In our last article, The Truth About Paddle Style Bulk Bag Dischargers, we reviewed the design and functionality limitations of paddle style big bag unloaders.
In this article we will investigate the alternative to paddle style bulk bag unloaders focusing on:
- Ergonomics and safety
- Dusting
- Flow inducement
- Outlet spout clamps
Safe and Efficient Bulk Bag Discharger Design
Before we get into the details, I’ll reveal what I believe to be an excellent alternative to paddle style bulk bag dischargers that is based on well over 20 year of continuous use in many industries and applications around the world: the hopper style bulk bag discharger.
This is a relatively simple design that requires no moving parts (other than a totally enclosed electric vibrator) that has proven to be, in comparison to paddle style dischargers, easy and safe to use, excellent at containing dust and extremely effective at inducing flow.
Further, hopper style big bag unloaders do not require outlet spout clamps to try and solve inherent design problems as do paddle style dischargers (although as you will learn below, hopper style dischargers and outlet spout clamps are two of three design elements that comprise total dust containment bulk bag dischargers!).
How A Hopper Style Bulk Bag Discharger Works
- The bulk bag is lowered completely into the hopper.
- The operator opens the hopper access door - at shoulder height - and unties the outer flap and outlet spout tie to enable flow.
- The operator closes the hopper access door and initiates the hopper vibration sequence to induce flow.
Hopper Style Big Bag Unloader Ergonomics and Safety
The hopper makes a hopper style bulk bag discharger inherently safe. Since the entire weight of 
the bulk bag is safely supported by the hopper and the discharger is designed so that the operator interfaces with its access door at shoulder height, operators never work under a suspended load and the reach into the hopper to untie the outer flop and outlet spout is easy and strain-free.
The hopper style bulk bag discharger's design couldn't be more simple or effective when it comes to ergonomics and safety!
Hopper Style Bulk Bag Discharger Dust Containment
Standard hopper style bulk bag dischargers provide excellent dust containment without having to resort to outlet spout clamps. Three factors provide this level of dust containment performance:
- Dust membrane. As the bulk bag is lowered into the hopper it passes
through and seals with a rubber (or Nitrile in food applications) membrane that seals with the sides of the bulk bag. When the big bag is fully seated in the hopper the membrane has created a sealed enclosure within the hopper.
- Hopper outlet. Hopper style bulk bag dischargers are designed such that the big bag’s outlet spout protrudes through the circular hopper outlet during discharge. Plus, the diameter of the hopper outlet is slightly less than the outlet spout diameter and that means the bulk bag’s outlet spout seals against hopper’s outlet preventing blowback into the hopper once a flood feed condition has been reached. This also means that the ingredient exits the outlet spout below the hopper not in it as with paddle style bulk bag dischargers.
- Dust vents. Dual dust vents that can be connected to a vacuum dust
collections system allow the sealed hopper to be maintained at negative pressure. Therefore, any dust particles present in the hopper are extracted. Operators can open the hopper access door during discharge and no dust will escape!
No moving parts, no clamps, no need for integral dust collection. Hopper style bulk bag unloaders feature a simple, but extremely effective design that provides outstanding dust containment performance.
Hopper Style Big Bag Unloader Flow Inducement
One again, the hopper style bulk bag discharger’s simple design provides excellent performance in this case with flow inducement. Two factors enable superior flow inducement:
- Hopper shape. When the big bag is seated in the hopper it will have
‘taken’ the shape of the sloped sides of the hopper style big bag unloader. This promotes flow just as the conical bottom does in a bulk hopper.
- PULSED vibration. If the product requires further inducement to achieve a steady flood feed state at its outlet, an electromechanical (or pneumatic) vibrator mounted to the hopper provides additional flow inducement. The vibrator’s duty cycle - the amount of time it runs and the amount of time between when it runs e.g. 15 seconds on and 10 seconds off) provides just enough energy to maintain a flood feed condition at the outlet. The vibration amplitude and duty cycle is adjusted during commissioning to ensure consistent inducement.
Over the past two decades and more our experience with hopper style bulk bag dischargers are that if the ingredient is capable at all of flowing, the combination of the steep sloped hopper and vibration will get ANYTHING to flow from a bulk bag.
Hopper Style Bulk Bag Discharger Outlet Spout Clamps
Control and Metering patented a bulk bag outlet spout clamp design in the early 1990s. Within a
few years we realized that while the outlet spout clamp eliminates dusting during the onset of ingredient flow and during discharge, dusting would occur when the clamp was lifted and the empty bulk bag was removed from the discharger.
As a result, we designed our Iso Flo hopper style bulk bag discharger that encloses the outlet spout clamp in a negatively pressurized isolation chamber. This design has been effectively used in pharmaceutical plants, food plants and for handing hazardous ingredients.
The key considertation is that, unlike paddle style bulk bag dischargers, hopper style big bag unloaders do not require outlet spout clamps to try and solve ergonomic, safety and dusting problems.
Hopper style bulk bag dischargers are inherently simple in their design and use and provide excellent performance in all aspects of bulk bag discharging.