A tie-string discharge spout is an all-or-nothing device. Once it is untied over a hopper, the bag empties. That is fine when the whole bag goes into one batch, and a problem the moment a process calls for two-thirds of a bag now and the rest on Thursday — because the only way to stop the flow is to re-tie a spout that is under load, by hand, with product running.
A hose slider is the answer to exactly that. It is a rigid bar or collar that slides across the discharge spout and pinches it closed against itself, and slides back to release. India Pack's FAQ describes it as a closure mechanism for regulating or fully stopping flow through the discharge spout, giving the operator control when a bag is only partly emptied.
What it does that a tie-string cannot
Three things, all of them operational rather than structural.
Stop a flow that has already started. The slider is actuated from outside the spout, with the bag suspended and product moving. Re-tying a cord under those conditions is not a comparable option.
Re-close and move a part-used bag. A bag pinched shut by a slider can be set down, stored and lifted again. This is the case that justifies the accessory on its own: partial draw-down without decanting the remainder into something else.
Meter the rate. Sliding the bar part-way throttles the aperture, which matters where a downstream weigher or mixer cannot take a full-bore dump.
Bag-side closures versus equipment-side flow control
This is the distinction that causes most of the confusion in enquiries, and almost nobody separates the two.
A hose slider, a B-Lock cord lock, a tie string, a petal closure and a protective flap are all part of the bag. They travel with it, work in a yard or a warehouse, and cost a few units of bag price. An iris valve, a pinch valve, a clamp ring or a telescoping discharge tube are part of the discharger — the frame the bag is hung in. They are capital equipment, they are usually better at dust control, and they do nothing for a bag that is not currently in the frame.
Buying a discharger with an iris valve does not give you the ability to close a part-used bag and put it back on the rack. That is a bag-side job, and the slider is the bag-side device for it.
The options compared
| Closure / device | On the bag or the equipment | What it does | Re-closable | Partial discharge |
|---|---|---|---|---|
| Tie string / rope cord | Bag | Gathers and ties the spout shut for transit | Only by re-tying, unloaded | No |
| B-Lock (cord lock) | Bag | Locking device on the spout tie-strings | Yes, by hand | Limited |
| Hose slider | Bag | Rigid bar or collar pinches the spout closed | Yes, under load | Yes |
| Petal closure | Bag | Segmented spout that opens outward when untied | No | No |
| Protective flap / sewn cover | Bag | Covers the spout against contamination | Yes | No — not a flow device |
| Iris valve | Equipment | Diaphragm aperture opened progressively | n/a | Yes, in the frame |
| Pinch valve | Equipment | Pneumatic pinch on the spout | n/a | Yes, in the frame |
How to specify it
- Spout diameter and length. The slider has to match the spout it closes, and spout dimensions are custom on most bags.
- Whether a liner is fitted, and how it is attached. A slider on a lined bag pinches liner and fabric together, so liner geometry and attachment are part of the question — see FIBC liner attachment methods.
- Product flow behaviour. Free-flowing powders throttle predictably; cohesive or bridging materials may need a conical discharge rather than a restriction added to a straight spout.
- Static protection type, if the product is combustible. Type C bags use conductive threads and must be grounded in use; Type D uses static-dissipative fabric and needs no grounding connection. Any rigid component added to the discharge point has to be assessed within that scheme, from the safety data sheet.
Send those with your request for quote.
FAQ
Q: What is a hose slider on an FIBC? A: A rigid bar or collar that slides across the discharge spout and pinches it shut, and slides back to release. It lets an operator stop or throttle the flow of material from a bag that is only partly emptied.
Q: Can a hose slider close a bag that is already discharging? A: That is its purpose. It is actuated from outside the spout while the bag is suspended and product is moving, which a tie-string cannot be.
Q: Is a hose slider the same as an iris closure? A: No, and the difference is where they live. A hose slider is part of the bag and travels with it. An iris valve is part of the discharging equipment the bag is hung in. Only the slider can re-close a bag that has left the frame.
Q: Does a hose slider work on a lined bag? A: It pinches liner and fabric together, so the liner's geometry and attachment matter. Raise it at specification stage rather than discovering the interaction on the line.
Related reading
- FIBC liner attachment methods
- Spout / discharge spout FIBC bags
- Open top with discharge spout FIBC bags
- India Pack FAQ
- Request a quote
Sources
- India Pack — FAQ, "What is a Hose Slider in an FIBC?" (closure mechanism used to regulate or completely stop the flow of materials through the discharge spout; slides a rigid bar or collar over the spout to pinch it shut; precise control when partially emptying a bag). Same page: the B-Lock / cord lock definition, and the Type C grounding versus Type D static-dissipative distinction — https://www.indiapack.co.in/faq-s-frequently-asked-questions
- Understanding FIBC bag discharge options (spout bottoms closed with a safety tie or rope cord; iris closure controlling discharge flow) — https://codefine.com/blog/products-and-materials/understanding-fibc-bag-discharge-options/
- Bulk bag dischargers (clamp rings creating a dust-tight connection to the discharge spout; telescoping tube maintaining an open spout; flow control valve pinching the spout — all mounted on the discharger frame rather than the bag) — https://flexicon.com/bulk-handling-equipment-and-systems/bulk-bag-discharger/
- Bulk bag dischargers, unloaders and FIBC dumpers (discharge system comprising support frame, bag spout interface with flow control valve, dust containment enclosure and flow-aid devices) — https://www.nbe-inc.com/processing-systems/bulk-bag-dischargers