Pull System
A production and inventory control methodology where resources and materials are drawn into each stage of a process based on actual downstream demand rather than forecasted requirements.
A pull system is a fundamental approach to managing flow in complex systems, particularly in manufacturing and service operations, where work is initiated in response to actual demand rather than pushing based on predictions or schedules.
The concept emerged prominently through the Toyota Production System, where it forms a core element of lean manufacturing. Pull systems represent a key implementation of demand-driven operations and contribute significantly to system optimization.
Core Principles
The fundamental mechanism of a pull system relies on:
- Signal-based activation: Work begins only when signaled by downstream demand
- Information flow that move counter to material flows
- Local autonomy in responding to signals
- Buffer management through controlled work in progress
Theoretical Foundation
Pull systems exemplify several important systems concepts:
- Feedback loops that regulate production based on actual consumption
- Self-organization properties that emerge from simple rules
- System boundaries that define where pull signals operate
- Flow optimization through constraint management
Implementation Methods
Common implementations include:
- Kanban system - Using cards or signals to trigger replenishment
- CONWIP systems
- Drum-Buffer-Rope methodology from Theory of Constraints
System Benefits
Pull systems contribute to:
- Reduced inventory levels
- Improved system resilience to variability
- Better synchronization between process steps
- Enhanced system adaptability to changing conditions
Contrasts and Relations
Pull systems stand in contrast to push system, which operate based on forecasts and schedules. The choice between pull and push often relates to underlying system characteristics including:
- System complexity
- Demand patterns
- Lead time requirements
- Process variability
Modern Applications
Beyond manufacturing, pull principles have been adapted to:
- Software development through agile methodologies
- Service operations systems
- Supply chain management
- Knowledge work organization
The concept continues to evolve with new applications in digital systems and network organization, demonstrating its fundamental value in complex adaptive systems.
Limitations and Considerations
While powerful, pull systems require careful consideration of:
- System stability requirements
- Signal quality and transmission
- Buffer design
- System responsiveness
Understanding these aspects is crucial for successful implementation and maintenance of pull systems within larger organizational contexts.