January 14, 2016

5 Min Read
Sweeper Nozzles vs. Fluidizing Disks: What’s the Difference?
Sweeper nozzle and fluidizing pad

The differences between two common pneumatic flow aids, the rubber fluidizing disk and the sweeper nozzle, may not always be obvious. Although they have some similarities, they also contain some very significant design and performance differences that must be considered in order to assure satisfactory and predictable flow in a bulk material handling application.
    
Rubber fluidizing disks are typically meant to be used in applications handling light powders and dry, fine, granulated materials that will aerate easily or flow with gentle vibration. The disks operate by passing compressed or blower air through them, causing the rubber cup to flap and produce vibration energy, while also dispersing air into the stored material to induce flow via fluidization.
    
Sweeper nozzles can be used in both dry powders and also heavier, sticky materials that may not tend to aerate or fluidize at all. The nozzle is basically a one-way valve with a normally-closed, spring-loaded piston head. The piston head forms a dust-tight seal when closed. Compressed air or inert gas is delivered to the nozzle via a high-flow solenoid valve in very short (0.25-0.5 second) pulses, which briefly force the piston head open to allow the pulse to disperse into the vessel. The pulse radiates from the nozzle along the vessel’s inner wall and through the material in a 360 degree pattern, inducing flow by physically dislodging and breaking material buildup and friction along the wall. The compressed air/gas can also serve to aerate and fluidize material, further enhancing flow. The piston head immediately re-seals after each pulse to keep the nozzle dust-free.
    
Fluidizing disks generally install from the inside of the bin, positioned with the rubber cup inverted against the inside bin wall. A hole is cut or drilled in the wall to allow the threaded air inlet to be passed through and connected to piping or tubing on the outside of the vessel, while a lock nut threaded on the outside of the air inlet holds the fluidizer in place on the outside of the vessel wall. The sweeper nozzle is installed from the outside of the vessel by cutting a small hole and welding a threaded mounting coupling in place. The nozzle is then threaded into the coupling and positioned inside the vessel at a depth that allows the air flow to sweep closely along the inside walls. A lock nut holds the nozzle in place once it is properly aligned.
    
Sweeper nozzles often operate at a higher pressure and use a greater amount of instantaneous volume than fluidizing disks, which results in a markedly different influence on material activation, especially when the material is relatively heavy, damp, or sticky. Small fluidizing disks generally specify a 1/4- or 3/8-in. compressed air line or tubing for supply, while the smallest sweeper valve requires a 3/4-in. line supply. Even when operated at the same pressure, it is the difference in volume passing through the supply lines and devices that impacts the amount of force dispersed in the vessel to induce material flow. An apt analogy would be to compare amount of force generated by a garden hose versus that of a fire hose running at the same pressure. In both cases, more volume equals more power.
    
To further illustrate this difference, the following test was performed:

One pound of steel hex nuts, each weighing slightly less than 1/4 oz, were centered in a pile around both a fluidizing disk and a sweeper nozzle, each mounted on a smooth, flat surface. The fluidizing disk was supplied by a 3/8-in. air line, reduced down to 1/4 inch to connect to the fluidizer’s inlet. The sweeper nozzle was connected to a 3/4 compressed air line. Operating pressure for both units was 60 psi.
The sweeper nozzle was pulsed twice in the space of four seconds, with each pulse lasting 1/4 second. The fluidizing disk was activated continuously for 45 seconds.
    
At the end of the 45-second test, the fluidizing disk had pushed the material to a radius extending around it of approximately 4-10 inches. In contrast, in 1/4-second, the sweeper nozzle instantly displaced the material surrounding it to a radius extending approximately 12 to 20 in.

Summary
Both the sweeper nozzles and fluidizing disks are used extensively throughout the world for inducing flow of powdered and granular materials. Each can be an effective tool for flow promotion, when applied in the appropriate manner and for the appropriate material. If your material is light and dry, and will flow readily with a combination of vibration and aeration, the fluidizing disks may be a good choice for a flow aid. However, if the material in your application is relatively heavy, damp, sticky, or otherwise not free-flowing, or you are working with a vessel that may contain a wide range of materials with different flow characteristics, a sweeper nozzle may be the better choice to achieve dependable, on-demand flow.

Watch a video of the comparison test

    Paul Rose has been recommending flow aid solutions to companies throughout the world since 1996. He currently is sales manager for the Airsweep Systems division of Control Concepts Inc., Putnam, CT. For more information, contact Rose at 800-662-4762 or [email protected].

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