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Gear Operated Butterfly Valve

June 25, 2022

What is gear operated butterfly valve?

This is a manual butterfly valve that uses gears to enhance torque multiplication. Gear-operated butterfly valves have the gear system connected to the handwheel through a short shaft. This allows the torque applied by the valve operator to go direct to the gear system. The torque is then multiplied through a system of gears which makes high torque-demanding butterfly valves easy to open. This makes it easy for the valve operator to open and close the fluid flow even when the valve is used in frequent and high torque applications. Gear-operated butterfly valve manufacturers design this type of valve for use in on and off as well as throttling applications. Gear-operated butterfly valves are in the category of quarter turn valves. These are valves that need only a 90^o degree turn of the handwheel to open or close. Also, such valves need a slight angle for throttling applications. Gear operated butterfly valves help to save time when opening and closing fluid flow unlike other valves like gate valves that need numerous turns to open and close. Gear-operated butterfly valve manufacturers employ simple designs when making these valves which makes them less expensive.

Figure: Gear operated butterfly valve.

Components of a gear-operated butterfly valve

Valve body

This is the component of gear operated butterfly valve that houses internal parts. This part is made of strong metallic materials like ductile iron, nickel alloys, stainless steel, and carbon steel among other materials. These materials are strong and thus they help to make a strong valve body. The high strength is necessary as it makes the valve withstand the weight of the whole valve and safe against impact damage from falling objects.

Handwheel

This is the component that is used by the valve operator to apply the torque required to open or close the valve. The handwheel is connected to the gear system via a short shaft.

Gear system/gear box

This is a mechanical system composed of gears that are in mesh. It is placed on top of the valve. These gears are meant to help in multiplying the torque applied on the handwheel by the valve operator. This system helps to make the torque needed to open or close the valve much less and thus reduce the workload on the valve operator.

Stem

This is a shaft component used to transmit torque applied by the valve operator to the valve disc. The stem connects the disc to the gear system. As such, it receives torque from this gear system.

Disc

This is the part of gear operated butterfly valve that is used to open and close the valve. The disc gets its power from the gear system via the stem.

Seat

This is the component that serves to provide a surface for the valve disc to rest on when the valve is closed. There are two seats used and which work together to ensure no fluid leakage when the valve closes.

Gasket

This part is placed between the pipe and valve mating faces to prevent fluid leakage.

Figure: Components of a gear-operated butterfly valve.

How a gear does a gear operated butterfly valve work?

A gear-operated butterfly valve operates by getting power from the valve operator. The operator applies force on the handwheel to operate the valve. The handwheel is connected to a gear system via a short shaft. To open the valve, the operator turns the handwheel for a quarter turn in the anticlockwise. This makes the torque (or rotary force) applied on the handwheel to be transmitted to the valve disc via the stem. As such, the disc makes a quarter turn angle where it becomes oriented parallel to the fluid flow. In this state of the disc, the fluid flows through the valve unobstructed. To close the fluid flow, the valve operator turns the handwheel in the clockwise direction. This forces the disc to make a 90_o degree turn and become perpendicular to the fluid flow. In this state, the disc blocks fluid flow crossing the valve. Gear-operated butterfly valve manufacturer make these valves for use even in throttling applications. However, the use of these valves in such throttling applications is recommended where the pressure drop is low. When the valve needs to be used in throttling applications, the valve operator turns the handwheel slightly for an angle of less 90^o degrees depending on the amount of fluid flow required.

Figure: Working of a gear operated butterfly valve.

Types of gear-operated butterfly valves

Double flange gear-operated butterfly valve

This is a gear operated butterfly valve designed with pair of flanges on the inlet and outlet ports. The valve is connected to two pipe ends with equal size of flanges as the valve. Two sets of bolts are used to hold the valve and pipe together ensuring zero leakage. Gear-operated butterfly valve manufacturers recommend these valves for use in high-pressure applications to make the piping system economical. These valves are made of soft seated or metallic seats depending on where they will be used. Double flanged butterfly valves are heavier compared to other butterfly valves. The high weight is due to the double metallic flanges and bolts and nuts used.

Figure: Double flange gear operated butterfly valve.

Gear-operated wafer butterfly valve

This valve is connected to the pipe by placing it between two pipe flanges. The pipe flanges and the valve are connected using long bolts that extend from one pipe end to the other end across the valve body. Gear-operated butterfly valve manufacturer makes these valves with or without flange holes on the body. Gaskets and O-rings are placed on a flat face of the valve on the inlet and outlet sides between the pipe flanges to enhance a tight seal free from fluid leakage. These valves are among the most economical and inexpensive butterfly valves. However, this type of gear-operated butterfly valve cannot be used for isolation or end-of-line service. As such, the whole pipeline has to be shut down when performing maintenance on either upstream or downstream sections of the valve.

Gear operated wafer butterfly valve.

