Unlike a push system, where work is pushed onto teams regardless of their capacity, pull systems prevent team overburden and increase workflows efficiency. Teams pull work as they finish what they started while keeping their focus on the highest priorities. Kanban pull systems significantly improve productivity and decrease delivery times.
How Does the Kanban Pull System Work?
To implement and maintain a pull system with the Kanban Method, you need to follow four main steps: visualize your workflow, establish a pull system, limit work in progress, and apply pull signals.
Visualize your Workflow
To visualize your workflow, you need to map your value stream. This starts with defining each step of the process and listing it on a Kanban board. Each column on the board corresponds to a process state, and each card represents a task. Each task should clearly display essential information, such as the type of task, its class of service, and the people assigned to that task. Tasks flow through the process as cards move from left to right through the board. This gives your teams complete visibility into their workflows and improves collaboration within the team.
Establish a Pull System
Instead of pushing tasks into the process, teams pull work only when there is a demand for it, and they have the capacity to handle that demand. Every process state has an ‘In progress (IP)’ and ‘Done’ column. For example, if a task passes code review, it moves to the ‘Code Review (Done)’ column. ‘Done’ columns are often referred to as queue states. These are passive since no one works on tasks in the queue states. In our example, ‘Code review (Done)’ is the queue from which testing teams pull tasks ready for testing once they have the capacity to handle new work. By pulling work, teams eliminate multitasking and stay focussed on the highest priorities. This leads to increased throughput and reduced cycle times which, in turn, means happier customers and greater profitability.
Limit Work in Progress
Establishing a pull system by itself isn’t enough to support an efficient workflow. Your process can still get stuck if there are too many tasks in progress. You need to control the amount of work that goes in and out of the system by applying limits to each process state. Work in progress (WIP) limits help teams focus on getting things done.
Apply Pull Signals
A key component of a pull system is the use of pull signals to indicate that new tasks are ready to be handled. In a Kanban pull system, a pull signal is triggered when the number of cards in a column drops beneath the specified limit. This is a signal to the previous column that a new task can move further. Once the work in progress limit is reached, no more tasks may be pulled until an outstanding one has been completed first. This prevents team burnout by ensuring that they only have as much work as they’re able to manage. It also helps prevent tasks from being neglected.
Eliminating Bottlenecks to Maximise Process Efficiency
The Kanban pull system gives you the ability to track and reduce waiting time. By observing your queue states, you can assess how much time work is sitting idle. Keeping track of waiting time reveals your process bottlenecks right away. Waiting time is a Muda, one of the 3 Lean Manufacturing wastes that cause bottlenecks in your system. If there’s too much work in a queue state, it becomes immediately visible on the Cumulative Flow Diagram (CFD).
On the CFD, every band corresponds to a step in your workflow. The bands that represent queue states should either disappear or remain very small. This would mean that there are no tasks in the queue or only a few sitting there. However, if the queue state bands are getting wider, your team is having difficulty handling all the work that arrives. If there are too many tasks staying in these states, then the chances of delay increase significantly.
If your team has too much work, they will be forced to choose which tasks to pick up. If tasks have the same class of service, team members will likely pull the fastest and easiest ones first. Unfortunately, this approach only generates flow debt, causing older and more complicated tasks to mount up further without anyone taking care of them. To alleviate this problem, you should introduce pull policies, specifying the order in which tasks should be pulled in each state. This approach increased our performance by 250%.
Keeping Track of WIP to Avoid Delays
It’s important to observe how many tasks there are in each queue state and how much time each task spends in that state. That’s where the Aging Chart comes in. It uses the same visual format as your Kanban board, with each column representing a process state. Dots indicate work items in progress. The left vertical axis displays the number of days that tasks have spent in your workflow. On the right, percentile lines show the percentage of tasks being completed within certain cycle time. Keep a look out for tasks above the 50th percentile, since they have been in progress for longer than half of the tasks completed so far. The higher the dot, the more likely the chance of a delay.
Queue states are passive states, and they don’t need dedicated WIP limits. Taking that in mind, team members with free capacity should avoid falling into the trap of pulling more work, otherwise, your process will get stuck. Based on Little’s Law, if your WIP increases, it will take more time on average to deliver your work. To prevent this from happening, make it explicit that the number of tasks in a queue state counts as work in progress for the current step. For example, if you have a Development column with a WIP limit of 5 items, and a queue state Development (Done), then the tasks in both Development and Development (Done) columns have a limit of 5 items in total.
Implementing a pull system optimizes process efficiency, increases team performance, and prevents overburden. It enables you to identify how much time it really takes for your team to create value and how much time they need to deliver it. As the team pulls items and reduces waiting times in your process, delivery speed will increase, and that means more engaged employees and happier customers. Empowered by a Kanban pull system, your team will also be better equipped to manage change and scale with demand. Those are crucial benefits when it comes to keeping up to speed with the demands of today’s fast-evolving market.
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