How a bag empties matters just as much as how it fills, and for processes that need controlled, metered discharge rather than a single full dump, bottom construction becomes a functional part of the process equipment rather than just packaging. This guide compares the main FIBC bottom discharge types, explains how an Iris closure provides adjustable flow control, and covers what to specify when matching discharge design to downstream equipment.
Why Bottom Construction Matters as Much as the Top
The bottom of an FIBC bag carries the full weight of the filled product and, for bags with a discharge spout, also controls how that product exits during processing. A mismatch between discharge type and downstream equipment can slow production, create dust exposure, or make precise dosing impossible, all of which are operational problems rather than packaging defects once the bag is already in use.
Read more: FIBC Top Filling Options: Choosing the Right Top Spout Size
Common FIBC Bottom Discharge Types
Flat Bottom (No Discharge)
A flat bottom has no dedicated discharge opening, meaning the bag is emptied by cutting it open or tipping the entire contents out at once. This is the simplest and most economical bottom construction, suited to applications where the bag itself is not reused and controlled discharge is not required.
Spout Bottom
A spout bottom mirrors the spout top configuration, providing a defined discharge opening that can connect to a hopper or chute below. Flow through a standard spout bottom is generally an open or closed condition, either flowing freely once untied or fully sealed, without fine control over the rate of flow.
Iris Closure
An Iris closure uses a diaphragm mechanism, similar in principle to a camera aperture, built into the discharge spout to allow the opening to be adjusted rather than only fully open or fully closed. This design allows an operator to control discharge rate and even pause flow mid-discharge without fully closing and re-securing the spout, which is useful for metered dosing or controlled feed into downstream processing equipment.
How an Iris Closure Works
The diaphragm fabric is sewn into a ring at the discharge opening with an adjustable drawstring or mechanical collar that changes the effective opening diameter. Narrowing the diaphragm restricts flow to a controlled trickle, while opening it fully allows unrestricted discharge, giving operators a single adjustable point rather than needing to swap discharge hardware for different flow requirements.
Iris Closure vs Standard Spout: Flow Control Differences
A standard spout bottom is adequate when the goal is simply emptying the bag completely into a receiving hopper, since flow rate is not adjustable once the spout is open. An Iris closure is the better choice when a process requires controlled or metered discharge, partial emptying with the ability to reseal, or precise dosing into batch processing equipment. The added mechanical complexity of an Iris closure increases cost compared to a standard spout, so the choice should be based on actual process requirements rather than defaulting to the more capable option without a clear need.
Read more: Anti-Static Bulk Bags: How a Type C Bag Prevents Ignition Risk
Discharge Spout Closure and Sealing Methods
Tie-Off
The simplest closure for a standard spout bottom, gathering and securing the fabric with cord or tape, offering no flow control beyond fully open or fully closed.
Clamp Closure
A reusable clamp compresses the spout fabric for a tighter seal than a tie-off, useful for repeated open and close cycles during multi-stage discharge operations.
Iris Diaphragm Seal
The Iris mechanism itself functions as both the flow control and the seal, closing fully when adjusted to its minimum opening while still allowing fine control at intermediate positions, which is the core advantage over tie-off or clamp closures that only offer open or closed states.
Matching Discharge Type to Downstream Equipment
Discharge spout diameter and closure type need to match the receiving hopper, feed screw, or processing equipment the bag will connect to, in the same way top spout diameter needs to match filling nozzles. Buyers integrating bags into an existing process line should provide the receiving equipment’s connection dimensions to the bag manufacturer, and for Iris closure applications, confirm whether manual or equipment-actuated adjustment is required.
Read more: Sift Proof FIBC Bags: Building a Truly Leak Proof Jumbo Bag
Specification Details for FIBC Bottom Discharge Types
- Bottom type, specifying flat bottom, spout bottom, or Iris closure based on the discharge process required.
- Discharge spout diameter, matched to receiving equipment connection dimensions.
- Closure method, confirming tie-off, clamp, or Iris diaphragm mechanism.
- Fabric reinforcement around the discharge opening, since this area experiences repeated stress during open and close cycles on multi-trip or process-integrated bags.
