Vacuum conveyors are designed by specialists. Here are ten reasons why.
Material weight per unit volume is the main parameter determining how many cubic feet per minute of air (CFM) will be required to convey it. Densities between 25-55 lb/cu ft are usually easy for a vacuum conveyor and it is often light materials that present most challenges: they can require additional filters to suppress dust and separation and therefore need extra power and larger receivers.
Vacuum is often more economical than positive pressure over shorter distances (under 300’ in dilute phase). Sharp turns are equivalent to an additional 20’.
Vacuum conveyors give good control over delivery rate, dovetailing into other processes. As a guide, dilute phase vacuum systems readily transfer 25,000 lb/hr. Positive pressure can move more. Whether throughput is needed continuously or in batches can make a big difference.
Physical characteristics of some materials affect their flow rate due to friction, stickiness or static. Bespoke discharge cones and surface finishes inside the conveyor often address these problems without requiring extra power.
Vacuum is the better method for toxic or inflammable materials, and dense phase conveying for those that are prone to separation or damage.
Inputs are often the most customised part of the system. There are many options depending on how materials arrive on site and are unloaded (see http://www.aptech.uk.com/pneumatic-conveying/vacuum-conveying/ for examples).
Similarly, the operations you are delivering into are a consideration. For example, loss-in-weight feeders need quick refills, augur fillers can use hoppers to ensure there is always an optimum weight of material ready, and line purging valves may be needed if systems are often stopped and started.
Conveyors need some space for equipment at loading or receiving stations. Facility limitations can demand equipment modification or vice versa. Positive pressure conveyors have less space requirement at the receiving end.
Risks to the environment from the material, or to equipment from the environment, can be decisive considerations. Even altitude can affect pneumatic performance.
Pneumatic conveying is excellent for protecting delicate, valuable or sensitive materials because they are enclosed. A range of legal standards apply to all machinery that contacts foodstuffs.
Lastly, calculations are made to ensure receiver, blower, loader, and filters are all matched to work together.