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Pulse Jets--How Do They Work?

A momentary inrush of high pressure air (80-100 psig) flows from the header (12) to the blow pipe, down through each venturi, and into each bag. Thus all the bags in a single row are cleaned simultaneously.

The collector housing is divided by the tube sheet (20). The dirty air plenum (13) is below, with the bags, an inlet (11), and hopper. For some applications the collector mounts directly to a bin or silo, eliminating the hopper and inlet. The discharge of the hopper can be fitted with an airlock (7) to enable continuous discharge of material during dust collecting operations. It can also be fitted with a slide gate or inflatable seal with reusable or disposable drum. The clean air plenum (14) is above the tube sheet and houses the blow pipes, supports the valving, and provides an exhaust outlet (15) for the filtered air stream. A draft gauge (8) shows the pressure drop across the bags.

Beckert & Hiester dust collectors are usually shipped completely assembled. Bags, cages, compressed air header with solenoids and timer are all installed and interwired. If the hopper is not an integral part of the dirty air plenum, it will be gasketed and bolted in place. Legs, if included on the order, will also be attached unless otherwise specified.

Utilities should be connected to the dust collector in accordance with existing codes. Compressed air piping should be sized for the SCFM specified on the job drawing. Compressed air pressure should be 80 to 100 PSI, unless a lower pressure has been specified. In this event, diaphragm valves, blow pipes, and orifices will be larger than usual to accommodate the lower air pressure.

The 115 volt, single phase, 60 hertz timer (1) is either installed in the enclosure with the solenoid valves or in a separate NEMA 4 or 7/9 enclosure as required. It can be installed in a master control panel if desired.

The compressed air supply should be free of contaminates such as water, oil and scale. A water trap, filter, and/or regulator may be furnished with the unit if specified. There are adequate openings on the compressed air header to accommodate a manual drain valve, a quick coupler for air tools to assist in bag changing, and either end connection of the main compressed air supply. All openings not used are plugged at the factory unless otherwise specified.

Bag Type Pulse Jet

 

The filter bags (2) are usually 16 oz. Felt (polyester, acrylic, polypropylene, aramid, TFE, felted glass, or others) and are supported by wire cages (3). The bags and cages are clamped to collars (4) riveted to the tube sheet or a part of the venturi which extends through the tube sheet. "Blow Pipes" (10) with drilled orifices are located above each row of filter bags such that the orifices are directly above the throat of each venturi (9).

Dust laden air enters the collector under pressure or suction from a fan or other air moving device. Pulse jet cleaning takes place when the timer (1) actuates a normally closed solenoid pilot valve (6) causing it to open. The diaphragm valve (5) opens as a result of the decrease in pressure from the opening of the solenoid. 

 

 

1. Timer
2. Bags (or cartridges)
3. Cages (not required w/cartridges)
4. Clamps (not required w/cartridges)
5. Diaphragm Valve
6. Solenoid Pilot Valve
7. Rotary Airlock
8. Pressure Differential Gauge
9. Venturi
10. Blow Pipe
11. Inlet with Baffle
12. Header
13. Housing
14. Clean Air Plenum
15. Clean Air Outlet
16. Slide Gate
17. Seal
18. Drum
19. Drum Dolly
20. Tube Sheet

Cartridge Type Pulse Jet

Generically speaking, the cartridge filter dust collector is a special type of "bag house." The distinction resides primarily in the differences in construction between bags and cartridges.

By pleating non-woven cellulose media and forming it into a canister configuration it becomes possible to greatly increase the media surface area per filter element. This allows for a considerable reduction in the number of filter elements and generally a 25-40% reduction in overall size of the collector housing.

As in a fabric collector, the dust collection action occurs when dust-laden air is moved through the filter element. The dust agglomerates on the surface and the air continues on through the element. Here the similarity ends. In a cartridge element the actual filtering mechanism (the non-woven cellulose) is much finer than fabric and therefore much more efficient at collecting one micron range particles. On a cartridge the actual high-efficiency cleaning action takes lace in the "cake" that is deposited on the pleats. Once the cake is established, new dust will tend to pile up on the outer layers and agglomerate until it is fluffed off by the cleaning mechanism. A charge of air stored in the manifold is released by an air valve upon a signal from a solid-state timer. A pressure of 90-105 PSIG is the throat of the cartridge. It serves to prevent the charge of air from directly hitting the inside of the cartridge. The charge of air leaves the orifice at a velocity of over 500 feet per second and travels downward where it is focused by the venturi. The air charge hits the bottom of the cartridge and bounces back towards the top. This pressurization "fluffs" the cartridge cake by flowing clean air backwards through the cake.

Once the dust is collected on the filters and "fluffed " off of the cartridges, it has become sufficiently heavy to fall through the airstream into the hopper.

Cartridge changes may be accomplished from above or below the tube sheet which divides the clean and dirty air chambers. The selection of bottom or top removal is dependent on customer preference and the requirements of the job.

 

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                 Since 1921, Industrial Dust Control, Ventilation and Process Equipment

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Beckert & Hiester, Inc.
P.O. Box 1885
Saginaw, MI  48605-1885
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