The most destructive component of a pneumatic pipeline is the 90° Bend.
In straight pipe sections the air flow can cushion the travelling particles. The air will assist in smooth transfer of solids through the pipe. However, around a 90° bend in a pipe all the travelling solids will hit the outside of the bend at the same spot on the pipe wall. The amount of wear at this point will be tremendous, especially if the pipe is made of a soft material such as sugar, plastic pellets or fine aluminium powder. In many cases the outside of the bend can erode through in a matter of weeks. This type of wear does not wear the pipe material uniformly throughout the bore. Instead it will concentrate at the one point of the pipe wall. Pneumatic Conveying Systems is covered in more detail at www.aptech.uk.com/pneumatic-conveying-systems.
To prevent such wear there are two effective ways to design pipe work around bends. The first method is to use a blind tee, which appears to be a totally unsuitable piece of pipe work. However, as with all pipe work, the tee is used in the normal manner, with one end of the T being sealed by a plug or flange. The incoming particles of material are deflected into the end of the T, where they are packed by preceding particles into a solid cushion. The next particles to enter the T are then stopped by this cushion rather than by the hard steel of the pipe work, thus preventing serious wear. Blind tees are particularly good at self repairing the wear in the bend. The second method of preventing wear at bends is to take a long radius turn, thereby spreading the area of the high wear over a longer arc. It is often found that a long radius turn will give better service than the most expensive wear resistant lining at a fraction of the cost.
It’s been said before that slowing down the air can be more important than having the toughest material. If you have a fast air stream, the particles hit harder. So slowing down the air slightly can increase the life of bends by a large amount, but this has to be balanced against flow rate, particle density and pipe diameter. look at the safety implications of bend design, not just wear. If a bend fractures, then it can release large amounts of dust into the surrounding area.
