Lug Butterfly Valve

What is a lug butterfly valve? 

This is a valve designed with threaded lugs outside the body. These threaded lugs are used to contain bolts used to connect the valve to the pipeline. This type of valve is installed into the piping system by placing it in between two pipe flanges. A tight seal is enhanced by mounting a gasket between the mating surfaces of the valve and the pipe plus the bolts. Two separate bolt sets are used on each end of the valve without the use of nuts. This design makes the valve work as an isolation valve or makes it suitable for installation in the end-of-line service. Such design makes it easy to dismantle one end of the valve without disturbing the other end which helps to reduce downtime when doing repair and maintenance. Lug butterfly valve manufacturers design this type of valve with short lengths making it economical relative to other valves. Also, this short length helps the bolts to extend from one pipe flange to the other flange across the lug-style butterfly valve. The challenge of these valves is that they carry the pipeline weight thus the valve body has to be strong. 

Figure: Lug style butterfly valve.

Components of a lug-style butterfly valve 

Valve body 

This is an external component of a lug-style butterfly valve that is used to house internal parts. The body is made very strong to help it withstand fluid pressure. As such, lug butterfly valve manufacturers use strong materials like carbon steel, ductile iron, and stainless steel to make this component. However, a special case is when the valve is made of fully plastic material for use in corrosive media and at low temperatures below 60 ^oC.

Handwheel/actuator 

This is the component of a lug-style butterfly valve used to provide the force needed to open and close the valve. The handwheel or hand lever is used in manual lug butterfly valves while the actuator is used in automatic and semi-automatic types. 

Stem 

This component connects the valve disc to the handwheel/actuator. The stem serves to transmit force applied on the handwheel to the valve disc. 

Disc 

This is the component tasked with opening and closing fluid flow. The disc gets its power to work from the handwheel/actuator through the stem. 

Seats 

Lug-style butterfly valves have two seats. The seats provide the surface where the disc rests when the valve closes. The seats also ensure no fluid leakage when the valve is closed as they enhance a bubble-tight seal together with the valve disc. 

Gasket 

This part is placed between the pipe and valves mating surface to prevent any fluid leakage. 

Figure: Components of a lug butterfly valve.

How does a lug butterfly valve work? 

A lug-style butterfly valve is classified as a quarter-turn valve. A quarter turn valve is a valve that operates by turning the valve disc at 90^o degree angle. This helps to either open or close the fluid flow path. These valves are either manual or actuated. The working mechanism is the same for both manual and actuated types. To start a lug-style butterfly valve the valve operator turns the handwheel for a quarter turn. This rotary motion is transmitted to the valve disc via the valve stem. This makes the disc make the same quarter turn where it becomes parallel to the fluid flow direction and where it leaves the flow path open. The fluid keeps flowing through the lug butterfly valve provided the disc is kept open. To close fluid flow, the valve operator turns the handwheel in the clockwise direction where the disc turns to be perpendicular to the fluid flow direction. This ensures fluid flow through the valve is blocked. These valves are also used in throttling applications where the disc is turned to a slight angle to allow some amount of fluid flow through the valve. 

Figure: Working of a lug style butterfly valve.

Types of lug butterfly valves 

Manual lug butterfly valves 

This is the type of a lug butterfly valve that is operated manually by the use of a handwheel or hand lever. The valve operator operates the valve by applying force on the handwheel or hand lever to make the valve disc open or close as necessary. Lug butterfly valve manufacturer design these valves such that in case it becomes necessary they can be automated in the future. These valves are cheaper compared to the actuated ones. These valves are easy to operate as the operator only needs to turn the handwheel for a quarter turn to allow or block fluid flow. However, in some applications, the torque needed to operate the valve may be too high for the operator causing a lot of fatigue, especially where the valve operation is very frequent. 

Figure: Manual lug butterfly valve.

Pneumatic lug butterfly valve 

This is the type of a lug-style butterfly valve that operates using a pneumatic actuator. This is the actuator that operates by using compressed air. The compressed air is responsible for providing the torque that works to open and close the valve. Lug butterfly valve manufacturers design these valves for use in different applications such as sanitary and other applications that need high levels of hygiene. This is because the compressed air used can be cleaned making it hard to cause any contamination to the fluid or media being transported. These valves can also be used in high-temperature applications depending on the materials used to make the whole or parts of the valve. 

Figure: Pneumatic lug butterfly valve.

