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connections / coupling
|3. Piping bends|
|4. Piping length|
|5. Pressure and vacuum service
Conveying pipes are used in pneumatic conveying to send the product from a point A to a point B. There design is resulting from the considerations of different inputs or constraints.
Among the constraints are the aspects related to the performance of the conveying system and its influence on products. This will fix the pneumatic conveying pipe diameter but also the design of the bends of the pipe layout.
Some inputs will have also to be done by the plant operator, especially regarding the type of pipe coupling (clamping) to be used or the length of pipe sections. The material of the conveying tubing must also be chosen, it can be a standard carbon steel for non sensitive industries (polymer...) or stainless steel (food industries).
Different types of pneumatic conveying pipe couplings are available in the market. The main ones are the following : SMS connections, Morris clamps and flanges. The decision to go for one or the other will depend on the service conditions of the pneumatic conveying line, the habits of the plant operator but also the confidence on the reliability of the conveying line - if the product to be transported is very difficult and blockages are expected, it is better to have quick dismantling connections.
Table 1 : Different types of piping connections and their advantages and drawbacks
|Type of coupling||Picture||Pros||Cons|
Easy to dismantle and clean the pipe
|More expensive - need to have threaded pipes
Sometimes difficult to have a tight connection
|Morris coupling||Less sensitive to pipe alignement vs SMS
No need to have threaded pipe
|Long to dismantle
Not always easy to adjust
|Flange||Tighter connection, can be qualified for high pressures
Long lasting - usually preferred when the pipes goes over long distance outside building
|Very Long to dismantle
Not always easy to adjust
Need to change the gasket at each opening
The design of Conveying Pipe Bends is of particular importance for lean phase conveying where the product is circulated at high velocity. When hitting the pneumatic conveying elbows some products will be damages - fragiles powder breaking and forming fines,
In order to avoid such phenomena, the pneumatic transport bend radius must not be too sharp. As a general rule, the ratio Bend Radius / Pipe diameter should not be below 10.
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Deciding on the pipe section length will mainly depends on the service which is expected for the pipe. If it is expected to be dismantled often for cleaning for example, then short pipe sections are recommended. On the contrary, if the system is not expected to be dismantled, while conveying a single and well known product for instance, then it will be economically sounder to have longer sections.
As a rule of thumbs :
- High frequency for dismantling : pipe section length < 6 m
- No dismantling expected : pipe section > 10 m
When having to dismantle pipes frequently, specific access may be foreseen in order to ensure a safe access to the piping.
The pressure at which will be operated the pipe must be taken into consideration for the choice of the piping but also the coupling required. Although pressure in conveying line is usually moderate, it is a good engineering practice to define the maximum pressure that could happen, especially in case of problem on the line, and chose piping and coupling qualified for a higher pressure.
A proper installation of the coupling is also critical for both pressure and vacuum service. It is important to avoid leakages of product in the case of pressure conveying, which would lead to losses but also to dust explosion risks. For vacuum conveying ingress of air in the pipe must be avoided as it could bring pollutants if the air is not treated or which could reduce the performance of the conveying line by bypassing the inlet of product and reducing the conveying air available at the beginning of the line potentially leading to blockages of the pipe.
It is also possible to use pneumatic conveying hoses in certain circumstances to conveying pneumatically materials. It is for example the case when discharge a truck tanker by pneumatic conveying : the truck is connected to the conveying pipe thanks to a flexible pneumatic transfer hose, whose material must be strong enough to resist to the wear induced by the material flow.