Another New Book Part 7

In my last post I explained that this series of posts was taken from my newest book, Theory of Constraints, Lean, and Six Sigma Improvement Methodology - Making the Case for Integration, I will be discussing how I present the basics of TOC to those readers who may not be familiar with it.

I started the last post by saying that Goldratt and Cox analogized the concept of a chain to organizations and explained that failing to identify and strengthen the organization’s weakest link, or system constraint, will not strengthen the global system.

While Goldratt and Cox used a chain analogy to define what a constraint is, I use a different approach when explaining TOC to people who aren’t familiar with what it is. As I present this different approach, remember that the Theory of Constraints is a methodology for identifying the most important limiting factor (i.e. constraint) that stands in the way of achieving your goals and then systematically improving that constraint until it is no longer the limiting factor. So, let’s look at a different way of describing TOC.

The figure below is a simple piping system used to transport water. Water enters into Section A of this piping system, then flows into Section B and continues downward through all of the pipes until it collects in the receptacle at the base of the system. In this piping system, water flows via gravity, meaning that if you wanted more water, you could not increase the pressure to get more.

In every system, there is a point that limits throughput and this piping system is no different. Think for a minute what you would have to do to achieve an increase in the flow of water through this system? Because Section E’s diameter is the smallest, does it make sense to you that if you wanted to increase the flow of water through this system, the only way you could achieve this would be to increase the diameter of this limiting point? In other words, Section E is limiting the flow of water (i.e. throughput) through this piping system and because of this, it is designated as the system constraint (aka the bottleneck). Now ask yourself what would determine how much larger Section E’s diameter must be? The answer to this basic question is that it depends upon how much more water is needed. In other words, it’s dependent upon the new demand requirement.

In the figure below, we have now opened-up Section E’s diameter and as you can see, more water is now flowing through the system. When Section E’s diameter was increased, three distinct changes took place. First, the system constraint moved from Section E to Section B because it is now the smallest diameter pipe. Second, the throughput of water increased to the limit of the new constraint (Section B), and finally, water has now begun to accumulate in front of Section B.

Ask yourself, “Would increasing the diameter of any other section have resulted in any more throughput of water?” The answer is a resounding no! Only increasing the diameter of Section E would have resulted in more water flowing through this system. The inevitable conclusion is that the system constraint controls the system throughput and focusing improvement efforts anywhere else is typically wasted effort.

In my next post we will demonstrate how this might apply to a simple manufacturing process.

Bob Sproull