball valves.
  • The use of butterfly valve throttling is limited to systems with low-pressure drops.
  • The valve disk always presents in the flow even in the fully open condition; due to that, it increases the pressure drop.
  • The movement of the valve disk is guided and influenced by turbulence.

Applications of Butterfly Valve

  1. Municipal engineering
  2. Building water pipelines
  3. Environmental protection
  4. Hydropower applications
  5. Chemical and food industries
  6. Wastewater treatment
  7. Water purification

Difference between Ball Valve and Butterfly Valve

Ball ValveButterfly Valve
The ball valves have a high cost than butterfly valves.The butterfly valves have a low cost.
It has a high weight.It has a small size than ball valves.
It has large size.It has a small size.
These valves require more installation space than butterfly valves.These valves require less space for installation.
These provide a more perfect seal than butterfly valves.The butterfly valve doesn’t provide perfect seal-like ball valves.
Ball valves require more maintenance cost.These require less maintenance cost than ball valves.
The ball valves are more expansive than butterfly valves.It has a low cost.

FAQ Section

What is the function of a butterfly valve?

The main function of the butterfly valve is to close, open or slow the fluid flow. It uses to control the fluid flow in either direction.

What are the types of the Butterfly valve?

The butterfly valve has the following types:

  1. Rotary valve
  2. Concentric valve
  3. Lug-style valve
  4. Wafer valve
  5. Eccentric valve

What are the components of the Butterfly valve?

The butterfly valve has the following components:

  1. Body
  2. Stem
  3. Bushing
  4. Stem sealing 
  5. Handwheel
  6. Pins
  7. Disk
  8. Bolt thread
  9. Seat

What are the characteristics of the Butterfly valve?

  1. The butterfly valve has light weight than the ball valve.
  2. It requires very small installation space.
  3. It needs less structural support than the ball valve.
  4. The butterfly valves have a low cost.
  5. These valves require very low maintenance.

What is a ball valve used for?

A ball valve is a shut-off valve that uses to control the fluid flow by means of a rotary ball having a bore. By rotating the ball a quarter turn (90 degrees) around its axis, the medium can flow through or is blocked.

Read More
  1. Different types of Valves
  2. Working and types of Check Valves
  3. Types of Ball Valves
  4. Working of Plug Valve
  5. Working of Diaphragm Valve
  6. Types and working of Gate Valve

Leave a Comment