What is a Pneumatic Butterfly Valve and Its Working Principle

Pneumatic Butterfly Valve and Its Working Principle

Pneumatic butterfly valves are general-purpose valves with a lot of applications.

Various sectors make use of pneumatic butterfly valves – from the paper industry to the chemical and medical sectors.

In this article, we’re going to explore what a butterfly valve is and its working principle.

We’re also going to cover everything there is to know about this valve including its parts, types, applications, and more.

Let’s dive right in.

Video – Working Principle of Pneumatic Actuator and actuated butterfly valve

What is a Butterfly Valve?

A butterfly valve is a type of valve that relies on quarter-turn rotational motions.

It is typically used in a pipeline system to turn off or modulate flow.

It is a lightweight device with a minimal installation footprint, low costs, and easy operation.

This type of valve is available with huge orifice sizes as well.

The butterfly in its name comes from a disk attached to the rod.

Upon opening the valve, this disk rotates and allows fluid to permeate or pass through.

To close it, a quarter turn is required to rotate the disk to a position that is perpendicular to the direction of the flow.

Below are the advantages of using a butterfly valve over alternatives:

  • Compact and Lightweight

The small face-to-face dimensions and compact design of the butterfly valve result in a minimal installation footprint and greater savings due to low installation costs.

  • Low Maintenance

The simple and economic design of the butterfly valve means fewer moving parts that are worn down and require less maintenance.

  • Fast Acting

The butterfly valve can be completely closed or opened. Larger valves, however, require a gearbox to reduce operating torque and simplify the operation while sacrificing speed.

  • Versatility

There are a lot of possible use cases for butterfly valves. The list includes its suitability for underground installation.

  • Low Costs

Butterfly valves generally need less material, making them an economical choice. This is even more evident when you opt for large valve sizes.

Butterfly Valve Parts

Here are the major components of a butterfly valve:

  • Valve Body

This is the part that you will find between the flanges. The end connection type is typically any of the following: double lug, wafer, or flanged.

  • Disk

There is a disk connected to the valve body. It serves as a gate and throttles or stops the flow of fluid. This component is often bored so that it can receive the shaft or stem. Disk designs vary wildly based on material and orientation to suit the desired flow, operating torque, and sealing.

  • Stem

The valve stem or shaft allows for the connection of the disk and actuation mechanism. It is what allows for the transmission of the torque.

  • Seat

This refers to the anti-leak seal or elastomer that helps keep the disk in a closed position for total shutoff. Ideally, the seat face should be resistant to both erosion and corrosion.

  • Seals

You will find seals at numerous interfaces inside the valve. They deliver a tight seal and isolate the process media from the internal components of the valve to ensure cost-efficiency and flexibility.

Butterfly Valve Working Principle and Function

In general, the butterfly valve construction is quite simple.

The underlying principle here is that rotating the valve disk controls the flow of fluid.

The disk falls into alignment with the piping, while the stem attaches to a handle on the exterior of the valve.

While closed, the disk bars the valve bore.

When it is in the open position, it is positioned perpendicular to the direction of the flow to facilitate flow.

A seal in the stem packing prevents any leakage along its stem.

When the handle rotates the stem 90 degrees, the disk follows the motion and becomes parallel to the fluid flow itself.

Partial rotation allows for the throttling or proportionality of the flow.

A butterfly valve provides shutoff capability and bi-directional flow.

Keep in mind that it is not full-bore, so it is not suitable for swabbing or pigging.

The material of the body is typically ductile iron coated with epoxy powder on the interior and exterior surfaces.

Butterfly valves are often operated by gears, actuators, handwheels, or some combination of these pieces of equipment.

It depends on the technical specifications and specific requirements of the application.

Below are the numerous ways to actuate or operate a butterfly valve, ranging from manual to semi-manual to fully automatic:

  • Manual

This relies on a crank, lever, or handwheel for the operation of the valve. It is common to find a lever in smaller manual valves. This type is inexpensive but easy to use at the same time. For bigger sizes, handwheels are to be expected, frequently accompanied by a gearbox to ensure the transfer of torque with high mechanical advantage.

  • Actuated

When you need to control a butterfly valve or several remotely, power-operated actuators will do the trick. They are designed to stay open or close when there is actuator failure and are frequently accompanied by manual actuation in these cases.

  • Hydraulic

This is typically used in applications that require huge torques. It involves the use of hydraulic pressure to operate the piston for the opening or closure of the valve. You will find this in high-viscosity and high-pressure applications.

  • Pneumatic

This type is commonly used in applications that require high precision. It depends on the use of compressed air to operate the diaphragm or piston for the opening or closure of the valve.

  • Electric

Meanwhile, this type calls for an electric motor for rotation when it comes to the control of the valve. It is commonly used when it comes to time-sensitive applications and high-precision regulation.

Characteristics of Pneumatic Butterfly Valve

If you want to learn more about the pneumatic butterfly valve, here are its characteristics:

  • Easy to install and disassemble

It is convenient to install and remove pneumatic butterfly valves. This comes in handy for inspection and repair.