Electric lug butterfly valve 

This is a lug butterfly valve that operates using an electrical actuator. The actuator consists of an electrical motor that helps to convert electrical energy to mechanical energy. The mechanical energy is in terms of rotary speed and torque which is then passed through a speed reduction system to reduce the motor speed. Electric lug butterfly valves are automated such that they can close and open independently without involvement of the valve operator. Lug butterfly valve manufacturers also make these valves with a control mechanism that makes it possible to remote control their operations. Electric lug-style butterfly valves are versatile as they can be used in all applications due to availability of electricity. These valves can be used in different types of media and in a wide range of temperatures depending on the material used to make the valve. 

Figure: Electric lug butterfly valve.

Hydraulic lug butterfly valve 

This is a lug-style butterfly valve that operates using hydraulic actuator and fluid. The hydraulic actuator is a device that controls fluid flow through a hydraulic circuit. This type of valve is very powerful since it uses incompressible fluids. This makes the valve produce high values of torque. Lug butterfly valve manufacturers design this valve for use in applications that involve shut-off and throttling of fluid flow. This valve is made of strong materials as it is used in high-pressure applications. Advantages of using these valves include large torque and adjustable torque and smooth and reliable smooth operation. 

Figure: Hydraulic lug butterfly valve.

Plastic lug butterfly valve 

This is a lug-style butterfly valve that is made of fully plastic material. Lug butterfly valve manufacturers make these valves with plastic materials for use in low-temperature applications that are below 60 ^oC. If used at temperatures above this limit the valve will melt down and thus be not useful again. These valves are suitable for applications that involve highly corrosive fluids such as acids since plastic materials are very resistant to corrosion than metallic materials. Plastic lug butterfly valves are cheaper than the metallic counterparts. These valves are also light in weight compared to the metallic types. However, the material used to make this valve must guarantee high strength which ensures the valve can withstand fluid pressure as well as the weight of the valve components. One of the commonly used plastic materials used to make these valves is polyvinyl chloride. This material has high strength which protects the valve against impact damage and fluid pressure. 

Figure: Plastic lug butterfly valve.

Applications of lug-style butterfly valves 

• Mining operations. 
• Chemical manufacturing plants. 
• Water purification and treatment applications. 
• Boiler applications to control the flow of steam. 
• Paper and pulp manufacturing industries. 
• Foods and beverages industries because of their ease to clean to enhance high levels of hygiene. 
• They are used in applications involving slurries and sludge.

Advantages of lug butterfly valves 

• Can be automatic or manual depending on the customer’s preferences and the area of application. 
• These valves make a quick turn to open and close which makes them fast operating. 
• Versatile because they can be used in different industrial applications ranging from low to high temperature and corrosive to non-corrosive based on the material used to make the valve. 
• Simple and compact design and light in weight. 
• Cheaper compared to other valves like gate valve. 
• They occupy small installation space due to their small sizes. 
• They can be used as shut-off and throttling valves. 
• Slurry applications as they hardly get clogged. 
• Easy to install, clean, and repair.

Disadvantages of lug-style butterfly valves 

• These valves do not have excellent seal compared to other valves like ball valve. 
• The valve disc is influenced and guided by fluid turbulence.
• These valves are only suitable for use in throttling applications if there is a low-pressure drop. 
• The lug-style butterfly valve has the valve disc in the flow area when the valve is open which increases pressure drop. 

Troubleshooting lug style butterfly valve 

External fluid leakage 

• Loose pipe-valve connection. Tighten the valve bolts to attain the torque recommended by the lug butterfly valve manufacturer. 
• Worn-out O-rings. Replace the O-rings. 
• Worn out packing. Replace the valve packing to prevent leakage between the stem and the valve body. 
• Worn out or damaged gasket. Replace the gasket. 

Internal fluid leakage 

• Worn out O-rings. Replace the O-rings.
• Damaged seat. Replace the seats.
• Clogged materials in the valve. Open the valve and remove any clogged materials. Clean the interior of the valve. 

Valve is hard to operate  

• Foreign materials blocked the valve. Open the valve and remove any foreign materials. 
• Loose actuator. Tighten the bolts connecting the valve and actuator. 
• Corrosion on the actuator components. Clean off corrosion. 

Summary 

A lug-style butterfly valve is a type of quarter-turn valve. This valve operates by making a quarter turn angle to open or close the fluid flow. Lug butterfly valve manufacturers design this valve with threaded lugs outside the valve body. These lugs are meant to hold bolts that are used to connect the pipe and the valve.

The valve is installed between two pipeline flanges using the bolts. A gasket is placed between the valve and pipe mating surfaces to prevent fluid leakage. The valve body is usually designed to have short lengths which makes it easy to connect the bolts from one pipe end to the other end. This also makes the valve body small in size and light in weight. As such, lug-style butterfly valves end up being cheaper compared to other valves.