Deflection
Deflection is how far a pallet bends or sags under load, measured at the point of greatest movement. Common limits are about 1.9 to 2% of the span in rack storage (roughly 0.75 in on a 44 in span), 1.5 to 2% on the floor, and 0.5 in or less for automated warehouses and AS/RS.
Also called sag, pallet sag, deflection limit
Reviewed
Typical deflection limits
| Situation | Typical limit |
|---|---|
| Rack storage | about 1.9 to 2% of the span (about 0.75 in at 44 in) |
| Floor support | 1.5 to 2% of the block or stringer span |
| Automated warehouse, AS/RS | 0.5 in or less |
How deflection is reported
PDS reports the estimated deflection after 30 days of load, because wood keeps deflecting over time (creep). A buyer can add a deflection limit, and PDS then reports the maximum load that stays within it, which can be lower than the strength-based safe working load. In the v5.2 PDS example, a 48x40 racked across its width had a strength rating of 1,630 lb but only 1,006 lb at a 0.75 in deflection limit.
Why deflection matters
Too much sag can let a pallet slip off rack beams, jam conveyors and automated systems, and crush the bottom layer of cartons. Deflection falls with stiffer members: deeper stringers, thicker deckboards, denser species and shorter spans. See pallet deflection and racking pallets.
Questions
- How much pallet deflection is acceptable?
- In racking, about 2% of the span is a common limit, roughly 0.75 in on a 44 in span. Automated systems often need 0.5 in or less.
- Can a pallet pass on strength but fail on deflection?
- Yes. A pallet can be strong enough not to break yet sag too much for racks or conveyors, so ask for both checks.
Related
- Pallet deflection: limits, creep and how to reduce sagPallet deflection is how far a loaded pallet sags. Typical limits: about 2% of span in racks, 0.5 in or less for automated systems. How creep affects it.
- CreepCreep is the slow increase in pallet deflection under a sustained load. PDS reports deflection after 30 days; plastic pallets are especially creep-sensitive.
- Rack storageRack storage means a pallet spans between two rack beams with nothing underneath. It gives the lowest rating, e.g. 1,558 lb racked vs 5,223 lb on the floor.
- Free spanFree span is the unsupported distance a pallet bridges between supports, such as rack beams. A 48 in pallet on beams typically has about a 44 in free span.
- Racking pallets: rack capacity, orientation and spanHow pallets carry load in racks: across-length vs across-width racking, beam span, bearing, deflection limits, and how to size stringers for a racked load.
- Double-faceA double-face pallet has both a top and a bottom deck. It can be non-reversible (fewer bottom boards, like a GMA 48x40) or reversible (identical decks).