Developing a Preventive Maintenance System - Step 1
In a prior blog post, How to develop a preventive maintenance system , I outlined a Six Step process for determining what preventive maintenance should be done on a machine. This post describes the first step in more detail.
The First Question we ask is, “What Are the Possible Failures?”
To ask what the failures are, first we need to know what the machine is supposed to do. What is its primary function? At first glance, you might say that a pump’s primary function is to pump a liquid. In reality, its primary function is to keep a supply tank full. As the process draws liquid from the tank, the pump replaces it. If the pump can’t pump at a sufficient rate, the supply tank will go empty. That minimum rate will vary from process to process. Look beyond the obvious to the real function of the machine.
The machine may also have secondary functions. For example, our pump also has to contain the pressure in the system, it has to prevent leaks and it has to be safe for the operator. When considering failure, look at all these functions.
Once you’ve decided what the machine’s function is, ask what can happen to prevent it from meeting that function. In the case of the pump, the answer might be the impellor wearing out reducing available head, bearing failure causing low RPM, a crack in the casing or worn-out seal causing liquid to be lost reducing flow or exposing the operator to a hazardous liquid, or a number of other possible failures. In the case of the mechanical seal failing, the pump will still probably meet it's primary function, but will have failed the secondary function of keeping the fluid contained. That's still a functional failure.
At this point, you’re just brainstorming. Don’t consider whether the failure is likely or has much impact. We’ll do that in the next step. For now, just get a complete list.
Key takeaways:
To determine whether a machine has failed, you must know what it is in the system to do.
The machines function is why it was included in the system.
A machine may have both a primary function and secondary functions.
The question you must ask is “How can the machine fail to meet is function?”
Let’s try to get as complete a list of possible pump functions as possible. Put your ideas in the comment so we can all see them.
Download our paper "6 Steps to a Healthy Machine"
6 Steps to a Healthy Machine