Manual Butterfly Valve

What is a manual butterfly valve? 

This is a butterfly valve that is operated using a handwheel or hand lever. A valve operator is needed to start and stop the valve. This valve works by turning the handle which then turns the disc so that it can open or close the fluid flow as necessary. The opening and closing operations need only a quarter turn of the handle a feature that makes these valves quick in operation. These valves are cheaper compared to automatic ones. Manual butterfly valve manufacturers produce this valve using different materials. These materials determine where the valve can be used in terms of temperature and type of fluid that is, corrosive or non-corrosive to viscous fluids. Manual butterfly valves are designed with short lengths which makes them occupy small space relative to other valves. Also, this helps to reduce the weight and cost of the valve. These valves are designed to allow bi-directional fluid flow although there are few of them meant for unidirectional fluid flow. 

Figure: Manual butterfly valves.

Components of a manual butterfly valve 

Handwheel/hand lever 

This is the part of a manual butterfly valve where the operator applies force to start or stop fluid flow. Some of the valves are designed to operate using a handwheel while others use a hand lever. 

Body 

The body is the main component that houses the internal parts. Manual butterfly valve manufacturer design the body using strong metallic materials such as stainless steel, carbon steel, nickel alloys, and brass among other strong materials. These materials make the body very strong enough to withstand the weight of other components. The high strength also helps the valve withstand fluid pressure as well as protect internal components against falling objects. 

Stem 

The stem is the part that connects the handwheel/ hand lever to the disc. This component of manual butterfly valve is used to transmit power from the handwheel to the disc. The stem is also made of metallic material to help withstand the torque needed to open and close the valve. 

Gear box

This is a component that houses gears used in some manual butterfly valve to change direction of torque from horizontal to vertical. This happens where the handwheel is oriented perpendicular to the stem. The gear box is mounted on top of the valve stem.

Disc 

This is the component that is responsible for opening and closing fluid flow through the valve. The disc gets the power to operate from the handwheel through the stem. 

Seats

This is a component placed between the disc and the valve body. Seats serve as the surfaces on which the disc rests when the valve is closed. Manual butterfly valve manufacturers design these valves with two seats. The work of the seats is to prevent fluid leakage when the valve is closed.

Gasket 

This is a component placed between the valve and pipe connection to prevent fluid leakage. Manual butterfly valve manufacturers design the gasket from various materials. The material used to make the gasket determines where that valve can be used. 

Figure: Components of manual butterfly valve.

How does a manual butterfly valve work? 

A manual butterfly valve operates when the operator applies torque on the handwheel or hand lever. This helps to either close or open the fluid flow. To open the valve, the handwheel/ hand lever is turned in the counterclockwise direction. This torque is then transmitted to the valve disc through the stem. The disc then makes a quarter turn angle where it aligns itself parallel to the fluid flow leaving the valve open. The fluid then keeps flowing through the open valve. To close the valve, the handwheel/ hand lever is rotated in the clockwise direction for another quarter turn. This torque returns the disc to the seating position. In this position, the disc becomes perpendicular to the fluid flow direction where it blocks any fluid attempting to cross the valve. For throttling fluid flow, the operator turns the handwheel/ hand lever to a certain angle of less than 90^o degrees which forces the disc to open slightly allowing some amount of fluid to cross the valve. 

Figure: Working of a manual butterfly valve.

Types of Manual butterfly valves 

Concentric manual butterfly valve 

This valve is also known as a zero-offset manual butterfly valve. This is the most basic type of a manual butterfly valve. Manual butterfly valve manufacturers design this valve such that the stem centerline is collinear to the disc centerline. The disc is placed at the center of the pipe diameter while the seat is in the periphery of the valve body. The disc and seat remain in constant contact. Manual butterfly valve manufacturers design these valves with soft seats that is seats made of plastic or rubber materials. The flexibility of the seat makes the valve to efficiently seal fluid flow when the valve is stopped. Due to the soft seats, this concentric butterfly valve is suitable for use only in low-pressure and low-temperature applications below 60 ^oC. The media flowing through this valve does not come into contact with the valve body because the seat is made as a sleeve inside the valve body. 

Figure: Concentric manual butterfly valve.

Eccentric manual butterfly valve

This valve is also known as a high performance butterfly valve. This valve has the stem passing some distance from the disc centerline. From this design, two types of valves are the double offset type and the triple offset type. 

1. Double offset manual butterfly valve. This type has the stem axis offset behind the seat centerline and valve body which forms the first offset. The second offset is produced by having the stem offset from the vertical centerline of the valve body. When the valve is started, the seat lifts from the seal which then reduces friction for the first and last 10^o degrees of the valve start and stop respectively. Manual butterfly valve manufacturers use this design to enhance smooth operation and tight shut-off. This design also enhances longer life span of the valve relative to the concentric manual butterfly valve. These valves are designed with soft seats which makes them suitable for moderate pressure and low temperatures. For this valve to be used at a higher temperature, the disc is coated with a layer of metallic material. Double offset butterfly valves are used in applications such as HVAC, wastewater treatment, and fire protection among others. 

