Lean phase pneumatic conveying systems transfer product as a stream of material suspended within a higher speed conveying gas under lower pressure. This type of transfer system can be utilised for both batch and continuous production and uses a blower unit to force conveying air along a pipe line into which the material is introduced. Material is generally fed from a discharge station or a weigher into the conveying line via a rotary valve which not only delivers material at a constant rate but also separates the upstream equipment from the conveying pressure.