Pull System
How does pull differ from push in inventory control?
A pull system authorizes work from actual consumption or confirmed demand, while a push system releases work based on forecast or schedule assumptions.
What controls WIP in a pull system?
Explicit replenishment rules, supermarket limits, and downstream demand signals constrain how much material can remain in process at any time.
Why is pull often used with kanban?
Kanban is a visual or electronic demand signal that transmits consumption information upstream, so replenishment occurs only when a downstream user has actually taken material.
A pull system is a demand-driven inventory and production control method in which each upstream process, supplier, or replenishment point acts only after receiving a downstream consumption signal or confirmed order instead of a forecast-driven schedule. Production and replenishment occur in the exact quantity needed and at the time needed, authorized by kanban cards, bins, electronic signals, or similar triggers.
On the shop floor, a downstream station consumes parts from a controlled buffer or supermarket, and that consumption signal authorizes the upstream process to replenish the same part quantity into the buffer. In warehousing, replenishment is triggered by actual pick activity or minimum stock thresholds, so a location restocks only after a real usage event rather than a blanket forecast release. For raw material tracking, pull logic ties material issue to confirmed production demand, which limits work-in-process and prevents excess raw inventory from sitting idle between receiving, kitting, and line-side consumption. In a well-run pull environment, inventory level itself regulates production: when stock drops below a preset target, the upstream process replenishes only that shortage. The system works best with JIT, kanban, and explicit WIP limits; it reduces overproduction and queue buildup, but depends on disciplined signal reliability, accurate part counts, and stable process timing to avoid starvation or over-replenishment.
Lost or delayed kanban signal: If the card, bin, or electronic trigger is missed, delayed, or left unscanned, upstream replenishment never starts. Downstream stations then starve and lines stop even though parts exist elsewhere in the system.
Poorly sized supermarket buffers: Set too small for real demand variability, a supermarket empties before replenishment arrives and triggers stockouts. Set too large, it quietly becomes a push-based warehouse, rebuilding excess inventory and long lead times.
Unstable replenishment cycles: High changeover time, machine downtime, or unreliable inbound supply slows the loop faster than downstream consumption. The result is bottlenecks at receiving, kitting, or line-side staging and undermines synchronized flow.