Bulk Bag Unloader Ultimate Buying Guide

Throughout the industries, more and more manufacturers invest in bulk bag unloading systems to improve efficiency in powder processing. This article aims to present the basic principles, structures and available features and help you make an informed decision.

1. Introduction of Bulk Bag

Bulk bags (also known as FIBCs, big bags, jumbo bags) are large bags used for storing and transporting dry solid products. A technical term of bulk bag is “FIBC”, which stands for flexible intermediate bulk container. Most bulk bags are made from 100% virgin woven polypropylene. Bulk bags typically hold about 500kgs-2500kgs of product.


Here are some typical dry solid materials:



PlasticsABS resinBakeliteEpoxy ResinNylonPolypropylene
EnvironmentalActivated carbonDry SorbentFly ashSoda Ash 
Animal feedAmino acidBranGlutenSaltYeast extract
ConstructionCementGypsumIron OxidePigmentTalc

Advantages of FIBC bulk bags:

  • FIBC bags are very strong and safe and it can carry up to 1000 times its own weight.
  • FIBC bags are simple to use and transport.
  • FIBC bags are recyclable and reusable.
  • FIBC bags can come in any size as per requirement.
  • FIBC bags are cost effective and environmental friendly.

Thanks to these advantages, 42 million bulk bags are used annually in the world nowadays. Over the past decade, the use of bulk bags has increased steadily, with a yearly growth rate of approximately 15 percent.

2. What Are Bulk Bag Unloaders?

Bulk bag unloaders are also commonly known as bulk bag dischargers, big bag dump stations, big bag discharge stations, FIBC dischargers, and FIBC unloaders. A bulk bag unloader is a stand-alone system which provides a convenient, safe, dust-fee method for handling and discharging bulk bags.

bulk bag unloader

3. Basic Structures of Bulk Bag Unloaders

A typical bulk bag unloader could be divided into six parts – support frame, bag lifting mechanism, flow aid device, bulk bag spout interface, downstream process system and electric controls.

Bulk Bag Unloader Structure

3.1 Support Frame

The support frame of a bulk bag unloader could be designed according to the specific bag size and the bag loading method. A large size bulk bag commonly requires a support frame with a higher or wider dimension. And the restrictions at the location such as ceiling height will also be evaluated to determine the dimensions of the support frame.

 Bulk bag frame

The whole framework is constructed from welded carbon steel or stainless steel structural tubing. Wild steel protection includes epoxy coating, spray painting or powder coating to the specific need. Nickel-chromium alloys, also known as stainless steel 304 and 316, are suitable for most classes of food and chemical production.

3.2 Bag Lifting Mechanism

The first step of bulk bag handling is to locate the bulk bag at a proper position. There are four possible lifting methods of bulk bag – forklift, integrated electric hoist, separate lifting hoist, column lifter.

3.2.1 Forklift

A forklift is a powered industrial lifting equipment wildly used to lift and move materials over short distances. Typically in a height restricted headroom, the bulk bag securely held under a bag lifting adapter is loaded and ready to discharge via a fork truck. Sometimes the adjustable bag receiver arms allow easy entry and quick size change different bag heights.


3.2.2 Integrated Electric Hoist

An electric hoist/trolley assembly provides the most popular pick-up method of bulk bag loading. Electric hoists can be ordered with either a 1-ton or 2-ton capacity, depending on the size of bulk bags being used.

Integrated Electric Hoist

The integral trolley rides on a slide beam that is centered over the frame. The bulk bag is attached to a bag hanger for raising and positioning the bag into the support frame. The bulk bag with its hanger is chain-hoisted, lifted from the floor level, moved and lowered for docking.

3.2.3 Overhead Lifting System

Sometimes customers may ask using their existing overhead lifting systems such as overhead traveling bridge crane, gantry crane or monorail for handling and transporting their bulk bags. In these circumstances, a low-profile bulk bag unloader eliminates upper frame components and minimizes weight for in-plant mobility and feasibility.

Overhead Lifting System

3.2.4 Column Lifter

A Column lifter provides a GMP, ergonomic, and portable solution for lifting, transporting, and positioning bulk bags. Thanks to the high grade surface finish and the free accessibility, lifting columns are especially suitable in a clean room applied in pharmaceutical, food and fine chemical industries.

