The Life Cycle Bathtub Curve For Hydraulic Components

axial piston pump failureThe 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 … continue reading »

A Word About Retermination of Hydraulic Hoses

hydraulic hoseClause 5.4.6.5.1 a) of ISO 4413:2010 “Hydraulic fluid power – General rules and safety requirements for systems and their components” states: “hose assemblies shall be constructed from hoses that have not been previously used in operation as part of another hose assembly and that fulfil all performance and marking requirements given in appropriate standards;”

This means squeezing a new end onto a hydraulic hose that has previously been in service contravenes ISO 4413:2010. In the majority of cases, the practical implications of this directive are not burdensome. After all, in most situations, the hose end outlasts the hose itself.… continue reading »

How Long Can Hydraulic Oil Really Last?

hydraulic oil drumOne of our members wrote me about a case study he read in which the life of a mineral hydraulic oil in a mobile hydraulic machine was extended from the 4,000 hours recommended by the machine’s manufacturer to 17,000 hours. The question raised was: “is this really possible?”

The first thing to keep in mind is that hydraulic oil should only be changed when either the base oil has become degraded or its additives have become depleted. Which means it should NOT be changed on an arbitrary number of hours in service. So in this respect, the 4,000 hour change … continue reading »