There are hundreds of different types of elbows available for pneumatic conveying systems. But in general, we can put these into three simpler categories: short-radius elbows, long-radius elbows, and impact elbows. This article will be covering sweeping elbows which have 2D tangents versus weld elbows that do not have tangents. With the exception of the softest and lightest materials, your pneumatic conveying system bears a huge amount of impact and abrasion every day. Over time, the elbows of your system will wear away and need to be replaced.
If you find that your pneumatic conveying elbows need replacing much more frequently than you expected, it might be that you have the wrong types of elbows installed. Using an inappropriate elbow means a higher risk of pressure drop, system wear, and product degradation, as well as lost productivity from increased system downtime.
Which types of elbows are right for your pneumatic conveying system? This depends on a lot of different factors, making it hard to decide. We’re here to guide you to the best choice for your operation and help you improve efficiency. This will in turn save you money and prolong the life of your system.
What are the different types of elbows?
There are hundreds of different types of elbows available for pneumatic conveying systems. But in general, we can put these into three much simpler categories: short-radius elbows, long-radius elbows, and impact elbows.
Short radius elbows
Short-radius elbows have a centerline radius of 2.5-6x the elbow’s outer diameter. These elbows are popular because they’re widely available, very affordable, and very easy to install. But their severe angle of impact means they tend to endure a lot of damage in a single spot, making them more likely to blow out. So, short-radius elbows should preferably be used for the low-abrasion product to avoid the cost and lost productivity of constant replacement.
Long radius elbows
As the name suggests, long-radius elbows have a much larger centerline radius than their short counterparts, with 7x or more than the outer diameter. This means they take up much more space, but their added benefits may be well worth it.
With their shallower angle of impact, product drags along the back of the elbow rather than bounces off it. This reduces impact and spreads wear more evenly, meaning both your elbows and product don’t suffer so much degradation, even when transporting more abrasive materials.
But this doesn’t mean long-radius elbows are always the right choice. When dealing with materials that smear or create streamers, like polyethylene pellets, the increased drag times causes much greater degradation to the product. Similarly, products that are more prone to bouncing will impact a long-radius elbow at many points, causing wear throughout. In this case, a short radius or impact elbow would be more appropriate, as the additional wear would occur in the outlet pipe, not the elbow itself.
This category includes short-fitting style elbows that protect against abrasion through mechanical means. Both dead-end (or “blind”) tee and vortex elbows are great for minimizing abrasion and product degradation, and channel-back (or “hollow-back”) elbows fill up to allow the product to wear against itself.
These qualities make most types of impact elbows a great option for abrasive materials. The same can’t be said for moist, cohesive, or sticky materials, however, as these can create blockages.
Other considerations for pneumatic conveying elbows
If we were to simplify the previous section, we’d say:
- Use short-radius elbows for softer materials.
- Use long radius elbows for more abrasive materials.
- Use impact elbows for highly abrasive materials.
While this is a good place to start, choosing a pneumatic conveying elbow is a bit more complicated than matching how abrasive your product is. Once you have an idea of the types of elbows that you might want to use, you can narrow down your specific choice based on your:
- Tonnage per hour: The more material you convey, the faster wear will occur. If you have a high tonnage per hour, you’ll save money in the long run by paying for a stronger, more abrasion-resistant elbow that can take more punishment.
- Variety of material: It’s much easier to choose the right pneumatic conveying elbows when you only transport a single type of material. Conveying more than one material or a blend of materials means you need to choose an elbow that’s suitable for all.
- Particle size: The size of particles directly affects their force of impact. If you transport large particles, expect greater wear on your elbows.
- Pipe length: Material that’s constantly moving through elbows won’t have time to build up speed. But if you’re replacing an elbow at the end of a long stretch of pipe, the new one will need to withstand much greater force, even from typically low-abrasion materials.
- Operating pressure: The pressure in your pipes affects the tonnage and speed of the product you convey. Knowing the pressure gives you a great deal of insight into material behavior and wear patterns within your pipes, letting you choose an elbow that suits your predicted risks.
- Operating temperature: Your materials are likely to have different properties at different temperatures. So, rather than consider them at room temperature, look into the operating temperature of your system, and how that might affect the behavior and abrasiveness of the product you’re conveying.
Remember that the elbow you choose needs to match the pipe size, tube size, connection, alloy, and centerline radius of your existing pipeage. It’s basic, but it’s easy to forget when you’re too focused on the types of elbows and the materials they encounter.
Always get an expert opinion on pneumatic conveying elbows
Knowing what to look for in a pneumatic conveying elbow makes it much easier to identify your needs, talk through your options, and care for your system. But when it comes to choosing the right types of elbows, it’s always best to ask an expert.
Contact Progressive Products Inc. today to discuss your pneumatic conveying needs, and we’ll match you with the perfect solution in no time flat.