|2. Rotating plugs|
|3. Ball valves|
|4. Rotating pipe|
It may be necessary to have a more complex pneumatic conveying line, than a system where product is taken only at point A and transported only at point B. When there are multiple destinations and / or pick-up points, the installation of pneumatic conveying diverter valves is necessary.
Different types of diverter valves exist (see below) but all must have some characteristics : be tight, and without presenting any obstacle to the flow of particles (pressure drop reduction, hygiene, breakage of particles, blockages of pipe...). A butterfly valve should therefore be avoided for this kind of operation.
Such valves are equipped with an insert with a hollow part (the pipe). The rotation of this plug within a drum allows to divert the flow to one direction or another.
Drum diverter valves are hygienic since, well operated, they avoid any retention of product, and can be tight up to a pressure of 6 bar g. On the other hand, they are quote expensive equipment.
Contrary to the rotating plug valves, a system using ball valves to change direction will require the installation of 2 valves, one for each pipe being supplied
Ball valves can cause the retention of product in between the ball the housing, a special gasket is required in hygienic application to reduce this potential accumulation of product (especially with powders). However, the main drawback of using ball valve is that there will be some retention of product prior to the valve being closed during the transport. It indeed cannot be avoided, sometimes minimized if 1 branch is known to work more often than another. If product cross contamination is a concern, this method is not recommended.
Ball valve can be used for pressure and dense phase.
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Rotating pipes can be used for having a cheap and compact solution when the distribution is needed to more than 2 destinations. Up to a dozen of outlet can be provided.
Such system is often not as tight as the other designs, thus it is reserved for dilute phase conveying. The design is as well less robust, particularly compared to the rotating plug valves.
A flap closing one side of a pipe Y connection is the simpler of the design. It should however be considered only in gravitary transfer since it is particularly un-tight. If applied in a pneumatic conveying line, chances are high that part of the product will end up in the wrong direction. Product can stick to the pipe and prevent it to close properly.