2. Triple offset manual butterfly valve. This type of eccentric valve has three offsets. The first two are the same as that of a double offset valve while the third one is a cone axis of the body seal. The third offset is accomplished by use of a right-angled cone profile of the valve seat and a matching profile at the edge of the disc. The use of a third offset helps to reduce disc and seat contact when the valve is closing or opening which then reduces friction. Contact happens when the valve is fully closed. Manual butterfly valve manufacturer design this valve with metal seats. Metallic seats are more rigid and tough relative to rubber or plastic seats. As such, this valve can operate at high temperatures and high pressure. The use of metal seats also helps to reduce wear on the internal parts. Triple offset butterfly valve have long service life relative to the double and the concentric valve types. Manual butterfly valve manufacturers design this valve to work in harsh applications such as corrosive chemicals, superheated steam, high-temperature gases, and liquids among other applications where other manual butterfly valves cannot be used. 

Butt-weld manual butterfly valve 

 This is a manual butterfly valve that is welded to the pipe. This type of valve is used where the piping system is transporting hazardous fluids like corrosives and flammable products. Manual butterfly valve manufacturers design this valve for use where frequent operation is not expected. Also, this valve is suitable for use where high levels of hygiene are not expected since the valve cannot be opened for cleaning while in the field. In case the valve needs some repairs, the weld has to be removed first. These valves guarantee leakage proof between the valve and the pipe which ensures no injuries to the valve operator or to the environment which may happen in other valves that use bolts. 

Applications of manual butterfly valves

• Manual butterfly valves are used in petroleum refinery. 
• They are used in heating, ventilation, and air-conditioning (HVAC). 
• They are used in steam power plants to control the flow of water and steam into and out of boilers. 
• Manual butterfly valves are used in mining industries. 
• They are used in the manufacturing of various types of chemicals. 
• These valves are used in municipal water purification and wastewater treatment. 
• Manual butterfly valves are used in food processing because of their ease to clean to enhance hygiene.      
• These valves are used in oil and gas processing and offshore pipelines.
• Manual butterfly valves are used in the manufacturing of paper and pulp. 
• These valves are used in fire protection. 

Advantages of manual butterfly valves 

• Manual butterfly valves are cheaper compared to automatic types. 
• They are simple and compact in design. 
• They need a quarter turn to open and close which saves time and energy. 
• Manual butterfly valves are lightweight relative to other valves. 
• They serve well in areas with limited space due to their small size relative to other valves. 
• They can be bi-directional or uni-directional.
• Manual butterfly valves are easy to install, repair, and clean. 
• They are versatile for use in different industries. 
• Manual butterfly valves can be used for shut-off or throttling flow. 

Disadvantages of manual butterfly valves 

• These valves open with the disc in the fluid flow path which reduces fluid pressure.
• Manual butterfly valves may be tedious where high torque or frequent operation is needed. 
• These valves have seals that are weak compared to other valves like ball valves. 
• Manual butterfly valves are prone to cavitation and choking. 

Troubleshooting manual butterfly valves 

Valve is hard to operate 

• Solid particles clogged in the valve. Open the valve and remove the solid particles. 
• Disc and or stem are corroded. Open the valve and remove the corrosion. Clean inside of the valve. 

Fluid leakage when the valve is closed

• Dirt inside the valve. Open the valve and clean the dirt. 
• Worn out seats. Replace the seats. 
• Worn out disc. Repair or replace the disc as necessary. 
• Worn out O-rings. Replace the O-rings. 

Fluid leakage between the valve and pipe 

• Loose bolts. Tighten bolts to the torque recommended by the manual butterfly valve manufacturer. 
• High fluid pressure. Verify the fluid pressure level is as recommended by the manual butterfly valve manufacturer. 

Summary 

A manual butterfly valve is a valve that is operated manually. This valve is operated by use of a valve handwheel or hand lever. The handwheel or hand lever is where the operator applies torque to start or stop the valve. Manual butterfly valve manufacturers design this valve to operate by making a quarter turn angle. The operator turns the handle for a 90^o degree angle in the counterclockwise direction to open fluid flow. The handle is rotated in the opposite direction for another quarter turn to close the fluid flow. This valve is also used in throttling fluid flow in which the operator turns the handle for an angle of less than 90^o degrees. 

Manual butterfly valve manufacturers produce various types of these valves which include concentric manual butterfly valves, eccentric manual butterfly valves, and butt-weld manual butterfly valves among others. Areas of application of these valves include fire protection, mining, water supply, paper and pulp, steam power plants, chemicals, and food processing among others. Advantages of purchasing manual butterfly valves include less expensive, quick operation, small installation space, small in size and light in weight, simple and compact design, and easy to clean, install and repair.