General
Most bag filters have a hopper beneath them for dust collected from each successive blast of compressed cleaning air to clean a row of bag filters.
(Filters installed directly on a silo, called “bunker” filters, are excluded from this need.)
The hoppers underneath the filters must be continuously emptied of the collected dust, and should never be used as a dust store.
Dust evacuation devices are studied in this section. GORCO always offers them for the filters it manufactures, but can also offer them separately and independently, in any other bulk material movement application.
The most important are described below.
Rotary valves
These are used for the most typical dust evacuation devices. They consist of a rotor operating at low speed within the casing or stator.
The valves are moved by means of a gear motor.
Direct mounting / with coupling / sprockets and chains, etc
The most important requirement of a rotary valve, apart from its capacity, is its sealing; so that it prevents air from entering the filter from the bottom up.
Air entering through the edges of the blades or through the covers has several negative effects:
- it removes air from the equipment’s own suction requirements
- it makes it difficult for dust to fall, with the associated risk of jamming
- leads to abrasiveness due to friction
GORCO has a wide range of standard sizes, from 11 l/v to 400 l/v, and can calculate the models of sizes and requirements necessary in special applications.
Double flap valves
These are closing and discharge valves made up of two flaps placed one on top of the other, which open and close alternately, guaranteeing a good seal.
They can be operated in different ways, with the following:
- counterweights.
- single gear motor and timing cams.
- double cylinder.
- double cylinder and intermediate recipient.
They are useful with abrasive materials, as wear due to friction is much less than in rotary valves.
Counterweights are cheap but not useful with very light powders.
The double butterfly with intermediate recipient are of interest as final components in negative pressure pneumatic conveyors.
Screw conveyors
Filters with hopper trough type include screw conveyors in the bottom.
They consist of a helix welded to a shaft, which pushes the material deposited on it when rotated.
They can be of the closed type: tube or trough
Or open, typical arrangement at the bottom of elongated trough hoppers under filters.
The calculation of parameters such as diameters, shaft section, speed and installed power is critical for their operation. GORCO has designed and manufactured hundreds of screw conveyors, from small (80 mm) to large (600mm) diameters, in heavy duty applications.
The screws must always be supplied with the drive gear motor, coupling, rotation controller and all necessary control components.
Airslide type
These are not mechanical devices.
They are designed as box-type components with a slight inclination (of 5-10°), divided into two zones by a porous fabric. The solid “slides” over the top, aided by the fluidising air supplied under the canvas from a motor fan.
They are simple, cheap devices for materials that can flow. The temperature is limited by the fabric properties, which are generally simple fibres such as polyester.
