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:

System and process requirements:Introduction to variable speed concept
Pumping system hydraulic characteristics:Pump curves and Pump operating point.
Compressed Air Transmission and Treatment:Inducted contaminants
Moisture and condensation:Energy considerations and Evaporative cooling.
Material related,Angel hairs and Coating of pipelines.
Review of pneumatic conveying systems:Material property influences
CHARACTERISTICS OF COMPRESSED AIR:DALTON'S LAW
HYDRAULIC FLUIDS:PURPOSE OF THE HYDRAULIC FLUID
Fundamental Principles:IndustrIal PrIme movers
Hydraulic Pumps and Pressure Regulation
INTRODUCTION AND OVERVIE:FLUID MECHANICS
PROPERTIES OF PURE SUBSTANCES:SPECIFIC HEATS
THE FIRST LAW OF THERMODYNAMICS:SOME STEADY-FLOW ENGINEERING DEVICES
ENTROPY:MINIMIZING THE COMPRESSOR WORK
FORCED CONVECTION:LAMINAR FLOW IN TUBES

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