Rotary valves are used to control the flow of many different liquids and gases across a range of temperatures and pressures. This group of valves includes cone valves and plug valves, as well the more popular and widely used ball valves and butterfly valves. The latter two are often preferred thanks to their low cost, durability and reliability.
Given their function, it makes sense that they’re also known as control valves, as they restrict or permit the flow of substances through a pipe. The type you choose will depend on the job you’re undertaking and the particular control valve characteristics you’ll be needing.
In this article, we’re going to take an in-depth look at the difference between a ball valve and a butterfly valve, as well as the pros and cons of each, so you’ll know how to choose the right component for your next installation.
Ball valves: a quick refresher
Recently, we gave you an introduction to ball valves, their applications and how they work. If you need a refresher, read Plastic ball valves: an introduction to their uses and benefits.
Essentially, a ball valve is a quarter-turn rotary valve, meaning that you turn it 90 degrees to open or close it completely. It consists of a ball with a hole through it, and depending on the direction it’s turned in, it either stops, permits or slows the flow of fluid or gas through a pipe.
Advantages of using ball valves
Ball valves are easy-to-use components that are available at relatively low cost. They’re excellent at maintaining and regulating high volume, high pressure, and high flow, making them versatile and appropriate for many different types of applications.
Ball valves are also durable and offer many years of reliable service, and they’re simple to repair or replace. For these reasons, as well as the fact that they offer a tight seal and little to no leak-by when they’re fully closed, they’re one of the most widely used types of rotary valves.
A note about ball valve pressure: a ball valve will turn irrespective of the pressure from the supply side. Moreover, if the hole through the valve has the same (or larger) diameter as the supply pipe, there will be virtually no restriction or pressure drop when it’s completely open.
Best applications for ball valves
Ball valves are commonly used in high pressure gas or liquid lines, roughly 15cm or less in diameter, where total cut-off is necessary.
Typical applications include air, gas and liquid applications requiring a bubble-tight seal; steam services; water services and systems, and low-point drains and high-point vents in liquid and gas services.
Compared to butterfly valves, ball valves offer better cut-off characteristics in high-pressure applications. They also continue to turn easily and don’t require a pressure-balancing scheme.
When you shouldn’t use ball valves
Ball valves are not recommended for sustained throttling applications. They may also not function at their best in a slurry, due to the fact that particles can become trapped in the moving parts and cause failure.
It’s a good idea to install ball valves in applications where they’ll be regularly used. Ball valves that are not used often may seize, and operating them at least several times a year will keep the seals loose and prevent this from happening.
All about butterfly valves
In our piece called Plumbing valves: which type to choose for your next plumbing project, we covered some of the more common types of valves, including butterfly valves. Let’s do a quick revision here.
Butterfly valves are metal disks mounted on rotating shafts, and like ball valves, they’re quarter turn rotary valves used for throttling. When the disk is perpendicular to the flow, the valve is closed and flow is restricted. When it’s rotated 90 degrees, it’s open and permits the flow of liquid or gas. The video below illustrates how a butterfly valve works:
Advantages of butterfly valves
Butterfly valves are lightweight and easy to operate, offer compact design, and are available in a wide range of sizes (including very large) to match the needs of your particular application.
Other advantages include low-pressure drop and high-pressure recovery, a high coefficient of flow, good control capabilities, and openness for less plugging.
Best applications for butterfly valves
Butterfly valves are widely used in chemical, agricultural, water and wastewater treatment services, and due to the fact that they’re also available in small sizes, they’re effective in areas where space is limited.
Typical applications including cooling water and air; fire protection; slurry services; high pressure, high temperature water and steam applications, and vacuum services.
When you shouldn’t use butterfly valves
Butterfly valves don’t seal as completely as ball valves, and therefore are not often used in gas applications – ball valves would be far more effective here.
It can be difficult to clean their internal parts, and therefore they’re not recommended for applications that call for sterile, spotless equipment (for example, medical and food processing applications). Certain types of butterfly valves are not effective in dispensing slurries.
Butterfly valves also tend to cost more than ball valves, due to the fact that certain types require additional controls for their functioning. If you choose high performance butterfly valves for example, the cost will be significantly greater. So, consider a different type if cost is a consideration.
Where to get high quality valves in South Africa
With the basics covered, you should have enough information to make the right choice when choosing your valves. Whichever you select, make sure you opt for high-quality, reliable products that will maintain the integrity of your project.
Plastinternational’s SABS-approved EzeeFlow plastic ball valves offer a superb alternative to brass ball valves (which are heavy to use and may be susceptible to rust). They’ll continue to function like new for many years after installation, and they’re great for your bottom line too.
Learn more about our EzeeFlow ball valves or contact us for advice or a custom quote.