Low pressure and vacuum:Screw feeders and The simple screw feeder.

Screw feeders

Much of what has been said about rotary valves applies equally to screw feeders. They are positive displacement devices, feed rate control can be achieved by varying the speed, they can be used for either positive pressure or vacuum pipeline feeding duties, air leakage is a problem when feeding into positive pressure systems, and they are prone to wear by abrasive materials.

The simple screw feeder

A simple type of screw feeder is shown in Figure 3.15. Rotation of the screw moves a continuous plug of material into the pipeline, where it is dispersed and entrained with

Pipeline feeding devices Part 1- Low pressure and vacuum-0039

the conveying air. A particular advantage of screw type feeders is that there is an approximate linear relationship between screw speed and material feed rate, and so the discharge rate can be controlled to within fairly close limits.

This type of screw feeder, however, is rarely used for feeding positive pressure conveying systems. This is because there is little in their design to satisfy the basic requirement of feeding across an adverse pressure gradient. Air leakage represents a major problem with many materials, and so they are generally limited to vacuum systems where operating pressure differentials do not have to be considered.

The simple screw feeder, however, can be used in high pressure applications in combination with a lock hopper. The simple screw feeder has also been adapted for high pressure duty with the incorporation of a variable pitch screw. Both of these cases are considered in Chapter 4.

Related posts:

Benefits, drawbacks and operational issues:Motordesign
Low pressure and vacuum:Hopper off-loading and Trickle valves
Particle degradation:Recommendations and practical issues
THE COMPRESSOR:ACCEPTANCE TESTS
BASIC PRINCIPLES:GAS LAWS AND THERMODYNAMICS.
BASIC PRINCIPLES:PROPERTIES OF AIR AND GASES
Basic principles:nomenclature and units
Troubleshooting and material flow problems:Non steady feeding of pipeline
Design procedures:The use of test data in system design
Material property influences:Conveying capability correlations.
ACTUATORS:CONVERTING SCFM INTO COMPRESSOR HORSEPOWER
Air Compressors, Air Treatment and Pressure Regulation:air receivers and compressor control
PROPERTIES OF PURE SUBSTANCES:THE IDEAL-GAS EQUATION OF STATE
THE SECOND LA W OF THERMODYNAMICS:PERPETUAL-MOTION MACHINES
HEAT EXCHANGERS:THE LOG MEAN TEMPERATURE DIFFERENCE METHOD

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