Lug Type Butterfly Valve

What is lug type of butterfly valve? 

This is a valve designed with lugs that have threads on the valve body flanges. Lug type butterfly valve is connected to the pipe using bolts. The bolts are inserted through the threaded lugs. Lug butterfly valve manufacturers use this design so that it is easy to disconnect one end without affecting the other end. Lug-type butterfly valves operate using a handwheel or actuator. The operation of the valve is based on a quarter turn of the handwheel or actuator to open or close fluid flow as necessary. Lug-type butterfly valve manufacturer design these valves using different materials on different components of the valves. The material used to make the valve determines where the valve can be used as well as the operating temperature. Some of the lug-type butterfly valves are designed to allow bi-directional fluid flow while others allow fluid flow in one direction only. 

Figure: Lug type butterfly valve.

Components of a lug-type butterfly valve 

Body 

This is the part of a lug-type butterfly valve that is used to hold all other parts together. The body is made of metallic materials to make it very strong. Some of the strong metallic materials used to make the body include titanium alloy, stainless steel, brass, and carbon steel among others. The body is designed with lugs that have holes to hold the bolts used to connect the valve and pipe together. 

Actuator/handwheel 

This refers to the component used to provide the torque needed to turn the valve to start and stop fluid flow. The actuator is used where the valve is automatic or semi-automatic while the handwheel or lever is used in manual lug butterfly valve. The handwheel is where the valve operator applies torque to open or close the valve. 

Stem 

This is the component of a lug-type butterfly valve that connects the handwheel/actuator to the valve disc. The stem helps transmit torque from the handwheel to the disc. This torque helps to turn the disc 90^o degrees to open or close the fluid flow. 

Disc 

This is the part of a lug-type butterfly valve that is used to start and stop fluid flow. The disc is connected to the handwheel/actuator through the valve stem. 

Seat

This is the component of a lug-type butterfly valve that helps to prevent fluid leakage when the valve is closed. The seat provides the surface where the valve disc rests when the valve stops. The seat material can be soft or metallic. Soft seats are meant for use in low temperatures while metallic ones are used in high temperatures applications.

Gaskets 

This is a component placed between the valve and pipe mating surfaces to prevent fluid leakage. The gasket is held in its place after the valve and pipe are connected using bolts.

Figure: Components of a lug type butterfly valve.

How does a lug-type butterfly valve work? 

A lug-type butterfly valve is a quarter-turn valve. This means that the valve disc makes a quarter turn angle to open or close fluid flow. To open a lug-type butterfly valve the handle is rotated in the anticlockwise direction for a quarter turn that is 90^o degree angle. The torque applied on the handle is transmitted to the valve disc through the valve stem. This torque makes the valve disc to turn and become parallel to the fluid flow direction. This condition leaves the valve open allowing fluid to flow through the valve. To stop the fluid flow, the handle is again rotated for a quarter but in the opposite direction (clockwise direction). This rotation makes the disc turn to become perpendicular to the fluid flow. The orientation of the disc perpendicular to the fluid flow ensures the fluid flow path is blocked hence no fluid can flow through the valve. Lug-type butterfly valve manufacturers design this valve such that it can be used for both shut-off and throttling applications. For throttling fluid flow, the handle is turned slightly allowing the disc to turn to allow slight fluid flow.

Figure: Working of a lug type butterfly valve.

Types of lug type butterfly valves 

Manual lug type butterfly valve 

This is a manual lug-type butterfly valve that is operated manually using a handwheel or hand lever. This type of valve is cheaper compared to the actuated ones. Manual lug-type butterfly valve manufacturers design this valve such that it can be automated in the future if it becomes necessary. The working of this valve requires the application of torque on the handle by the valve operator to start or stop fluid flow. This type of valve is suitable for use in medium and small-sized valves since large lug-type butterfly valves need a lot of torque to open. Manual butterfly valves are versatile as they can work even where there is no electricity. However, this type of valve poses danger to the valve operator especially if the media being transferred is hazardous like flammable fluids such as oil and gas or corrosives like acids. This is because any leakage when the valve operator is working on the valve can cause injuries or death. 

Figure: Manual lug type butterfly valve.

Plastic lug type butterfly valve 

This is a lug-type butterfly valve that is made of plastic materials. Lug-type butterfly valve manufacturers design this valve for use in low-temperature applications that is below 60 ^oC. This is because plastic materials do melt or get deformed by high temperatures. However, these valves have excellent resistance to corrosive media like acids. As such, lug-type butterfly valve manufacturers recommend use of these valves where the temperature is low but where the media is very corrosive. Also, these valve can be used in non-corrosive media like fresh water since they are cheaper compared to the metallic ones. Another good property of the plastic lug-type butterfly valve is that it is light in weight due to the low density of plastic materials. Polyvinyl and propylene are some of the plastic materials that are used to make these valves. 

