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Pulse Jet Pointers
Vol. 7, No. 1

Cleaning Nozzles for Cartridge Collectors,
and Other Thoughts on Aids to Better Dust Control

The external top mounted venturi shown in the illustration below as a bad example, does create a reverse suction toward the top of the cartridge, just as they note in the graph. However most cartridge pulse jet manufacturers have not been using any venturi. A pulse, properly created from a blow tube located 14" above the tube sheet, simply raises the pressure in the area below to about 28" water gauge positive (one psig). Therefore, if you graphed our cartridge, the line would be even more straight than with a nozzle, and at the same wall pressure. The wall pressure is simply the same pressure drop as the operation pressure (3-5" W.G.), except it is reversed for the moment.

If an internally mounted venturi is used (sticks down into the cartridge - the top being even with the tube sheet), nothing much changes from no venturi at all, except it negates the possibility of wear at the cartridge top due to the pulse hitting the media directly. We have never really proved this, but the venturi seems to mollify a few people so we use it if specified.

The external top mounted venturi is not used in the horizontal or slant horizontal designs, which seems to be a configuration of choice by some manufacturers in recent years. To the best of our knowledge, on vertical cartridge units, only a few manufacturers mount the venturi flush with the top as shown in the "bad example." Most, if they use the top venturi, leave a space between the bottom of the venturi and the tube sheet.

Our tests, conducted early in the game, showed that no matter how the venturi was put into play, the big opening of the cartridge simply didn't lend itself to any assistance from a venturi. The secret is to release the pulse high enough so it can entrain other air and raise the pressure, thus blowing the dust off.

Venturis are of great assistance to cleaning in a small opening, such as with 4"-6" bags, and if internally mounted in the top of the bag cage. The proper place for the blow tubes on bag pulse jets is 7" above the tube sheet, as the originators proved some 40 years ago.

There are also nozzles for fastening to the blow tubes in bag collectors, to be used instead of venturis. They come with different size orifices up and down the length of the blow tubes, to even out the pulse flows.

But, the truth is, there are so many divergent air currents inside dust collectors, caused by inlet configuration and the configuration of ductwork ahead of the inlet, that the dust is going where it wants, and fooling around with the pulse is just that - fooling around. Great for research projects, but having small profit for the dally work of cleaning the air.

While we are at it, people often ask about the "Sta-Kleen" diffuser for use inside bag cages. In the perfect dust collector with absolutely even air currents, a diffuser in the cage will even out the bag wear and reduce the pressure drop. It might save 10% on bags over the service life. But users most often change a whole set of bags just to get at two or three that are wearing due to some adverse air current, and the "Sta-Kleen" diffuser does nothing to help this situation, just makes changing bags harder, because the cages are heavier with the diffuser in there.

Best Regards,

Bruce Beckert

 


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Since 1921, Industrial Dust Control, Ventilation and Process Equipment


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