  • Resistance to high and low temperature

This type also features good resistance to both high and low temperatures. Its sealing is also excellent, which grants it extended service life and eliminates the need to replace it frequently.

  • Simple operation

It is easy to facilitate the opening and closure of the valve as long as it is rotated vertically at ninety degrees.

Types of Butterfly Valves

Here are the different kinds of butterfly valves, depending on where the stem is located about the centerline of the disk and the valve seat surface angle:

  1. Concentric

This is regarded as the most basic butterfly valve design.

Also called centric, this involves the stem passing through the centerline of the disk and the seat as the inside diameter periphery of the body.

The zero-offset valve design is resilient due to the efficient sealing that depends on the flexibility of its rubber seat.

During closure requiring a rotation of 90 degrees, the disk touches the seat at approximately 85 degrees. This type is ideal if you are using low-pressure ranges.

  • Eccentric

On the other hand, the steam of an eccentric butterfly valve does not have to pass through the disk centerline but behind it.

The stem of a single offset butterfly valve is positioned right behind the centerline of the disk.

This allows for a reduction in the contact between the disk and the seal before the full closure of the valve.

The design ultimately allows for longer service life due to the minimal contact.

It often has higher pressure ratings than the concentric alternative.

There are also different types of butterfly valves based on the connection types used:

  1. Lug-style

In this kind of butterfly valve, there are lugs or threaded inserts outside of the body.

A pair of bolt sets without nuts link the pipe flanges to the sides of the inserts.

The design facilitates the disconnection of a side without impacting the dead-end service function of the other.

In general, those employed in dead-end service come with a low-pressure rating.

What makes it different from its wafer-style counterpart is that it carries the piping weight through the body.

  • Wafer-style

This is largely considered to be the more cost-effective of the two.

The wafer-style valve is sandwiched between a pair of pipe flanges.

Long bolts crossing the whole valve body link the pipe flanges.

The connection type is good if you need to prevent backflow in universal flow systems and seal against bi-directional differential pressures.

There are iterations of this style with flange holes on the valve body exterior.

Flat valve faces, gaskets, and o-rings on the two sides of the valve work together to deliver tight sealing.

Butterfly Valves Applications

Butterfly valves are used in a wide range of applications across different fields, sectors, and industries.

However, their main applications are found in the following industries:

  • Ship Building

Butterfly valves offer durability and reliability, which are important in shipbuilding.

Typically, they are utilized in power generation by making a water-tight shut-off mechanism in the piping to prevent pipe fluid flow.

The small size of the valves makes them perfect for fitting into the tight spaces of the ship.

  • Oil Refinery

Offshore gas pipelines and oil rigs involve harsh environments that call for heavy-duty valves capable of withstanding the aggressive media and hostile environments.

Butterfly valves offer a lot of reliability in this field by ensuring long life and minimal maintenance.

High-performance steel-body butterfly valves and the fire-safe Triple Offset design are ideal for this application. The seated version is suitable if there will be water involved.

  • Food Processing

Food processing calls for strict rules on cleanliness, safety, and quality.

In the regulation of fluid flow in piping systems, there is a need for high durability, low maintenance, and simple design.

The butterfly valve design meets all of these requirements.

  • Pharmaceutical

Butterfly valves are important in pharmaceutical settings since they allow for the transfer of solid products in bulk in accordance with strict health regulations.

However, It is important to ensure regular maintenance and choose materials that will address issues with shedding, oxidation, and contamination.

In general, these valves are used in industries that require fire protection, water cooling, slurrying, vacuuming, and compressed air.

When there is water involved, stainless steel is used due to its high durability and corrosion resistance.

Butterfly Valve FAQs

Here are commonly asked questions about butterfly valves:

  • What are butterfly valves for?

In general, they are used for modulated or on-off fluid control.

There are more specific uses across various fields and industries, but they all boil down to this capability.

These valves may be used for either gas or liquid but not bulk solids.

  • What is the difference between a ball valve and a butterfly valve?

A butterfly valve is often cheaper, easier to install, and lower maintenance.

Its disk, however, makes it unsuitable for pigging.

Ball valves are great in small diameter and high-pressure applications with high-pressure differences and result in less pressure drop.

  • How can I prevent issues with the butterfly valve?

When there is a problem with a butterfly valve, it usually has to do with poor installation.

If you want to minimize maintenance work, the commissioning stage is important.

Keep an eye on the elastomer seal since it has a tendency to move toward the valve face and suffers from compression during installation.

Make sure that the disk can still freely turn upon entering the flanges

Conclusion

We hope this guide has taught you more about pneumatic butterfly valves and butterfly valves in general.

It is important to make informed decisions, especially when it comes to choosing the right butterfly valve.

Make sure to only trust reliable manufacturers and suppliers who can guarantee high-quality products.

INOXCN is a leading brand of stainless steel valves.

The products of the company are highly durable and resistant to corrosion.

Get in touch with us today if you are on the market for a butterfly valve, pneumatic or otherwise!

Allow us to take care of your valve needs so that you can focus on running your business.

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