Column lifter

3.3 Flow Aids

Flow aids may be defined as devices that stimulate or improve bulk solids flow out of bulk bag storage. Many flow aid devices are necessary to promote the material discharging while some bulk materials may become agglomerated or severely case hardened.

3.3.1 Vibration Pan

A large pan is design to hold the bulk bag and induce material flow through the discharge spout induce material flow through the discharge spout continuously. Single or dual exciters can be used to impart vibrations. The entire assembly oscillates in a horizontal plane at frequencies ranging from 10 to 50 Hz and amplitudes ranging from 1.5mm to 12mm.

Vibration Pan

3.3.2 Bag Massage Unit

Almost every bulk bag unloader manufacturer provides bag massage units as aid devices to facilitate material emptying. They are operated by pneumatic cylinders in forms of bag massage paddles, plates or frames placed on the bottom pan or lateral frames.

Bulk bag massage

Bag Massage units are especially effective when the storage in bulk bags cause problems with compressed materials. Commonly they are programmed to operate in a sequence which best suits the particular application for maximum performance.

3.3.3 Bulk Bag Conditioner

Sometimes materials like hygroscopic chemicals and heat-sensitive products are prone to solidification during storage and shipment. Traditional flow aids become are inefficient or completely ineffective to loose loosen bulk solid materials.

Bulk Bag Conditioner

A bulk bag conditioner features two hydraulic rams with specially-contoured end plates that press opposite sides of bulk bags. Each ram driven by hydraulic cylinder that provides the force to effectively crush severely agglomerated materials into smaller chunks.

3.4 Bulk bag spout interface

The operator interface is the key device used in conjunction with the downstream process when unloading the bulk bag. The specific design of the spout interface depends on the bulk bag style and dry material flow characteristics.

3.4.1 Untie Box

The untie box, also known as access chamber, provides a safe and ergonomic access to the spout of the bulk bag. The dust-tight access door on the face of the untie box is hinged and held secure with heavy-duty quick release clamps. Typically the top of the untie box is flanged for connection to a flow control valve while the bottom is flanged for connection to the downstream process equipment.

Bulk bag spout Untie Box

3.4.2 Iris Flow Valve

The iris valve is a lightweight, compact device typically installed on bulk bag unloaders, bin bottoms, and chute outlets. The iris valve closes off the bulk bag’s spout without directly contacting the flowing material, while in other applications the valve directly contacts the material. The iris valve can be manually, pneumatically, or electrically driven. With the twist handle, the operator rotates the handle to control the valve’s opening in an infinite number of positions across the 180-degree arc.

iris valve

3.4.3 Pinch Flow Valve

A pinch flow valve is also a great alternative specifically for bulk bag spout control. It would appear to allow quicker and easier clasping of the bag than the conventional iris valve. The pinch valve is commonly pneumatically operated by 2 opposite cylinders. The pinch valve is positioned under the vibrating hopper and stops the flow during big bag emptying.

Pinch Flow Valve

3.4.4 Clean Docking Device

The clean docking device with a double ring and lever mechanism allows dust-free connection and emptying of bulk bags. When the bulk bag is positioned on the right position via a lifting hoist, the outlet spout is pulled over the inner ring by the operator. Then close and clamp the upper disc manually or pneumatically and unite the string of the bulk bag. The double pipe design and prevents material spillage when untying, retying, or removing an empty bag.

Bag Spout Docking Device

3.4.5 Piercing Knife

A piercing knife is specially designed for disposable single trip bags without bottom spout.

Piercing Knife

When the bulk bag is lowered into the place, a static or pneumatically actuated knife assembly pierces the center of bulk bag to allow the material to discharge. Meanwhile an outlet extraction collects dust during bag piercing operation.

3.5 Downstream Process Interface

A wide range of configurations are available to integrate the bulk bag unloader with downstream process equipment. The specific working system depends on the material characteristics and the process requirement such as sieving, milling, mixing, feeding and pneumatic conveying etc.

3.5.1 Surge Hopper

A surge hopper is typically mounted below the bag spout interface for intermediate material storage from the bulk bag. The surge hopper is designed in round, square, rectangle to work properly with the existing equipment or other processing system.

