In the field of vacuum conveying technology wespeak of vacuum conveyors being used for ٓsuckingmaterial. What actually happens is that the air isevacuated from the suction pipe and the pressure ofthe atmosphere pushes the material into the suction pipeline. It is the atmospheric pressure that indirect-ly performs the work. The stream of air that is formedupon pressure equalisation pulls the solid particles into the pipeline. All vacuum conveyors work according to the samemain principle, as illustrated below. The material is conveyed from a suction point through a pipeline toa container, where...

PIAB vacuum pump B. Bottom valve A C. Inlet container > TM D. Pipeline (hose or pipe system) > PVA E. Feed station F. Filter G. Air shock tanks BCD E FGHA. H. Control system 1.Vacuum is generated by a compressed air-drivenPIAB vacuum pump G )are filled with compressed air.6.When the material container is full, the vacuumpump is stopped. The bottom valve opens and thematerial in the container is discharged. At thesame time, the compressed air in the filter tank is released and cleans the filter7.When the pump is restarted, the process is re-peated and a new cycle begins. The suction anddischarge...

MATERIAL FLOW The material flow is determined by the diameter ofthe conveying pipeline, the vacuum flow, conveying distance and not least by the characteristics of thematerial. The relationship between material flow and vacuumflow is usually stated as phase densities and is a di-mensionless quantity. If the phase density is thesame as the bulk density, it means that there is noair in the conveying pipeline and that the pipeline is blocked. The converse also applies. If the phasedensity is equal to zero, there is no material in theconveying pipeline. Between these two limits, a range of phase...

It is generally the case that in dense phase, becausethe material moves in the form of plugs, the vacuum level is usually 30ٖ65%, while in dilute phase it is1030%.When sizing a conveying installation, it is importantto find the optimum conveying phase for a specificmaterial. A common misapprehension is that thegreater the vacuum flow, the higher the materialflow. The relation between material flow and vacuum flow may, for example, be as shown in the oppositefigure. The diagram shows that the maximum mate-rial flow Q Q Material FlowQ maxQ vQ Vacuum Flow > TM PVA max is equivalent to the vacuum...

MOISTURE SENSITIVITY Different materials are more or less hygroscopic. Iftest running is carried out on a particular material, itis important that the conditions are kept as similaras possible to those that will apply on installation. A moisture-sensitive material may form lumps thatcatch in the material intake, stick in the pipeline orblock up the filter. > BULK DENSITY The term ٓbulk density refers to the weight/volumeof a material, in other words, how much one litre ofthe material weighs. As one litre of powder containsboth material and air, the bulk density will vary con- siderably depending...

HARMFULNESS AND TOXICITY A vacuum conveying system is appropriate for con-veying harmful materials, as any leakage in the sys-tem does not allow the conveyed material to leak outinto the surroundings because of the lower pressure within the system.The air extracted from the system may need to be fil-tered particularly carefully by means of a special fil-ter or be piped away to a central filter system > EXPLOSION RISK In connection with handling of finely ground material,there may be a risk of dust explosion. Dust explo-sions can occur when certain types of particles aremixed with air at a certain...

GENERAL From a technical point of view, pneumatic conveying is based on conveying of solid particles mixed with a gas, usually air. By means of pneumatic conveying, solid particles ofvarying sizes can be conveyed between points, forexample, from a storage to a processing machine.Pneumatic conveying depends on access to com-pressed air or a source of vacuum, a feed device where air is mixed with the solid particles, a convey-ing pipeline and a receiving device that separatesthe carrier air from the particles. PNEUMATIC CONVEYING SYSTEMS ARE DIVIDED INTO THREE CATEGORIES: Positive-pressure systems,...

POSITIVE-PRESSURE CONVEYING SYSTEMS > TM PVA Positive low-pressure system, pressure about 0.1 MPa The advantage of positive-pressure systems is thatbulk material can be distributed from one source toseveral locations through a system of valves.Usually, positive-pressure systems are divided intolow-pressure and high-pressure systems. A high- pressure system has much greater capacity in re-gard to the quantity of material that can be conveyedand also allows significantly longer conveying dis-tances than are possible with low-pressure systems.In low-pressure systems (pressure 0.1 MPa) bulkmaterial...

VACUUM CONVEYING SYSTEMS With vacuum systems, material can be sucked fromseveral pick-up points and collected at one receivingpoint. This is the opposite of what happens in posi-tive-pressure systems. Vacuum systems have lower material flows than positive-pressure systems. Max-imum conveying distances may, with favourable ma-terials, be 100ٖ150 m.The limitation of the conveying capacity is due to thefact that vacuum systems utilise only atmosphericpressure, while in positive-pressure systems consid-erably higher pressures can be achieved. FLUIDISED BEDS In fluidised beds the air passes through...

ADVANTAGES - DISADVANTAGES OF DIFFERENT PNEUMATIC CONVEYING SYSTEMS > Conveying system Advantages Disadvantages Positive high-pressure system Long distance conveying Risks of leakage High capacities Heavy installations Expensive components Wear on material and system > TM PVA Positive low-pressure system Little wear on material and system Limited conveying distance Continuous flow Risks of leakage Feeder often needed > Vacuum conveying system No leakage of material Limited conveying distance Simple to install Dustless Limited capacity Easy to control Usually intermittent operation > Fluidised...