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Conveying
system. Air powered’ Venturi’ systems are ideal for low capacity
conveying, they offer low capital cost and are not as expensive
to run as many potential customers have been led to believe.
Vacuum systems are usually the only choice where customers
want to suck material out of sacks or other open top containers
such as kegs and drums. They are ideal for applications with
multiple inlets too.
Reverse jet, self-cleaning, filters that clean the conveying air,
that has to be returned to the atmosphere after use, reduce
maintenance and minimise product loss.
Pneumatic Conveyors
They are probably the most versatile of all conveying systems
given that other than for cost considerations there is virtually no
limitation on capacity, product type, distance or routing. Lean
phase systems (where the ratio of product to air is low) can
move mountains of product. Dense phase or plug flow systems
move ‘slugs’ of product at lower speeds with minimal
degradation.
Positive pressure pneumatic conveying is generally used to
convey materials from a single source to one or multiple
destinations. Pneumatic conveying systems are normally the
Vacuum Conveying System
preserve of ‘big league’ applications such as the rapid
discharging of road and rail tankers in to silos and the transfer of
not expelled at the outlet. The material is separated from the air product from silos to large-scale production processes.
that carries it and the unloaded air current is directed down the Capacities of up to 100 tonnes / hr are not unusual.
return section of the tube. It is thus retained in the tube circuit. The big disadvantage is the initial cost and also the amount of
An AMC should always be started empty and fed at a filtration required. Again self-cleaning reverse jet filters are a big
controlled rate. With free flowing products, a simple baffle may help in reducing maintenance. These systems must be
be all that is required. In other cases, a controlled feed device maintained free of leaks to ensure efficiency and, above all, to
such as a rotary valve or flexible screw conveyor should be used. avoid the health and environmental issues that leaks cause!
Maintenance needs can be moderate to high. The rope
tension must be adjusted regularly during the all important Other types of conveyors
running-in period and then the tension must be checked Rigid Screw Conveyors – beware the seals and bearings!
periodically thereafter. Rope life depends upon conveyor length, Bucket Elevators – ideal for the most delicate of products but
the number of starts and stops, solids loading and whether generally not for those that are dusty.
routine inspection and tensioning are properly performed. Even Flat Belt Conveyors – mainly used in quarries and mines.
so, rope and disk assemblies on arduous duties have been Vibratory Feeders – Ideal for very short distances.
known to last 8 years and more. Air Slides – okay for dense materials and for downhill
The effort, worry and cost of this regular maintenance can all conveying only.
be avoided by choosing an AMC with an integral automatic rope There are occasions where a mix of conveyor types is
tension monitoring and adjustment system such as the patented appropriate. For example, short easy to clean flexible screw
system offered by Spiroflow Ltd. This one addition to the AMC conveyors are often used as the means to provide a lengthy aero-
can, for some, literally turn a nightmare into a dream! mechanical conveyor with the consistent in-feed of material.
Vacuum Conveyors Conclusion
Vacuum Conveyors are the obvious choice where products have As usual, the well-worn expression ‘horses for courses’ could
to be conveyed over longer distances and torturous routes. not be more true. The key is to find a conveyor supplier who can
Vacuum conveying is usually restricted to throughputs of around prove that he can meet your requirements and who will give you
10 tonnes/hr over 100m. a performance guarantee – after that it’s down to the usual
A vacuum conveyor uses air to convey materials through an commercial considerations of price and delivery. Having said
enclosed pipeline. It provides a solution for users requiring a that, the installation of a conveyor is usually part of a larger
system that is easy to route, has few moving parts, is dust tight project that offers commercial savings, heath & safety and
in operation and empties of product leaving minimum residue. environmental benefits that far outweigh the costs involved –
Vacuum conveyors are the preferred choice for toxic or therefore confidence in the supplier to meet your requirements
otherwise hazardous materials because air is sucked-in in the is probably the most important consideration of all!
event of accidental damage to the conveying tubes thus Author: Steve Taylor, Senior Mechanical Engineer at Spiroflow
minimising the escape of product to atmosphere. Spiroflow are specialists in conveying dry bulk solids and big bag
The motive force is provided by either an exhauster or a side handling. You can contact Spiroflow on tel: +44 (0)1200 422525
channel, high efficiency fan sited at the receiving end of the or visit: www.spiroflow.com
32 Solids & Bulk Handling • August 2007 www.solidsandbulk.co.uk
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