Surge hopper

3.5.2 Screw Feeder

A screw feeder combined with a hopper provides a constant flow of dry material either in continuous or batch production. For the success of your application, several factors must be considered when designing or selecting a suitable feeder.

screw feeder

No screw feeder design can handle all the different material characteristics or throughput requirements. Single Screw Feeders are available to handle free-flowing materials; twin screw feeders are for more difficult materials.

3.5.3 Vacuum Conveying

Vacuum conveying systems are also widely used for transport powders, granules and most bulk solid material with few moving parts. Typically the surge hopper is equipped with a vacuum inline pipe or suction lance, and the material will be vacuum conveyed to the destination point.

vacuum conveying

As a totally enclosed system, it is particularly important for the handling of toxic and explosive materials or any material where environmental considerations have to be taken into account.

3.5.4 Pressure Conveying

For dilute phase pressure conveying, a rotary valve or venturi educator meters the material into the air stream. The non-abrasive materials are conveyed to several reception points from one pickup point at a high rate.

Dense Phase Pressure Vessel

Dense phase pressure conveying is suitable for gently conveying abrasive materials over long distances. The material dumped from the bulk bag is loaded into a pressure vessel and transported to the destination. Most systems include several air control valves and the high pressure compressed air supply.

3.5.5 Flexible Screw Conveyor

A flexible screw conveyor is suitable for routes of less than 10 m and can also convey at any angle. The inlet of the transition hopper is connected to the bag spout interface while the discharge is connected to the flexible screw conveyor.

Flexible Screw Conveyor

3.5.6 Tubular Drag Conveyor

Tubular drag conveyors use discs attached to a metal chain to pull wet or dry material through the conveyor to the discharge point. The drag conveyor inlet is connected to the flanged outlet of the transition hopper of the bulk bag unloader. And the bulk solid materials including fine powders, granules, pellets, are gently transferred to the final discharge point.

Tubular Drag Conveyor

3.6 Equipment controls

Every bulk bug unloader supplier provides a complete control system to meet your exact specifications and functionality. Due to the process complexity and the specific request, the control systems can be designed and employed with manual or fully-automatic functionality.

3.6.1 Electrical Chain Hoist Pendant

The multi-button pendant switches are ideal for operating a hoist to lift, position, and lower the bulk bag with one person from the floor. Typically an ergonomic pistol grip is offered for simple hoist applications. In some cases, radio controls for an overhead crane system are available for remote operation.

3.6.2 Manual Controls

For individual equipment, manual or semi-automatic control cabinets are designed to complete the bulk bag unloading sequence of operations. The cabinets are equipped with push buttons, selector switches, pilot lights, measurement instruments. They are commonly mounted on the frame with the fixing brackets.

Manual Control for bulk bag discharge

3.6.3 Fully Automatic Controls

PLC controls are employed to monitor and control sophisticated systems such as bulk bag batch weighing and dosing etc. Human-machine-interfaces with touch screens serve to display the actual operating conditions of the plant process.

Tasks that are typically automated include lifting and positioning bulk bag, vibrating bag, docking bag, closing slide gate, starting and stopping downstream conveyors, buffer hopper weighing, screw feeding etc.

4. Typical Bulk Bag Unloading Application

Bulk Bag Unloaders come in all shape and sizes, and different models are available to accommodate the specific needs of the discharging application.

4.1 Low Profile Bag Discharge

These bulk bag unloaders are designed as a simple discharging system to fit restricted areas and low headroom. The unloader provides overhead space for suspending of bulk bags using an existing slide beam and electric hoist or a forklift.

Low Profile Bag Discharge

When the bulk bag is placed on the support pan, the operator can access and untie the bottom spout. The discharge interface of the chute is custom made to fit the specific application. And a removable upper frame can be made if necessary.

4.2 Forklift Loaded Bag Discharge

The forklift style discharger consists of a steel framework, massage paddles, a bag spout access box and a fork style pickup device. The bulk bag is secured by the pickup device and introduced into the frame of the discharger. The bag support frame is adjustable to an appropriate height for the bulk bag being utilized.

Forklift Loaded Bag Discharge

The product flow is optimized by a pneumatic massage system or a vibrating plate. The bulk bag spout interface could be a pneumatic docking device or a untie box.