Figure:Plastic lug type butterfly valve.

Hydraulic lug type butterfly valve 

This is a lug-type butterfly valve that is operated using the hydraulic actuator. The actuator used is operated using hydraulic fluid. Lug-type butterfly valve manufacturers design the actuator with an automated system that determines when the valve can be opened. This type of valve can also be remote controlled via the automated system. Hydraulic lug type butterfly valve produces high torque due to incompressibility of hydraulic fluid. This makes the valve suitable for use in lug-type butterfly valves that need a lot of torque. 

Pneumatic lug type butterfly valve 

This is a lug-type butterfly valve that operates using compressed air. Pneumatic butterfly valve manufacturers recommend the use of this valve, especially in those applications that need high levels of hygiene because the compressed air can be filtered to ensure zero contamination. This type of valve operates by using compressed air mechanism to rotate the valve stem which then rotates the valve disc to open and close the fluid flow. Pneumatic lug-type butterfly valves like other actuated valves are designed with a control system that determines when the valve closes and opens. These valves are reliable and durable if used according to the lug-type butterfly valve manufacturer’s instructions. 

Electric lug type butterfly valve

This is a lug-type butterfly valve that is operated using electrical power. The electrical power is converted into mechanical energy using an electric motor and speed reduction system. This mechanical energy is responsible for the torque used to start and stop the valve. This type of valve can be used in almost all areas of valve applications due to the availability of electricity. However, when there is a power failure the valve will be able to start or stop thus the valve would stall. Lug-type  electric butterfly valve manufacturers design these valves with a control system that determines when to start or stop. The automation of the control system can also be designed for remote control applications. 

Applications of lug-type butterfly valves 

• Wastewater treatment and water supply. 
• Chemical applications. 
• Paper and pulp manufacturing industries. 
• Refinery of petroleum products. 
• They are used in firefighting applications. 
• Steam power plant industries. 
• Oil and gas transportation. 
• These valves are used in food and beverage manufacturing. 
• Applications involving slurries and sludge as they hardly get clogged.

Advantages of lug-type butterfly valves 

• Small in size and light in weight. 
• They are of simple and compact design. 
• Used for both shut-off and throttling applications. 
• They can be operated manually or actuated depending on the customer’s preferences. 
• valves can be used in both low and high temperatures depending on the material used to make the valve or internal parts. 
• These valves are easy to install, clean, and repair. 
• They open and close very fast. 
• Cheaper compared to other valves like gate valve and globe valve. 
• They occupy a small space when installed compared to other valves, such as ball valve. 

Disadvantages of lug-type butterfly valves 

• The disc in these valves is not guided and thus it is always affected by fluid turbulence. 
• The use of lug-type butterfly valves in throttling applications should only be in low-pressure applications. 
• Choked and cavitation flow are two main technical challenges associated with these valves. 
• When the valve is open, the disc remains in the fluid flow path which creates some level of fluid resistance thus reducing efficiency. 

Troubleshooting lug-type butterfly valves 

Internal fluid leakage 

• The valve seat is damaged or worn out. Replace the valve seat. 
• The disc is damaged or worn out. Replace the disc. 
• Disc is not firmly closed. Tighten the disc to become fully closed. 
• Foreign materials clogged in the valve. Open the valve and remove any foreign materials causing a blockage. 

External fluid leakage 

• Worn out or damaged gasket. Replace the gasket. 
• Loose connection between the valve and pipe. Tighten the bolts to enhance torque recommended by the lug-type butterfly valve manufacturer. 

The handle is hard to rotate 

• Materials clogged in the valve. Open the valve inside and remove any materials interfering with the valve opening or closure. 
• Corrosion in the valve. Check the valve for any corroded material and clean off the corrosion. 

Summary 

A lug-type butterfly valve is a type of valve used for on and off as well as in throttling fluid applications. However, the use of this valve in throttling fluid flow is subject to limited fluid pressure. Lug-type butterfly valves are made of short length bodies which makes it easy to connect them to the pipe. The connection is done using bolts. This helps to enhance high strength against fluid pressure.

Lug-type butterfly valve manufacturers design the body with threaded lugs where the bolts are inserted. Lug-type butterfly valves operate by turning the disc for an angle of 90^o degrees. This makes the valve disc be oriented parallel to the fluid flow direction leaving an unobstructed path. The valve is closed when the disc is rotated via the handle to become perpendicular to the fluid flow direction.