Saturday, May 16, 2015

How I Teach the Theory of Constraints

This past week I was asked a question about how I present the basics of the Theory of Constraints to people not familiar with its teachings.  Or more specifically, how do I teach my students or improvement teams about how to understand the basic concept of constraints.  So in the next two postings I’m going to share with you a series of slides on how I present this basic concept.  For those of you who are familiar with my blog, this is a repeat posting for a couple of years ago with some slight changes.

The best way I have found to help people understand just what a constraint is and how it impacts the flow or throughput through a process is by using a simple piping system diagram with each pipe having a different diameter.  As you read this posting, remember what we are trying to demonstrate is the concept of flow and how the constraint controls it.

In this first slide I simply explain that this is a drawing of a cross section of pipes used to transport water through each section of pipe and into a collection receptacle at the bottom. I then tell them that we need more water flowing and that they have been chosen to fix this system.   I emphasize that this system is fed via gravity, so they can’t simply increase the water pressure.

In my next slide, I pose the question that if enough water isn’t flowing through this system, what must they do to make more water flow?  Someone in the group will automatically state that in order to have more water flowing through the system, we have to increase the diameter of Section E.


I ask everyone if they understand why they must increase Section E’s diameter and most will answer that they do.  For anyone who doesn’t, I simply explain that because of the constricted nature of Section E, water flow is limited at this point. Since they all now have an understanding of this basic concept, I then move to the next slide.

This slide reinforces what I just explained, but then I ask another important question about how large the new diameter should be.  In other words, what would this depend upon?  What this is supposed to demonstrate is that demand requirements play a role in determining the level of improvement needed to satisfy demand requirements.

In the next slide, I demonstrate the new diameter of Section E and how water is now flowing at a much faster rate than before the diameter change.  The important point I emphasize is that the system constraint controls the throughput of water through every section of pipe and if we don't subordinate the rest of the system to the same throughput rate as the constraint, we will automatically have a WIP build-up in front of the constraint.

I then ask the class to identify other physical changes to this system have occurred as a result of our exploitation of the constraint (i.e. increasing the diameter of Section E).

I give them time to answer this question, and most of the time the group will answer correctly.  I then post the next slide to reinforce that changes to the system.

I point out that, first and foremost, the system constraint has moved from Section E to Section B. I next explain that the new throughput of water is now governed by the rate that Section B will permit.   And finally, I point to the queue of water stacked-up in front of Section B.  I now make the point that if the amount of water is still not enough, then we must decide how to exploit the new system constraint and that the process of on-going improvement is continuous.

In my next slide I ask the question, “Would increasing the diameter of any or all other sections have resulted in any more throughput of water through this system?”  This question is intended to demonstrate that since the system constraint controls the throughput of a system, focusing improvement anywhere else in the system is usually wasted effort.  What I finish with is a before and after slide just to reinforce how things have changed by focusing on the constraint.

In my next posting, I'll present the rest of my training package moving from the abstract piping system to the real world.....a real process.

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