(121c) Comparative Evaluation of Elbows for Pneumatic Conveying Systems

Selecting an elbow for your pneumatic conveying system can be a critical task, especially considering how many different types of elbows are on the market. Yet a properly selected elbow can keep your system operating at peak performance levels, decrease maintenance costs, and minimize material attrition and elbow wear.

Each elbow provides a change in the conveying line direction, and every direction change adds to the system's pressure loss (that is, kinetic energy loss and friction loss and reacceleration pressure drop). The amount of pressure loss depends on various factors such as actual conveying velocity in the elbow, product factors, elbow design and shape. The pressure loss per elbow needs to correctly considered taking into account the different velocity and phase changes as the material passes through the elbow. Another major concern to be addressed is the impact of elbows to product degradation and to wear issues in general.

Selection criteria are typically driven by different objectives, meaning that certain requirements from the product or the system will take priority over others, but in most cases minimum pressure drop with the least amount of product degradation or equipment wear should be the ultimate goal for the right selection of your conveying elbow .

This paper provides descriptions of commonly used elbows, their advantages and disadvantages. By comparison of pressure drop charts, charts on product degradation due to friction when conveying plastic pellets, the selection and decision process may become a little easier by providing a guideline for making the right choice on one very important (but sometimes overlooked) link in your transfer system.