As the two most common forms of pipe elbow, you’ll find short or long radius elbows in almost any pneumatic conveying system you encounter. But despite over a century of use in materials conveying, many engineers still select elbows without considering their effect on the system and its products.
Choosing suitable elbows for your pneumatic conveying system lets you minimize a number of common operational challenges, such as:
- System pressure drop
- System wear
- Product degradation
- System downtime
- Corrosion
- Erosion
- Shredding
- Streamers
- Contamination
Failing to address these issues can be hugely detrimental to the efficiency, production capacity, and longevity of your conveying system. Not only does this limit your profits, but it also inflates repair and replacement costs.
To install elbows that maximize your system’s performance while limiting maintenance overheads, it’s important to understand the differences between short and long radius elbows.
Short radius elbows
Size
Typically, a short radius elbow has a centerline radius of 2.5 to 4 times that of its outer diameter. The radius of curvature on a short radius elbow also matches the nominal diameter of the pipe. This sharp turn means the total volume of a short radius elbow is kept to a minimum, making it suitable for pneumatic conveying systems housed in tight areas.
Advantages
Since a short radius elbow requires less material to produce, it’s both less expensive and lighter than a long radius elbow. It’s also easy to install, and by extension easy to replace once it wears out. This means you endure less system downtime when components reach the end of their lifespan.
Disadvantages
With its sharp angle of impact, a short radius elbow typically receives the force of conveyed materials in a single spot. While this isn’t much of a problem when processing soft products, more abrasive materials increase the chance of an elbow blowout. More money must then be spent to replace the components, leading to avoidable expenses when the elbow is installed in an improper location. The force of impact also leads to higher product degradation, lowering the quality of products your clients receive and further risking lost income.
Long radius elbows
Size
A long radius elbow has a significantly longer centerline radius than its short counterpart, measuring 10 times or greater than its outer diameter. While using a long radius elbow will cause your pneumatic conveying system to occupy more space, most facilities are able to comfortably accommodate them.
Advantages
The main advantage of a long radius elbow is the wear protection afforded by its shallower angle of impact. Since products drag along the back of the elbow rather than impacting a single point, a long radius elbow benefits from reduced wear and lower product degradation. This means that a long radius elbow typically has a greater lifespan, reducing the time and cost required to keep your pneumatic conveying system at peak productivity.
Disadvantages
While a long radius elbow suffers less damage to a single point, products that bounce can create multiple wear points. These are more difficult to predict and monitor, making it harder to anticipate when your long radius elbow is at risk of blowout. However, this is less likely in dilute phase conveying, as these systems transport lighter particles.
Should you use a short or long radius elbow?
In general, a long radius elbow offers the greatest degree of practicality in pneumatic conveying systems. Despite its higher price point and larger size, its innate resistance to wear protects your pipes and your products against damage. This is why long radius elbows are typically the elbow of choice for operations without special requirements.
But the additional benefits of a long radius elbow don’t apply when transporting materials that smear, create streamers, or have a small particle size. That’s because the increased drag across the back of the elbow actually increases degradation in these products. In these cases, using a short radius elbow will lead to higher quality products for your clients.
When choosing a short or long radius elbow for your pneumatic conveying system, you should consider your available space and the properties of the material you transport. Since you can use both types of elbows within the same system, each change of direction should be considered individually. Bear in mind that factors like the increased speed at the end of a long stretch of pipe should also factor into your decision.
What to do if you continue to experience elbow wear
If the elbows in your pneumatic conveying system are degrading quicker than expected regardless of their size, you might require a more specialized solution. Both short and long radius elbows have specialty wear alternatives that fit in the same place without adjusting your conveying lines. These include tile elbows, replaceable back elbows, impact elbows, channel back elbows, and elbows with special coatings.
For expert guidance in finding specialty wear elbows for your pneumatic conveying system, Progressive Products Inc. is here to lend a hand. Contact us by phone or email, or fill in our convenient contact form to schedule a meeting today.
