Butterfly Valves: Uses, Types, Working, Advantages, Symbols

Butterfly valves belong to quarter-turn rotational motion valves family and used primarily to stop, regulate, or start the flow. The term “butterfly” in a butterfly valve is actually a disk that is connected to a rod. When this rod rotates the disk by 90° the butterfly valve opens or closes. Butterfly valves are popular in industry because of their lightweight, fast operation, and low costs. These valves use handles, gears, or automatic actuators for operation as per the requirement.

Butterfly Valve Uses

The use of Butterfly valves is broad and wide. Some typical applications of butterfly valves are

• Water supply
• Wastewater treatment, Slurry services.
• Fire protection, air and gas supply
• Vacuum services
• Lubrication System
• In the chemical and oil industries
• In fuel handling systems
• Power generation
• Compressed air and gas services
• Steam Services
• Food Processing
• Pharmaceutical
• Marine System
• Sanitary Valve Application.

Basically, Butterfly Valves are suitable for use in

• Constant Load Applications
• Space-Restrictive Applications
• Throttling Valves

Components of a Butterfly Valve

There are four main components in a butterfly valve: body, disk, stem and seat.

• Valve body: the body of the Butterfly valves fits two pipe flanges, the most common body design is lug and wafer type (Fig. 2).
• Butterfly valve disk: The disk (disc) is the element that stops the flow. For improving flow, sealing, and operating torque, There are variations in disk design and orientation.
• Valve Stem: The stem of the butterfly valve consists of a one-piece or two-piece shaft design. Stem design shall prevent galling potential between similar corrosion-resistant materials.
• Butterfly valve Seat: To provide shutoff, the seat of a butterfly valve utilizes an interference fit between the disk edge and the seat. The seat may be bonded, pressed, or locked into the body.

Functions of a Butterfly Valve

The main functions of a butterfly valve is

• Flow regulation: Flow can be easily controlled or regulated simply by turning the valve wheel.Using a flow controller the process can be automated.
• Flow Isolation
• Prevention of Backflow: Butterfly valves can be used for backflow prevention in some situations.

Types of Butterfly Valves

Depending on disc closure design, connection design, and actuation method, Butterfly valves can be categorized into several types.

• Based on Disc Closure Design
  • Concentric Butterfly Valve
  • Eccentric Butterfly Valve
    • Single-Offset
    • Double Offset
    • Triple Offset
• Based in Piping Connection
  • Lug type
  • Wafer Type
  • Flanged Butterfly Valve
  • Butt-welded Butterfly Valves for high-pressure applications
• Based on Operation method
  • Manual Actuation
    • Lever Operated
    • Gear Operated
  • Automatic Actuation
    • Electric
    • Pneumatic
    • Hydraulic
• Based on Seat Material
  • Soft Seated
  • Metal Seated

Concentric Butterfly Valve

The concentric butterfly valve is the most basic type of butterfly valve design. In this design, the stem passes through the centreline of the disc. This is also known as a zero-offset valve. Concentric butterfly valves are used for low-pressure services.

Eccentric Butterfly Valve

In an eccentric butterfly valve, the stem does not pass through the centerline of the disc. There are three types of offset valves.

• A Single-offset valve is the butterfly valve where the stem is located right behind the centreline of the disc.
• In a double-offset butterfly valve design, the stem is located behind the disc with an additional offset to one side.
• For highly critical applications, a triple offset butterfly valve is used. The third offset is in between the disc and seat contact axis. This design results in minimal seat contact thus very less wear and highly efficient.

Lug Type Butterfly valve

The lug-style butterfly valve (Fig. 2) designs have threaded lugs outside the valve body. Using two sets of studs, the valve is connected with piping flanges. One end of the line can be disconnected without affecting the other side since each flange has its own bolts.

Wafer Type Butterfly Valve

A wafer-type butterfly valve is sandwiched between two pipe flanges and the flange bolts surround the valve body. This is the most economical butterfly valve. Long bolts are used covering both flanges and valve body. A wafer butterfly valve provides sealing against bi-directional pressure difference in the fluid flow. The wafer version of the butterfly valves is designed to protect against a tight seal and two-way pressure difference.

