TABLE OF CONTENTS The reliability of equipment can be increased substantially by preventive, or scheduled, maintenance whereby units which are about to enter their wear-out life, or are partially worn out, or aged, or are due for a minor or a major overhaul, are replaced with new units at predetermined periods of operation of the unit or of the equipment, thus forestalling equipment failures during operation, reducing the average failure rate of the equipment, reducing the cost of failures, increasing equipment availability and productivity, and if it is production equipment decreasing the unit-cost of production.
Failures during operation may be much more expensive than preventive maintenance, since they interrupt operation at an undesirable time, and a failing part may damage many other parts adjacent to it, or may even destroy the equipment and damage other associated or adjacent equipment. Preventive maintenance results in the reduction of the total maintenance man-hours per equipment operating hour by decreasing the number of primary and secondary failures. Thus, it is often economically very advantageous to apply a policy of preventive part replacement. Furthermore if the machine's design reliability is not adequate for the intended operational life of the system in which the machine is used, its operating reliability may be increased substantially by preventive maintenance as will be shown later. Consequently, the total equipment operating and maintenance cost is decreased substantially through preventive maintenance.
Figure 9.1 illustrates the effect of preventive maintenance on the reliability bathtub curve. It may be seen that preventive...
