A Guide to Selecting Pneumatic Conveying Bends
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The types of bends you install in your pneumatic conveying system have a direct impact on your system lifespan and product quality. By choosing first-rate, well-fitting parts of the right sizes and materials, you can avoid common problems such as shredding, streamers, contamination, product degradation, blockages, corrosion, erosion, and unexpected pressure drops.
But while finding compatible pneumatic conveying bends might seem simple, it can be a huge problem for even the most experienced process operators. That’s because research on bends is often inconsistent, and public findings are frequently at odds with field experience. So when you need advice on selecting pneumatic conveying bends for your system, it’s vital that you take it from a trusted expert source.
Manufacturers across the world rely on the knowledge and expertise of PneuComponents to find industry-leading parts that reduce downtime and boost productivity. In this guide, we provide reliable information on the various types of pneumatic conveying bends available and how you can make the right choices for your system.
Types of Pneumatic Conveying Bends
Not all types of pneumatic conveying bends are appropriate for all types of systems. Some applications require hard-wearing components that withstand impacts and abrasion, whereas others rely more on corrosion resistance and sanitation. The materials you choose for your pneumatic conveying bends should depend on the characteristics of your products and your operational goals.
The addition of carbon makes these steel bends one of the most durable and abrasion-resistant options on the market. Carbon steel is around 2.5 times denser than aluminum, making it an incredibly strong material. And since this added strength means carbon steel bends can be thinner, they’re also very cost effective.
However, carbon steel bends are more prone to rust than other types of pneumatic conveying bends. So they shouldn’t be used for conveying liquids nor in applications in which condensation is a concern.
Stainless steel bends contain high levels of chromium, which creates a protective barrier that resists corrosion, rust, and oxidation. This makes them compatible with many chemicals, and the fact that they’re easy to clean and sanitize makes them a common sight in food processing systems. They offer high resistance and tensile strength, and safely function between -270 – 400oC.
But stainless steel bends require more labor to form, weld, and machine. Add in the increased costs of the material, and you’ll find they’re typically more expensive than other options.
Light, affordable, and easy to fit, aluminum bends are a great option for those on a tighter budget. Their high corrosion resistance also provides optimal airflow and higher air quality, which can lead to further reductions in energy costs.
Compared to carbon steel and stainless steel bends, however, aluminum bends aren’t as durable. The soft material makes them a poor choice for use with abrasive products, though they’re popular for conveying non-abrasive plastics and other similar dry bulk solids.
Steel vs Aluminum Bends
The characteristics of steel and aluminum bends make them suitable for different applications. Here are some of the main factors that you should consider when making your choice:
Strength-to-weight ratio: Both carbon steel and stainless steel bends are stronger than aluminum bends. They’re far more abrasion and impact resistant, and don’t deform or bend as easily under weight or heat. However, aluminum bends tend to be around a third as heavy as steel bends.
Cost: Pound for pound, aluminum is more expensive than steel. But because aluminum is significantly lighter, you can get more material per pound. This makes aluminum bends a cheaper option overall.
Abrasion resistance: The softness of aluminum means it’s quick to wear away under abrasion. Steel bends have high abrasion resistance, meaning they don’t need to be replaced as often and can help limit maintenance costs and downtime.
Corrosion resistance: While carbon steel is vulnerable to corrosion, the chromium in stainless steel gives it high corrosion resistance. But the naturally occurring oxide film of aluminum outclasses both. Outside of extremely acidic or base environments, aluminum bends don’t tend to corrode or rust, and don’t need additional coating or painting to operate effectively.
Food safety: Aluminum can react with food products, spoiling their taste and color. Stainless steel, on the other hand, doesn’t typically react with food. For this reason, stainless steel bends are commonly found in food processing facilities.
What is the difference between an elbow and a bend
A “bend” is a generic term for any component that changes the flow direction of materials within a pneumatic conveying system. But while all elbows are bends, not all bends are elbows. The fundamental difference between the two is the radius of curvature.
The radius of curvature of an elbow is generally one or two times the pipe diameter. Bends, on the other hand, often have a radius of curvature of more than twice their pipe diameter. Elbows create sharp corners in pneumatic conveying systems that abruptly change flow direction, whereas the longer centerline radius (CLR) in bends offers a much smoother curve.
