CLITHEROE – Pneumatic vacuum conveyors or aero mechanical conveyors (AMCs) – which is best?
Spiroflow has been at the forefront of the bulk material handling industry for more than 45 years, selling both types of conveyors. In this short article, we cover how each type of conveyor works, their similarities and differences, and how to best determine the best solution for a particular process.
Which is which?
Pneumatic (Vacuum) Conveyors
In a pneumatic or vacuum conveyor, the product is conveyed 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 conveying is a simple option to move material across challenging routes. The product is moved hygienically and is a good fit for several applications.
Aero Mechanical Conveyors
An AMC is a tubular conveyor that utilises a cable and disc assembly. The movement of the conveyor is so rapid it aerates the product. As a general rule, each pocket contains about 80% air and 20% material.
It is one of the most efficient methods of conveying materials. Its dust-free and clean handling properties make the conveyor a good fit for many applications across several industries.
What are the differences?
What makes each stand out? One may be a better solution for a particular process than the other. This next section examines the differences between both types.
Is power consumption a priority?
AMCs can convey material at a rate from 11.8 m3/hr to 51.9 m3/hr depending on the diameter of the tube. These conveyors can achieve this by using a drive motor between 2-7.5 Hp through a gearbox. Pneumatic conveyors require a 20-40 Hp blower to reach comparable rates to an AMC.
Is noise a factor?
Pneumatic conveyors are much louder than AMCs, which operate below 85dBA. Pneumatic conveyors must be remotely installed or have mufflers installed, which adds to the cost of the system.
Does your process require multiple inlets or outlets?
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 easily be integrated with AMCs. When multiple outlets are used we recommend that the conveyor operates at half speed. This ensures that the material exits the conveyor properly. A tube valve at each outlet provides a smooth path for the ingredient to pass through.
What about venting?
One of the major advantages of an AMC is that it’s 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. It is important to determine if special air conditioning or additional climate control will be required in these areas. This could greatly increase the cost of heating or air conditioning and should be factored into an operating budget.
AMCs are considered gentle conveyors. 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.
Pneumatic conveyors use a similar air-to-material ratio. 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. This can lead to degradation of the material and wear on the machine. Blends 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 virtually all of the material introduced into the conveyor. Air purging is an option to clear out any residual material. Another option is dry cleaning, running a material like salt inside of the conveyor. Wash gates and drains are included when the application requires the system to be wet washed. When wet washing the AMC creates an agitation effect, like a dishwasher, that completely washes the inside of the conveyor. The conveyor can run while empty to dry out.
So which conveyor is best?
As not all processes are the same, clearly it’s difficult to say which conveyor would best suit a process without an engineer knowing more a specific operation. At Spiroflow, we have a team of engineers in the UK and the US that can help the decision making process. Please contact us to find out more.