Reject method comparison
Air blast, pusher, sweep arm, lane diversion, drop flap and retracting belt—what each method does and which production variables change the answer.
Selection starts with the real productChoose the method from the product’s weight, stability, fragility and spacing, then check it against line speed, available conveyor length, reject destination and the consequence of a failed reject. Product trials are advisable where behaviour is uncertain.
No reject mechanism is universally best. A light, sealed sachet may respond well to an air blast; a stable carton may suit a pneumatic pusher; fragile or closely spaced packs may benefit from a controlled diverter; and compact products on a suitable conveyor can be removed through a drop flap or retracting section.
This table is a starting point, not a final design rule. The complete product range and worst operating condition still need review.
| Reject type | Typical starting point | Key checks | Common destination |
|---|---|---|---|
| Air blast | Suitable lightweight packs at controlled pitch | Surface area, air supply, pack stability, adjacent products | Chute or guarded catch area |
| Pneumatic pusher | Stable cartons, containers and packs that tolerate contact | Mass, cycle time, stroke, guide rails, recovery time | Secure bin or side conveyor |
| Sweep arm / diverter | Products needing more controlled lateral redirection | Product length, pitch, entry angle and lane width | Reject lane or rework conveyor |
| Drop flap | Compact, stable products with suitable conveyor geometry | Available drop zone, flap timing, transfers and guarding | Bin or chute below |
| Retracting belt | Applications needing a rapid controlled gap | Product length, belt speed, fall path and mechanism cycle | Bin or chute below |
| Stop and alarm | Products that cannot be safely ejected automatically | Line clearance, operator response and quality procedure | Manual controlled removal |
A timed compressed-air jet moves a suitable product laterally. It can be fast and mechanically simple, but needs adequate product surface area, predictable spacing, controlled air pressure and a defined catch path. Very heavy, open, unstable or easily disturbed packs may be poor candidates.
A guided face extends across the conveyor to move a product into a chute, bin or parallel conveyor. It provides positive contact and can suit stable products, but the stroke and return must complete before the next product reaches the reject zone.
A moving guide redirects the product over a longer path. This can reduce impact and create separate reject, rework or sample lanes. Product length, entry angle, guide-rail position and close pitch are important.
A conveyor section opens so the failed product falls into controlled containment below. The product must cross the opening cleanly, while the flap geometry, cycle time and guarding must suit the complete range.
A belt or conveyor nose retracts to create a timed gap. This can suit products that need quick downward rejection, but it adds mechanical movement and needs enough time to reset without disturbing accepted flow.
Automatic ejection is not always appropriate. If the product is too large, unstable or hazardous, the safer quality response may be to stop the line, identify the failed item and require authorised manual removal.
Include the smallest, largest, lightest, heaviest and least stable variants, plus surface friction, liquid movement and fragile features.
Give the real operating range, minimum gap, speed changes, consecutive rejects and any accumulation near the inspection point.
Define where rejected product must go, who may access it and how the system should respond when removal is not confirmed.
Final selection should be based on representative products and the actual line envelope.
An air blast uses a timed jet of compressed air and is normally considered for suitable lightweight products. A pusher uses a guided mechanical face and gives positive lateral movement for products that can tolerate contact.
A correctly sized pusher or controlled diverter is often considered, but weight is only one factor. Stability, contact surface, pitch, line speed, available space and destination also matter.
There is no single high-speed answer. Air blast or retracting-belt systems may suit some applications; closely pitched or unstable products may need controlled diversion or changes to upstream product handling.
Often, yes, if all formats remain within the designed operating envelope. Change parts, adjustable guides, recipes, timing parameters and challenge tests may be needed for reliable changeover.
Unsure which method fits?
A short video, dimensions, throughput and the intended reject destination provide a useful starting point for selection.
Share the product, throughput, inspection trigger and available conveyor space. We’ll help identify a practical next step.
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