Other differences between pneumatic conveying elbows and bends include:
• Elbows follow weld-fitting standards for size, angle, and bend radius. Pipe bends don’t
• Since bends are manufactured from curved tubing, they have a consistent design. Elbows are forged or cast
• Elbows are pre-made, but bends tend to be custom manufactured
How to select the right bend size
Matching the diameter of your pneumatic conveying bends to the measurements of your other pipes and components is common sense. But what many system designers don’t consider is the unique attributes of bend radii.
Short- and long-radius bends will affect your pneumatic conveying system in different ways. It’s important to understand the differences between the two – as well as how to measure these components accurately – to achieve optimal performance.
Short-radius vs long-radius bends
The radius of a pneumatic conveying bend affects how your dry bulk materials are conveyed through your handling system. Depending on the bends you choose, this can either preserve or reduce product quality. Your choice of bends throughout your system should be based on the properties of your materials, as well as your available space.
Remember that your pneumatic conveying system can include both types of bend. So you should consider the best option for each individual change in flow direction. Factors such as increased speed at the end of a long stretch of pipe should also influence your decisions.
Short radius bends
Short-radius bends are around 3-7 times the radius of curvature. Since they’re shorter, they require less material to produce and so tend to be less expensive. These bends are very easy to install and much easier to replace, meaning less system downtime when they wear out. They also allow you to design a more compact system, making them viable in facilities with restricted space.
However, short-radius bends create a sharp angle of impact when changing flow direction. That means they receive the force of conveyed materials in a single spot. While this isn’t an issue for soft materials, using short-radius bends to convey heavy or abrasive materials can lead to an increased risk of blowout. As such, you may find yourself spending more money than necessary on component replacement.
The greater force of impact can also lead to higher product degradation. This lowers the quality of the products your clients receive and reduces the amount of salable product you produce.
Long-radius bends are around 8-14 times the radius of curvature. These tend to be the bend of choice for pneumatic conveying systems as they provide a more gradual change in flow direction. Rather than impacting a single point, materials drag along the back of the pipe, reducing wear and product degradation. This, in turn, can lead to longer component lifespan, reducing costs and overall downtime while increasing productivity.
But while these bends suffer less damage at a single point, products that bounce can create multiple points of wear. As such, it can be more difficult to anticipate and plan for component blowout, possibly increasing unexpected downtime. Thankfully, this isn’t a major concern when transporting lighter particles.
Which is right for your system?
In general, long-radius bends are the most practical choice for the majority of pneumatic conveying systems. Although they tend to be more expensive, their greater resistance to wear protects your pipes and products from harm. This allows you to minimize downtime and maintenance costs while raising the quality of your products.
However, the benefits of long-radius bends don’t necessarily apply when it comes to conveying materials that smear, create streamers, or have small particle size. That’s because the increased drag across the back of the pipe actually increases product degradation in these applications. In such cases, designing your system with short-radius bends in mind can deliver superior results.
(Tubes, Pipes & Glasses)
Offering a variety of short and long radius bends to fit your pneumatic conveying system.
How to measure Centerline Radius
In order to get bends that properly fit your pneumatic conveying system, you need to know your CLR. If you don’t, your components will be more likely to fail, leading to lost productivity and higher maintenance costs.
The CLR is the distance from the exact center of a bend’s curve to the centerline (axis) of the pipe. To calculate CLR, measure from the center point of the bend to where the degrees-of-bend lines intersect. The distance from the intersecting points to the elbow’s center is your CLR.
OPTIMIZE YOUR SYSTEM WITH CUSTOM BENDS THAT SUIT YOUR PRODUCTS
Understanding the values of different bend sizes and materials makes it easier to select components that boost efficiency and reduce downtime while maintaining product quality. But when it comes to ordering those components, most suppliers still subject you to a lengthy ordering process. That costs you significant time that would be better spent elsewhere.
With the PneuComponents online store, you can order carbon steel, stainless steel, and aluminum bends of any degree or centerline radius in just a few clicks. And if we don’t have the parts you need, we can custom manufacture them to suit your specifications.