4.3 Bulk Bag Discharge and Manual Sack Dump Combination

This station is designed for automatic discharge from bulk bags as well as manual emptying from sacks, drums or other containers with different sizes. The bulk bag is positioned and docked via a clean docking mechanism. Optional bag massagers or vibration support pan can promote material discharge for products with poor flow characteristics.

Combined bulk bag discharge

Sacks and drums are placed onto the operator desk and emptied to the downstream process. It is a reliable and flexible station for materials from sacks and FIBCs into a closed system.

4.4 Bulk Bag Unloading for Vacuum Conveying

Vacuum conveying provides a hygiene and flexible transferring method for food, pharmaceuticals and chemical products. The pneumatic system also can feed several receiving points from a single bulk bag.

Bulk Bag Unloading for Vacuum Conveying

Below the bag spout interface, a surge hopper connected with inline vacuum pipe or suction pipe directs the material to the vacuum receiver hopper. At the end of the timed sequence the discharge valve can open and the material conveyed will discharge in to the next process.

4.5 Bulk Bag Unloading for Batch Weighing

The precise combination of several major and minor ingredients is the key to effective batch production. Major raw materials need to be discharged from bulk bag and accurately weighed prior to an initial mixing operation.

Bulk Bag Unloading for Batch Weighing

The batch weighing system is designed and engineered based on the material characteristics, process formulation, weighing accuracy requirement. Typically a surge hopper and a dosing screw are coupled with the bag unloader for precise feeding.

4.6 Bulk Bag Unloading with Glove Box

A bulk bag discharge system with a glove box is designed to allow operators to handle toxic or fine products without being in contact with them. Using gloves, the bag spout is untied within an enclosed system. Inside the glove box isolator, the products are discharged into the feeding hopper for transfer by the vacuum conveyor. After discharge, the bag spout can be retied using the gloves, thus preventing any residual material from escaping when the FIBC is disconnected.

Bulk Bag Unloading with Glove Box

5. Features Options

We have described the basic modular structures of bulk bag unloaders as above. There are also a wide range of featured options for the customized bulk bag handling applications.

5.1 Dust Collection

Dust control is a key feature of any sack emptying or bulk bag discharge process. An integrated dust collector is offered as a simple method for safety and hygiene requirement. It prevents dust escaping during the entire discharging sequence with pulse jet filters. Sometimes the dust is extracted to the central dust collection system with a port connection.

Integrated Dust Collector

5.2 Explosion Risk Prevention

Some customers may be faced with dust explosion challenge when handling combustible powder material. Once the explosive properties of the material are known, processing equipment can be configured to mitigate the risk.

For example, a pneumatically hoist rather than an electrical hoist can be operated to eradicate ignition source. Finely polished static parts in contact with the product generate no heat. Appropriate protection measures can be taken to meet ATEX regulation.

5.3 Size Reduction Equipment

Unwanted agglomeration is a nature phenomenon for many materials during storage and shipping. The well processed material is asked at the beginning of the entire process before mixing, reacting, conveying etc.

Versatile size reduction equipment items such as lump breakers, material agitators can be designed in an inline operation at the discharge point of the raw material.

5.4 Integrated Sifting

Screening systems ensure no foreign bodies, raw material impurities, or packaging remnants remain in the product. Typically vibratory screeners and centrifugal sifters can be fed with bulk bag discharge for safety production. The centrifugal sifter not only screens out any impurities, but also breaks lumps in all types of products. A rotary valve is commonly employed prior to screening process.

Centrifugal Sifting

5.5 Load cells for Weighing

Depending on the specific requirement, load cells can be installed at the equipment base to monitor the weight loss out of the bulk bag discharger. The data from each load cell can be collected and streamed through a summing box to a digital display. The PLC controller checks the batch weight and determines whether or not to feed the next process.

5.6 CIP Sanitization

It is crucial to avoid cross contamination in food, beverage and pharmaceutical production when changing products. CIP systems offer efficient and reliable cleaning with minimal downtime. When it comes to bulk bag discharge, crevice free self-draining interior design with rotary nozzles and vent are available for optimum cleaning efficiency. The bag spout clamping device can also be conjunct with hot air drying units.

