The original life cycle bathtub curve was based on the cycle of human life. And at some point last century it was adapted by reliability engineers working in the electronics manufacturing industry to graphically represent the failure rate of their products. As you can see from its depiction below, the Observed Failure Rate-the top, bathtub curve, is the product of the three curves below it: Infant Mortality Failures, Wear Out Failures and a near constant rate of Random Failures.

One glance and it’s obvious the bathtub curve is just as pertinent to the life cycle of hydraulic components as it is to humans or electronic devices. And in a hydraulics maintenance context, it’s useful for framing our expectations and objectives. For example, we should accept that there will be some level of random failures resulting from manufacturing defects and circuit design faults. There’s not much we can do about manufacturing defects in a maintenance environment. But where analysis of a random failure indicates a circuit design fault, this can and should be rectified to prevent recurring failures.