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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 90o 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.
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
Advantages of manual butterfly valves
Disadvantages of manual butterfly valves
Troubleshooting manual butterfly valves
Valve is hard to operate
Fluid leakage when the valve is closed
Fluid leakage between the valve and pipe
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 90o 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 90o 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.