Gear-operated lug butterfly valve

This is a gear-operated butterfly valve that is also mounted between two pipeline flanges. The valve and pipe are held together firmly by use of bolts. The bolts are inserted through threaded lugs that are made around the valve body. There are two separate sets of bolts used to hold the valve on each side of the valve. These bolts hold the pipe and valve without the use of nuts. This helps to make the valve suitable for isolation or use in an end-of-line service. Gear-operated butterfly valve manufacturers design such valves to make it easy to dismantle one end of the valve without interfering with the other end. As such, these valves take less maintenance time compared to other valves. The challenge associated with this valves is that it carries the pipeline weight on its body. As such, the valve body should be strong otherwise it will fail under such weight loads.

Figure: Gear operated lug butterfly valve.

Gear-operated eccentric butterfly valve

This is one of the most common butterfly valves. This type of valve has various designs which are characterized by where the stem passes relative to the disc centerline. There are three types of this valve which include:

Single eccentric valve. This is the type of gear-operated butterfly valve in which the stem is installed behind the centerline of the disc. Gear-operated butterfly valve manufacturers design this valve aiming to reduce contact between the disc and the seal before the valve gets fully closed. This design helps to enhance the service life of the valve.

Double eccentric valve. This is the type of gear-operated valve in which the stem is designed to behind the disc with an additional offset. This design allows the disc to adjust itself to the center which promotes a tight seal against fluid leakage.
Triple eccentric valve. This valve is suitable for use in critical applications. Gear operated butterfly valve manufacturer design this valve similar to the double type but with an extra offset. The third offset is the contact axis between the seat and the disc. The seat used is metallic and tapered which helps to reduce wear and enhance efficiency. The metallic seat helps to make this valve suitable for high-temperature applications as well as enhance tight shut-off.

Figure: Gear operated eccentric butterfly valve.

Applications of gear-operated butterfly valves

Gear-operated butterfly valves are used in petroleum refinery and transportation applications.
They are used in water supply and wastewater treatment.
They are used in the mining industries to control the flow of sludge.
Gear-operated butterfly valves are used in the manufacturing of different types of chemicals.
They are used in food and beverage processing applications.
They are used in the control of steam in boiler applications.
Gear-operated butterfly valves are used in the paper and pulp industries.
They are used in firefighting applications.

Advantages of gear-operated butterfly valves

Gear-operated butterfly valves need smaller amount of torque to open and close.
They operate very fast as they need a quarter turn of the handwheel to open and close the fluid flow.
These valves are inexpensive compared to other valves like globe valve.
Gear-operated butterfly valves have a simple and compact design which makes them strong.
These valves occupy a small space during installation.
They are free from fluid leakage.
They are versatile because they are applicable in different industrial applications.
Gear-operated butterfly valves have low-pressure drop which helps to enhance pumping efficiency.
These valves can handle large fluid flow as well as media with suspended particles.
They are easy to install, clean, and repair.
They can be used as shut-off and throttling valves.
They are small in size and light in weight.

Disadvantages of gear-operated butterfly valves

The throttling ability of gear operated butterfly valve is limited to a low-pressure difference.
These valves suffer choking and cavitation.
Applications involving high fluid pressure may need a lot of torque to open and close thus causing a lot of fatigue.
These valves have poor sealing ability compared to other valves like ball valve.

Troubleshooting gear-operated butterfly valves

Valve is hard to open/close

Corrosion in the valve. Open the valve and clean off corrosion.
Foreign materials interfering with disc and stem movement. Open the valve and remove any foreign materials.
The gear is dry. Lubricate the gears as recommended by the gear-operated butterfly valve.

Internal fluid leakage

O-rings are damaged or worn out. Replace the O-rings.
The seats are damaged. Replace the seats.
Damaged valve disc. Replace the disc.

External fluid leakage

Loose bolts. Tighten the bolts to the torque required by the gear-operated butterfly valve manufacturer.
Worn out gasket. Replace the gasket.

Summary

Gear-operated butterfly valves are manual valves with a gear system used to multiply torque applied by the valve operator to make operation easier. These valves operate by making a quarter turn on the disc. The ability of the disc to make a quarter turn is enhanced by the torque transmitted from the handwheel through the stem. Once the disc makes an anticlockwise turn, it becomes parallel to the fluid flow which leaves the flow path open allowing fluid flow through the valve. The valve closes when the handwheel is rotated in the clockwise direction for 90^o degrees which then turns to become perpendicular to the fluid flow. This orientation blocks the flow path hence no fluid can cross the valve.

Gear-operated butterfly valve manufacturers produce various types of these valves which include double flanged gear-operated butterfly valves, gear-operated wafer butterfly valves, gear-operated lug butterfly valves, gear operated eccentric butterfly valves among others. These valves are used in various applications such as paper and pulp, food processing, steam power plants, mining, chemicals, petroleum refineries, and water supply among others. These valves have various advantages among them fast operation, simple and compact design, cheaper, and easy to install, repair, and clean.