- Liner compatibility and whether the liner requires its own separate discharge closure integrated with the outer spout.
How Tam Tam Packaging Configures Bottom Discharge to Order
Tam Tam Packaging manufactures spout bottoms and Iris closure discharge configurations to the buyer’s specified dimensions, confirming compatibility with downstream receiving equipment before production. Reinforcement around the discharge opening is specified according to expected trip count and cycle frequency, so the discharge point holds up under repeated use rather than wearing prematurely.
Common Mistakes When Specifying Bottom Discharge Types
- Ordering a standard spout bottom for an application that actually requires the metered flow control an Iris closure provides.
- Specifying an Iris closure for simple full-dump applications where the added cost provides no operational benefit.
- Not confirming discharge spout diameter against actual receiving equipment dimensions before ordering.
- Overlooking reinforcement needs for discharge points used across multiple open and close cycles.
- Failing to coordinate liner closure with outer spout closure, resulting in two separate discharge points that do not empty in sync.
Applications in the Chemical Industry
Chemical processing operations frequently require precise, metered discharge into batch mixing or reaction equipment, making Iris closure bottoms a common specification for powders and granules that need controlled dosing rather than a single full-volume dump. Standard spout bottoms remain common for chemical products moving to bulk storage silos where full discharge in a single operation is the actual requirement, illustrating why discharge type should be matched to the specific downstream process rather than treated as a universal upgrade.
Frequently Asked Questions
What is an Iris closure on an FIBC bag?
It is a diaphragm-based discharge mechanism that allows the bottom spout opening to be adjusted for controlled flow, rather than only being fully open or fully closed like a standard spout.
When should I choose an Iris closure over a standard spout bottom?
When the process requires metered or controlled discharge, partial emptying with resealing, or precise dosing into batch equipment, rather than a single full-volume dump.
Does an Iris closure cost more than a standard spout?
Yes, due to the added mechanical complexity, so it should be specified based on an actual process requirement for flow control rather than as a default upgrade.
Can a flat bottom bag be used with automated discharge equipment?
Generally no. Flat bottom bags have no dedicated discharge opening and are typically emptied by cutting or tipping, making them unsuitable for automated discharge systems.
How do I know what discharge spout diameter to order?
By providing the manufacturer with the receiving equipment’s connection dimensions, whether a hopper, feed screw, or another interface, rather than requesting a generic standard size.
Conclusion
FIBC bottom discharge types, from flat bottom through standard spout to Iris closure, should be matched to the actual downstream process rather than chosen by default. An Iris closure earns its added cost when a process genuinely needs controlled, adjustable flow, while a standard spout or flat bottom remains the practical choice for simpler full-discharge applications.
Tam Tam Packaging Co. configures bottom discharge type and spout dimensions to match your downstream equipment, including Iris closure options for controlled flow applications. Contact our team to confirm the right discharge specification for your process.
Contact Us
Tam Tam Packaging Co.
Email: sales@tamtamjumbo.com
Website: https://tamtamjumbo.com/
WhatsApp: +84 92 852 3288
Read more
FIBC Bottom Discharge Types: How an Iris Closure Controls Flow
How a bag empties matters just as much as how it fills, and for processes...
Jul
FIBC Top Filling Options: Choosing the Right Top Spout Size
The top of an FIBC bag does more work than it gets credit for. It...
Jul
Bulk Bag Stitching Type: How Sewing Machine Choice Affect Seam
Fabric weight gets most of the attention when buyers evaluate FIBC bag strength, but the...
Jul
Moisture Proof FIBC Bags: What Triple Proofed Actually Combines
Hygroscopic powders absorb ambient moisture whenever the packaging around them allows it, and for many...
Jul
FIBC Fabric GSM Guide: How Fabric Weight Determines Strength
GSM is the number buyers reach for first when comparing FIBC fabric across suppliers, and...
Jul
Breathable FIBC Bags: Guide to Choosing the Right Mesh Big Bag
Buyers moving from small mesh sacks to bulk mesh big bags for the first time...
Jul