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AMCs: what are they good for?

30 May 2017

James Podevyn explains the differences between pneumatic vacuum conveyors and aero mechanical conveyors (AMCs). 

Product in a pneumatic or vacuum conveyor moves in a suspended stream of gas – usually air. When particulate materials are metered into an airstream, at an optimal solids-to-air ratio, the differential air pressure generated via a vacuum pump creates a high enough velocity to move the materials within the conveying tube.

Pneumatic provides a simple solution to moving material across challenging routes. Product is moved hygienically and is a good fit for many applications.

An AMC is a tubular conveyor that employs a cable and disc assembly. The movement of the conveyor is so rapid that it aerates the product. As a general rule, each pocket contains about 80% air and 20% material. It can offer dust-free and clean handling properties. 

What’s the difference?
AMCs are able to convey material at a rate from 11.8 m3/hr to 51.9 m3/hr, depending on the diameter of the tube. This is achieved using a drive motor between two and 7.5Hp through a gearbox. Pneumatic conveyors require a 20-40 Hp blower to reach comparable rates to an AMC.

Pneumatic conveyors also tend to be louder than AMCs – which can operate below 85dBA – and often need to be remotely installed or have mufflers added to reduce noise levels. This can add to the overall cost of the system.

Multiple outlets on vacuum conveyors require a separate receiver, its own pressurised air supply for filter cleaning as well as its own feed control valve and diverter valves. Additional piping is also needed to feed each individual usage point. Each receiving point requires venting of the motive air as well as filters, valves, diverters, and additional piping to direct product to each use point for pressure systems.

Multiple inlets and outlets can more easily be integrated with AMCs although it is recommended that the conveyor operates at half speed to ensure that the material exits the conveyor properly. 

One of the major advantages of an AMC is that it provides a balanced system. Ambient air is drawn into the conveyor along with the material and the material is discharged at the outlet of the conveyor. The displaced air is drawn back into the conveyor creating the balanced system. There are no special venting or filtering requirements because there is no pressurisation at the discharge point.

Pneumatic systems handle venting differently. A receiver is utilised that requires venting off the motive air. Compressed air is also required for backwashing the filters and valves required for proper operation. Pressure systems require venting with filtration for the receiving vessel with exhaust entering into the surrounding area or vented outside the building.

Vacuum systems generally draw motive air from the surrounding area so it is important to determine whether special air conditioning or additional climate control will be required in these areas. 

AMCs are considered to provide a gentle conveying solution. Pocket fill is typically 80% air and 20% material. The airstream carries the product around any corners in the system and mixtures are maintained throughout the conveying process. While pneumatic conveyors use a similar air-to-material ratio, because the entire length of the circuit is under the same pressure or vacuum – because of centrifugal force – the product hits the walls of the tube hard which can lead to degradation of the material and wear on the machine abd blended products are more likely to separate while being conveyed over long distances.

Pneumatic conveyors can be easily cleaned. They can be dry cleaned using salt to scour the conveyor. For wet cleaning, a ‘pig’ is pushed through the piping system using compressed air. 

AMCs will transfer most of the material introduced into the conveyor. Air purging is an option to clear out any residual material. An alternative solution is dry cleaning, where a material such as salt is run through the conveyor. Wash gates and drains are included when an application requires the system to be wet washed. When wet washing the AMC creates an agitation effect which completely washes the inside of the conveyor and the conveyor can run while empty to dry out.

James Podevyn is UK and Ireland sales manager at Spiroflow.

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