Butterfly Valve Advantages

Butterfly Valves provides many advantages as compared to other valve types.

• Compact design; little space requirement.
• Lightweight; easily supported by the piping system.
• Quick operation; less opening or closing time.
• Easy to Install.
• Simple operation due to low operation torque.
• Available in very large sizes
• Improved energy efficiency
• Low-pressure drop and high-pressure recovery
• Long valve life
• Relatively inexpensive to build.
• Less number of parts; Hence, reduced maintenance.

Disadvantages of Butterfly valve

However, there are few disadvantages of butterfly valve as listed below

• Throttling service is limited to low differential pressure
• Disc movement is affected by flow turbulence.
• The valve disc is always under pressure and can interrupt the flow even in an open position.
• Possibility of Cavitation and choked flow is a concern
• Poor Sealing function.
• Not suitable for high differential pressure.

Butterfly Valve vs Gate Valve

The main differences between a butterfly valve and a gate valve are tabulated below

Butterfly Valve	Gate Valve
Obstructed flow even in a fully open position	Unobstructed flow in the fully open position
Easy to handle and install	Comparatively difficult
Size smaller, reduced space requirements	Size bigger, more space requirement
Comparatively less pressure withstanding capability	High pressure withstanding Capability
Quick operation, possibility of water hammer	Operating time is more; less chance of surge.
Shorter Shaft, Easy access	Longer Shaft, difficulty access
Less weight	More weight
Cheaper	Expensive

Ball Valve vs Butterfly Valve

The main differences between butterfly valve and ball valve is produced below in a tabular format.

Butterfly Valve	Ball Valve
Disk Mounted	Ball Mounted
More Pressure drop	Less pressure Drop
Less sealing	More effective Sealing
Light Weight	Heavier
Less Space	More Space
Cheaper	Costly

Symbol of Butterfly Valve

The following symbols are used as butterfly valve symbol in isometric and P&ID.

Butterfly Valve Standard

Industrial Butterfly valves are designed based on the following butterfly valve standards

• API 609
• MSS SP-67
• BS EN 593
• ISO 5752
• MSS SP-68
• AWWA C504

Butterfly Valve Materials

The following materials are normally used for butterfly valve components

Butterfly Valve Body	Disc Material	Stem material	Seat material
Carbon Steel	Aluminium	Cast Steel	Neoprene
Stainless Steel	Stainless Steel	Stainless Steel	PTFE
Cart Iron			EPDM
Ductile iron			NBR
Cast Bronze			Viton
DSS			BUNA-N
Nickel Alloy/Hastelloy			Inconel (Metal Seat)
Titanium Alloy			Stainless Steel

Data to be Provided for Butterfly Valve Manufacturer

The following data should be provided to the butterfly valve manufacturer while ordering

• Flange rating/Pressure
• Specific gravity, viscosity, material content, the composition of the fluid to be handled.
• Pressure drop or required Cv (maximum)
• Flow rate
• Design and operating temperatures
• Piping moments
• Valve body, Disc, Seat material
• Valve plate material
• Valve diameter or connected pipe diameter

Butterfly Valve Working Principle

The butterfly valve operates based on the quick shut off principle. The circular disc (butterfly) 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. Using the handwheel, the metal disc is rotated to keep the disc parallel or perpendicular to the flow and it allows or closes the flow. So, the operating principle of the butterfly valves is fairly simple. The animation below by the GEMU group clearly shows the butterfly valve working.

Butterfly Valve Manufacturers

There are many butterfly manufacturers in this world. List of a few of the world-renowned butterfly manufacturers are provided below:

• Dezurik
• Pentair Valves and Controls
• Flowserve Corporation
• Fisher Valves
• Flomatic Valves
• Crane Company
• NIBCO
• Bray Valves
• Zwick
• Kitz Corporation
• Hobbs Valve
• Apollo Valves
• Kieselmann
• Valworx
• Davis
• Velan
• Emerson Electric Company
• L&T Valves
• Cameron
• Amco Industrial Valves
• VIP Valves