CIP Cleaning

5.7 Liner Tensioning

During latter stages of discharge, some poor-flowing materials may not fall through the outlet spout consistently. The liner tensioner is designed to overcome this problem with minimal operator intervention especially used in forklift loaded bag discharger. The bulk bag is gradually lifted and stretched via a pneumatic or spring loaded tensioner for total emptying of bag contents.

5.8 Adjustable Frame Height

Some customers ask the equipment is adjustable in height to suit varying bulk bag sizes. The telescopic columns are typically equipped with the forklift style bag dischargers, and have several height settings to accommodate bulk bags of different lengths.

5.9 Mobile Frame

The custom-made mobile frame provides a flexible discharge arrangement, especially in facilities with limited area. The welded mobile base is specifically made to fit existing overhead lifting system in order to provide convenient utilization at multiple locations.

Mobile bulk bag frame

5.10 Access Platform and Stairs

Industrial metal stairs and handrails are necessary for access to a work platform and bulk bag operation. Custom platforms are made of stainless steel, lightweight aluminum, and carbon steel for long lasting durability.

6. Top Considerations Before Buying a Bulk Bag Unloader

A bulk bag unloader is far more than equipment for discharge bulk material as stated above, and it is important part of a whole process system. Before you choose a bulk bag unloader, consider the following questions to determine what features it needs.

6.1 What is your industry application? Do you need any sanitary compliance?

In pharmaceutical, food and fine chemical industry, stainless steel is often used as parts in contact with products. Sanitary construction materials provide an easy and thorough cleaning and repeated use without cross-contamination. Defining what material to be used and what surface finishing to be employed can be a major factor in the total cost of a bulk bag unloading system.

6.2 What is the size of the bulk bag? What is the weight of the bulk bag?

Although there are several standards for the use of FIBC, the dimensions of bulk bags are different from each other. The height of the bag and the extent to which it stretches when lifted, is very important to confirm. It is necessary to define the maximum weight capacity in the very beginning.

Bulk bag size

6.3 Is the bag a single trip bag or a reusable bag?

Single trip bulk Bags are suitable for low value products or long time storage within plant environments. In this condition, a piercing knife is suitable to cut the bag bottom without wastage or spillage.

6.4 How do you want to load the bulk bag into the discharge frame?

Lifting the bag and positioning it on a support frame is the initial step when bulk bag handling. Make sure to communicate with the supplier and confirm which lifting method you plan to use so that the discharger can be designed to accommodate this method.

In addition, it may be difficult to raise and lower the bulk bag using a dedicated hoist or a column lifter in a height restricted room. A low profile style discharge will be a better choice for these low-headroom applications.

6.5 How to obtain reliable flow when discharging material?

Flow aids such as pneumatic bag massagers or a vibratory base are commonly equipped with bulk bag dischargers to handle poorly flowing materials. In particular, a bulk bag conditioner returns severely hardened bulk material to free-flowing state as mentioned above.

6.6 Do you have any explosion protection requirement?

During some sensitive material process, it may generate combustible dusts. The properties of the materials being handled must be understood and measured accurately and then appropriate measures can be implemented into the process. To protect against workplace injuries, damage to facilities, the bulk bag unloading system with explosion proof must meet ATEX94/9/EC directive.

6.7 How will the discharger contain and control dust?

If you have an existing industrial duct collection system in you plant, a dust extraction port is commonly used and connected to the central system.
An integrated dust collector is also an option that prevents the escape of dust throughout the entire discharging process.

6.8 Do you need any containment solutions?

A contained system provides perfect protection against toxic and highly active products other potentially dangerous materials. A glove box isolator can be integrated with the bulk bag discharge system untying bags preventing operator exposure to hazardous product in a closed cabinet.

6.9 What is the downstream process?

Versatile conveying and feeding methods are available to connect to your existing equipment or other process system. Fully understanding the process and control requirement is critically important to provide an ergonomic design and operation.

6.10 How to find a quality bulk bag unloader manufacturer?

Every material has different handling characteristics. There is no universal bulk bag unloader that is suitable for all the material within different conditions. You need proven methods by an experienced supplier to assure you that your process will run smoothly to maximize uptime.

Our rich experience in bulk solids handling assure you that we have the expertise to design a system to meet your special requirements.

By | 2019-08-22T06:01:02+00:00 December 21st, 2017|Blog|Comments Off on Bulk Bag Unloader Ultimate Buying Guide