Lean teams use pull because it caps inventory, shortens lead time and makes problems visible. Where possible they go further, to continuous flow, where items move one at a time from step to step without waiting.
Where it comes from
Pull is part of just in time in the Toyota Production System. Taiichi Ohno described how the American supermarket, where shelves are restocked only as customers take goods, inspired Toyota's kanban system.
At a glance
Push vs pull
Swipe sideways to see the whole diagram.
How to apply Pull system
- 1
Map the flow
Draw the value stream and mark where items wait. Look for steps that could be joined into continuous flow, one piece at a time.
- 2
Create flow where you can
Place connected steps next to each other and balance the work to takt time, so items move without waiting.
- 3
Pull where you cannot flow
Between steps that cannot flow, add a supermarket with set quantities, a FIFO lane with a maximum length, or a CONWIP limit on the whole loop.
- 4
Size the loops
Set the number of kanban cards or the maximum quantity from demand, replenishment time and a safety margin, and write it down.
- 5
Schedule one point
Send the customer schedule to a single pacemaker process. Everything upstream is pulled by it.
- 6
Reduce the buffers
Once the loop is stable, remove cards one at a time to expose the next problem, and fix it.
Worked example
A furniture maker used to push parts from its saw to assembly by weekly schedule, and piles of the wrong parts built up. It now keeps a small supermarket of each part beside assembly. When assembly takes a bin, the empty bin goes back to the saw as the signal to cut more. Work in progress falls and the saw cuts what assembly actually uses.
Common mistakes
- Adding kanban cards without sizing them, so the loop holds as much stock as the old push system.
- Scheduling several processes instead of one pacemaker, so push and pull fight each other.
- Starting pull on an unstable process, where breakdowns empty the supermarket and stop the line.
When Pull system is not the right tool
Pull needs fairly steady demand and reliable processes. For one-off custom work, a sequenced pull with FIFO lanes or a CONWIP limit often works better than supermarkets.
Supermarkets, FIFO lanes and CONWIP
A supermarket holds a small, fixed stock of each part. When the next step takes one, the empty space or card tells the supplying step to make another.
A FIFO lane holds a maximum number of items in order. When it is full, the step feeding it stops. CONWIP caps total work in progress across a loop, releasing new work only when finished work leaves.